Milk from different species on physicochemical and microstructural yoghurt properties

Influência do leite de diferentes espécies nas propriedades físico-químicas e micro estruturais do iogurte

Felipe Santana Vianna Anna Carolina Vilhena da Cruz Silva Canto Bruno Costa-Lima Ana Paula Salim Celso Fasura Balthazar Marion Pereira Costa Pedro Panzenhagen Rachel Rachid Robson Maia Franco Carlos Adam Conte-Junior Adriana Cristina de Oliveira Silva About the authors

ABSTRACT:

The aim of the present research was to evaluate differences in chemical properties and physical structure of yoghurt produced with milk from different species (sheep, cow, and goat). For each trial, whole raw sheep (S), cow (C), and goat (G) milk were used to manufacture 4L of yoghurts (Y) from each species (SY, CY, and GY, respectively). The SY demonstrated the greatest (P<0.05) values of total solids, protein, and lipid contents, reflecting on greater (P<0.05) firmness, apparent viscosity and water-holding capacity, and lower (P<0.05) syneresis index than CY and GY. Consequently, SY exhibited a more compact microstructure and homogeneous matrix with fewer pores. Furthermore, CY and GY microstructure contained a greater number of pores, which exhibited greater size heterogeneity than SY. Therefore, based on the evaluated physicochemical and microstructural properties of yoghurt, SY demonstrated the most desirable parameter values for dairy industry representing an alternative substitution for cow’s milk yogurt.

Key words:
fermented products; texture; microstructure; sheep milk; goat milk

RESUMO:

O objetivo da presente pesquisa foi avaliar as diferenças nas propriedades químicas e na estrutura física do iogurte produzido com leite de diferentes espécies (ovinos, bovinos e caprinos). Para cada experimento, leite de ovelha cru (S), vaca (C) e cabra (G), foram usados para fabricar 4L de iogurtes (Y) de cada espécie (SY, CY e GY, respectivamente). O SY demonstrou os maiores (P<0,05) valores de sólidos totais, proteína e conteúdo lipídico, refletindo em maior (P<0,05) firmeza, viscosidade aparente e capacidade de retenção de água e menor (P<0,05) índice de sinérese do que CY e GY. Consequentemente, o SY exibiu uma microestrutura mais compacta e uma matriz homogênea com menos poros. Além disso, a microestrutura CY e GY continha um maior número de poros, que exibiam maior heterogeneidade de tamanho do que o SY. Portanto, com base nas propriedades físico-químicas e micro estruturais avaliadas do iogurte, o SY demonstrou os valores de parâmetros mais desejáveis para a indústria de laticínios, representando uma alternativa de produto adequada aos iogurtes à base de leite de vaca.

Palavras-chave:
leite fermentado; textura; microestrutura; leite de ovelha; leite de cabra

INTRODUCTION:

Yoghurt represents a great source of health-promoting substances due to high levels of viable lactic acid bacteria content, which compete with several opportunistic microorganisms and provide desirable metabolites (MCKINLEY, 2005MCKINLEY, M. C. The nutrition and health benefits of yoghurt. International Journal of Dairy Technology, v.58, n.1, p.1-12. 2005. Available from: <Available from: http://onlinelibrary.wiley.com/doi/10.1111/j.1471-0307.2005.00180.x/abstract >. Accessed: Feb. 22, 2018. doi: 10.1111/j.1471-0307.2005.00180.x.
http://onlinelibrary.wiley.com/doi/10.11...
; IRKIN & VAPUR EREN, 2008IRKIN, R.; U. VAPUR EREN. A research about viable Lactobacillus bulgaricus and Streptococcus thermophilus numbers in the market yoghurts. World Journal of Dairy & Food Sciences, v.3, n.1, p.25-28. 2008. Available from: <Available from: https://www.semanticscholar.org/paper/A-Research-about-Viable-Lactobacillus-bulgaricus-in-Irkin-Eren/737df679fcd6708cbdb4393054fb222530debb5c2018/02/22 >. Accessed: Feb. 22, 2018.
https://www.semanticscholar.org/paper/A-...
; ERKAYA & ŞENGÜL, 2012ERKAYA, T.; M. ŞENGÜL. A comparative study on some quality properties and mineral contents of yoghurts produced from different type of milks. Kafkas Universitesi Veteriner Fakultesi Dergisi, v.18, n.2. 2012. Available from: <Available from: http://vetdergikafkas.org/uploads/pdf/pdf_KVFD_1100.pdf >. Accessed: Feb. 22, 2018. doi: 10.9775/kvfd.2011.5498.
http://vetdergikafkas.org/uploads/pdf/pd...
; SETTACHAIMONGKON et al., 2014SETTACHAIMONGKON, S., et al. Influence of different proteolytic strains of Streptococcus thermophilus in co-culture with Lactobacillus delbrueckii subsp. bulgaricus on the metabolite profile of set-yoghurt. International Journal of Food Microbiology, v.177, p.29-36. 2014. Available from: <Available from: http://www.ncbi.nlm.nih.gov/pubmed/24598513 >. Accessed: Feb. 26, 2018. doi: 10.1016/j.ijfoodmicro.2014.02.008.
http://www.ncbi.nlm.nih.gov/pubmed/24598...
; COSTA et al., 2015aCOSTA, M. P., et al. Determination of biogenic amines by high-performance liquid chromatography (HPLC-DAD) in probiotic cow’s and goat’s fermented milks and acceptance. Food Science & Nutrition, v.3, n.3, p.172-178. 2015a. Available from: <Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4431784/ >. Accessed: 2018/02/22/13:13:09. doi: 10.1002/fsn3.200.
https://www.ncbi.nlm.nih.gov/pmc/article...
; COSTA et al., 2017COSTA, M. P., et al. Consumer perception, health information, and instrumental parameters of cupuassu (Theobroma grandiflorum) goat milk yogurts. Journal of Dairy Science, v.100, n.1, p.157-168. 2017. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0022030216307433 >. Accessed: Feb. 22, 2018. doi: 10.3168/jds.2016-11315.
http://www.sciencedirect.com/science/art...
) that contribute to consumer health and the development of yoghurt aroma and flavour (CHENG, 2010CHENG, H. Volatile flavor compounds in yogurt: a review. Critical Reviews in Food Science and Nutrition, v.50, n.10, p.938-950. 2010. Available from: <Available from: http://www.ncbi.nlm.nih.gov/pubmed/21108074 >. Accessed: Feb. 22, 2018. doi: 10.1080/10408390903044081.
http://www.ncbi.nlm.nih.gov/pubmed/21108...
). Yoghurt can be produced utilizing milk from different species (TAMIME & ROBINSON, 2007TAMIME, A. Y.; R. K. ROBINSON. Tamime and Robinson’s Yoghurt, Third Edition: Science and Technology. Cambridge: Woodhead Publishing. 2007. 808 p.). Furthermore, yoghurt characteristics such as convenience, price and flavour are important attributes determinant to consumer final product acceptability (POHJANHEIMO & SANDELL, 2009POHJANHEIMO, T.; M. SANDELL. Explaining the liking for drinking yoghurt: the role of sensory quality, food choice motives, health concern and product information. International Dairy Journal, v.19, n.8, p.459-466. 2009. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0958694609000545 >. Accessed: Feb. 26, 2018. doi: 10.1016/j.idairyj.2009.03.004.
http://www.sciencedirect.com/science/art...
; COSTA et al., 2017COSTA, M. P., et al. Consumer perception, health information, and instrumental parameters of cupuassu (Theobroma grandiflorum) goat milk yogurts. Journal of Dairy Science, v.100, n.1, p.157-168. 2017. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0022030216307433 >. Accessed: Feb. 22, 2018. doi: 10.3168/jds.2016-11315.
http://www.sciencedirect.com/science/art...
).

Previous studies in dairy science commonly utilized cow milk potentially due to their large volume and economic importance (AL-SHERAJI et al., 2012AL-SHERAJI, S. H., et al. Hypocholesterolaemic effect of yoghurt containing Bifidobacterium pseudocatenulatum G4 or Bifidobacterium longum BB536. Food Chemistry, v.135, n.2, p.356-361. 2012. Available from: <Available from: http://www.ncbi.nlm. nih.gov/pubmed/22868099 >. Accessed: Feb. 22, 2018. doi: 10.1016/j.foodchem.2012.04.120.
http://www.ncbi.nlm. nih.gov/pubmed/2286...
; MAYER et al., 2012MAYER, H. K., et al. Quantification of cow’s milk percentage in dairy products - a myth? Analytical and Bioanalytical Chemistry, v.403, n.10, p.3031-3040. 2012. Available from: <Available from: http://www.ncbi.nlm.nih.gov/pubmed/22349339 >. Accessed: Feb. 22, 2018. doi: 10.1007/s00216-012-5805-1.
http://www.ncbi.nlm.nih.gov/pubmed/22349...
; LEE et al., 2013LEE, H., et al. Quantitative analysis of gangliosides in bovine milk and colostrum-based dairy products by ultrahigh performance liquid chromatography-tandem mass spectrometry. Journal of Agricultural and Food Chemistry, v.61, n.40, p.9689-9696. 2013. Available from: <Available from: http://www.ncbi.nlm.nih.gov/pubmed/24024650 >. Accessed: Feb. 22, 2018. doi: 10.1021/jf402255g.
http://www.ncbi.nlm.nih.gov/pubmed/24024...
; WEN et al., 2014WEN, Y., et al. Quality indices of the set-yoghurt prepared from bovine milk treated with horseradish peroxidase. Journal of Food Science and Technology, v.51, n.8, p.1525-1532. 2014. Available from: <Available from: http://www.ncbi.nlm.nih.gov/pubmed/25114343 >. Accessed: Feb. 26, 2018. doi: 10.1007/s13197-012-0680-5.
http://www.ncbi.nlm.nih.gov/pubmed/25114...
; ZHANG et al., 2014ZHANG, J., et al. Determination of bovine lactoferrin in dairy products by ultra-high performance liquid chromatography-tandem mass spectrometry based on tryptic signature peptides employing an isotope-labeled winged peptide as internal standard. Analytica Chimica Acta, v.829, p.33-39. 2014. Available from: <Available from: http://www.ncbi.nlm.nih.gov/pubmed/24856400 >. Accessed: Feb. 26, 2018. doi: 10.1016/j.aca.2014.04.025.
http://www.ncbi.nlm.nih.gov/pubmed/24856...
). Nonetheless, in many countries specific climatic and geographical features favor dairy goat and sheep farming, making such activity essential for the national and regional economy (PANDYA & GHODKE, 2007PANDYA, A. J.; K. M. GHODKE. Goat and sheep milk products other than cheeses and yoghurt. Small Ruminant Research, v.68, n.1, p.193-206. 2007. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0921448806002483 >. Accessed: Feb. 22, 2018. doi: 10.1016/j.smallrumres.2006.09.007.
http://www.sciencedirect.com/science/art...
; PARK et al., 2007PARK, Y. W., et al. Physico-chemical characteristics of goat and sheep milk. Small Ruminant Research, v.68, n.1, p.88-113. 2007. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0921448806002549 >. Accessed: Feb. 26, 2018. doi: 10.1016/j.smallrumres.2006.09.013.
http://www.sciencedirect.com/science/art...
). In addition, goat milk products have essential characteristics for human nutrition as higher digestibility (small fat globules) and less allergenicity (low αs1-casein content) (UYSAL-PALA et al., 2006UYSAL-PALA, C., et al. Sensory properties of drinkable yogurt made from milk of different goat breeds. Journal of Sensory Studies, v.21, n.5, p.520-533. 2006. Available from: <Available from: http://onlinelibrary.wiley.com/doi/10.1111/j.1745-459X.2006.00077.x/abstract >. Accessed: Feb. 26, 2018. doi: 10.1111/j.1745-459X.2006.00077.x.
http://onlinelibrary.wiley.com/doi/10.11...
). Moreover, sheep milk products have high nutritive and organoleptic traits due to greater contents of proteins, linolenic acid, essential amino acids, vitamins, and minerals when compared to cow milk products (KAMINARIDES et al., 2007KAMINARIDES, S., et al. Comparison of the characteristics of set type yoghurt made from ovine milk of different fat content. International Journal of Food Science & Technology, v.42, n.9, p.1019-1028. 2007. Available from: <Available from: http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2621.2006.01320.x/abstract >. Accessed: Feb. 22, 2018. doi: 10.1111/j.1365-2621.2006.01320.x.
http://onlinelibrary.wiley.com/doi/10.11...
; PARK et al., 2007PARK, Y. W. Rheological characteristics of goat and sheep milk. Small Ruminant Research, v.68, n.1, p.73-87. 2007. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0921448806002562 >. Accessed: Feb. 26, 2018. doi: 10.1016/j.smallrumres.2006.09.015.
http://www.sciencedirect.com/science/art...
). Furthermore, previous studies have demonstrated that the aforementioned milks can be used for the production of fermented dairy products (KATSIARI et al., 2002KATSIARI, M. C., et al. Manufacture of yoghurt from stored frozen sheep’s milk. Food Chemistry, v.77, n.4, p.413-420. 2002. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0308814601003673 >. Accessed: Feb. 22, 2018. doi: 10.1016/S0308-8146(01)00367-3.
http://www.sciencedirect.com/science/art...
; PAPADIMITRIOU et al., 2007PAPADIMITRIOU, C. G., et al. Identification of peptides in traditional and probiotic sheep milk yoghurt with angiotensin I-converting enzyme (ACE)-inhibitory activity. Food Chemistry, v.105, n.2, p.647-656. 2007. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0308814607003810 >. Accessed: Feb. 22, 2018. doi: 10.1016/j.foodchem.2007.04.028.
http://www.sciencedirect.com/science/art...
; SANAL et al., 2011SANAL, H., et al. Profiles of non-essential trace elements in ewe and goat milk and their yoghurt, Torba yoghurt and whey. Food Additives & Contaminants. Part B, Surveillance, v.4, n.4, p.275-281. 2011. Available from: <Available from: http://www.ncbi.nlm.nih.gov/pubmed/24786251 >. Accessed: Feb. 26, 2018. doi: 10.1080/19393210.2011.617520.
http://www.ncbi.nlm.nih.gov/pubmed/24786...
; ŞENEL et al., 2011ŞENEL, E., et al. Changes in some properties of strained (Süzme) goat’s yoghurt during storage. Small Ruminant Research, v.99, n.2, p.171-177. 2011. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0921448811001179 >. Accessed: Feb. 26, 2018. doi: 10.1016/j.smallrumres.2011.03.042.
http://www.sciencedirect.com/science/art...
; DE RENOBALES et al., 2012DE RENOBALES, M., et al. Part-time grazing improves sheep milk production and its nutritional characteristics. Food Chemistry, v.130, n.1, p.90-96. 2012. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0308814611009496 >. Accessed: Feb. 22, 2018. doi: 10.1016/j.foodchem.2011.07.002.
http://www.sciencedirect.com/science/art...
; DOMAGAŁA et al., 2013DOMAGAŁA, J., et al. The effect of transglutaminase concentration on the texture, syneresis and microstructure of set-type goat’s milk yoghurt during the storage period. Small Ruminant Research, v.112, n.1, p.154-161. 2013. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0921448812005202 >. Accessed: Feb. 22, 2018. doi: 10.1016/j.smallrumres.2012.12.003.
http://www.sciencedirect.com/science/art...
; SILVA et al., 2017SILVA, V. L. M., et al. Stability of polyphenols from blueberry (Vaccinium corymbosum L.) in fermented dairy beverage. Journal of Food Processing and Preservation, v.41, n.6, p.n/a-n/a. 2017. Available from: <Available from: http://onlinelibrary.wiley.com/doi/10.1111/jfpp.13305/abstract >. Accessed: Feb. 26, 2018. doi: 10.1111/jfpp.13305.
http://onlinelibrary.wiley.com/doi/10.11...
; VIEIRA et al., 2017VIEIRA, C. P., et al. Lactococcus lactis ssp. cremoris MRS47, a potential probiotic strain isolated from kefir grains, increases cis-9, trans-11-CLA and PUFA contents in fermented milk. Journal of Functional Foods, v.31, p.172-178. 2017. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S1756464617300580 >. Accessed: Feb. 26, 2018. doi: 10.1016/j.jff.2017.01.047.
http://www.sciencedirect.com/science/art...
).

Yoghurt microstructure is composed by a protein network of casein micelle aggregates entrapping fat globules and serum which directly influences this type of fermented product texture (HERRERO & REQUENA, 2006HERRERO, A. M.; T. REQUENA. The effect of supplementing goats milk with whey protein concentrate on textural properties of set-type yoghurt. International Journal of Food Science & Technology, v.41, n.1, p.87-92. 2006. Available from: <Available from: http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2621.2005.01045.x/abstract >. Accessed: Feb. 22, 2018. doi: 10.1111/j.1365-2621.2005.01045.x.
http://onlinelibrary.wiley.com/doi/10.11...
; NGUYEN et al., 2015NGUYEN, H. T. H., et al. Homogenisation improves the microstructure, syneresis and rheological properties of buffalo yoghurt. International Dairy Journal, v.46, p.78-87. 2015. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0958694614001654 >. Accessed: Feb. 22, 2018. doi: 10.1016/j.idairyj.2014.08.003.
http://www.sciencedirect.com/science/art...
). This yoghurt microstructure and textural properties are directly associated with desirable functional and sensory parameters (LEE & LUCEY, 2003LEE, W.-J.; J. A. LUCEY. rheological properties, whey separation, and microstructure in set-style yogurt: effects of heating temperature and incubation temperature. Journal of Texture Studies, v.34, n.5-6, p.515-536. 2003. Available from: <Available from: http://onlinelibrary.wiley.com/doi/10.1111/j.1745-4603.2003.tb01079.x/abstract >. Accessed: Feb. 22, 2018. doi: 10.1111/j.1745-4603.2003.tb01079.x.
http://onlinelibrary.wiley.com/doi/10.11...
; RAO & SILVA, 2007RAO, M. A.; J. A. L. D. SILVA. Role of rheological behavior in sensory assessment of foods and swallowing. in: (Ed.). Rheology of Fluid and Semisolid Foods: Springer, Boston, MA, 2007. Role of rheological behavior in Sensory Assessment of Foods and Swallowing, p.403-426. (Food Engineering Series).). In addition, previous studies have documented relation between yoghurt textural properties and microstructure (DOMAGAŁA, 2009DOMAGAŁA, J. Instrumental texture, syneresis and microstructure of yoghurts prepared from goat, cow and sheep milk. International Journal of Food Properties, v.12, n.3, p.605-615. 2009. Available from: <Available from: https://doi.org/10.1080/10942910801992934 >. Accessed: Feb. 22, 2018. doi: 10.1080/10942910801992934.
https://doi.org/10.1080/1094291080199293...
; WANG et al., 2012WANG, W., et al. Consistency, microstructure and probiotic survivability of goats’ milk yoghurt using polymerized whey protein as a co-thickening agent. International Dairy Journal, v.24, n.2, p.113-119. 2012. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0958694611002214 >. Accessed: Feb. 26, 2018. doi: 10.1016/j.idairyj.2011.09.007.
http://www.sciencedirect.com/science/art...
; NGUYEN et al., 2014aNGUYEN, H. T. H., et al. The effect of fermentation temperature on the microstructure, physicochemical and rheological properties of probiotic buffalo yoghurt. Food and Bioprocess Technology, v.7, n.9, p.2538-2548. 2014a. Available from: <Available from: https://link.springer.com/article/10.1007/s11947-014-1278-x >. Accessed: Feb. 22, 2018. doi: 10.1007/s11947-014-1278-x.
https://link.springer.com/article/10.100...
; NGUYEN et al., 2014bNGUYEN, H. T. H., et al. Microstructure and physicochemical properties of probiotic buffalo yoghurt during fermentation and storage: a comparison with bovine yoghurt. Food and Bioprocess Technology. 2014b. Available from: <Available from: http://agris.fao.org/agris-search/search.do?recordID=US201400086722 >. Accessed: Feb. 22, 2018. doi: 10.1007/s11947-013-1082-z.
http://agris.fao.org/agris-search/search...
; YANG et al., 2014YANG, T., et al. Effect of exopolysaccharides from lactic acid bacteria on the texture and microstructure of buffalo yoghurt. International Dairy Journal, v.34, n.2, p.252-256. 2014. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0958694613002239 >. Accessed: Feb. 26, 2018. doi: 10.1016/j.idairyj.2013.08.007.
http://www.sciencedirect.com/science/art...
; NGUYEN et al., 2015PANDYA, A. J.; K. M. GHODKE. Goat and sheep milk products other than cheeses and yoghurt. Small Ruminant Research, v.68, n.1, p.193-206. 2007. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0921448806002483 >. Accessed: Feb. 22, 2018. doi: 10.1016/j.smallrumres.2006.09.007.
http://www.sciencedirect.com/science/art...
). Electron scanning microscopy is a reliable tool to visualize yoghurt structure facilitating the characterization of protein chains, microorganisms, fat globules, carbohydrates, and clusters (NAKTHONG, 2012NAKTHONG, S. Effect of flour on the microstructure of goat milk yoghurt. Journal of Animal and Veterinary Advances, v.11, n.23, p.4413-4416. 2012. Available from: <Available from: http://www.medwelljournals.com/abstract/?doi=javaa.2012.4413.4416 >. Accessed: Feb. 22, 2018. doi: 10.3923/javaa.2012.4413.4416
http://www.medwelljournals.com/abstract/...
). Moreover, differences in physicochemical characteristics among milk from different species (PARK et al., 2007PARK, Y. W., et al. Physico-chemical characteristics of goat and sheep milk. Small Ruminant Research, v.68, n.1, p.88-113. 2007. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0921448806002549 >. Accessed: Feb. 26, 2018. doi: 10.1016/j.smallrumres.2006.09.013.
http://www.sciencedirect.com/science/art...
) directly influence yoghurt textural properties (SHAKEEL HANIF et al., 2012SHAKEEL HANIF, M., et al. Effect of storage on rheological and sensory characteristics of cow and buffalo milk yogurt. The Pakistan Journal of Food Science, v.22, n.2, p.61-70. 2012. Available from: <Available from: https://www.researchgate.net/publication/311902254_Effect_of_storage_on_rheological_and_sensory_characteristics_of_cow_and_buffalo_milk_yogurt >. Accessed: Feb. 26, 2018.
https://www.researchgate.net/publication...
). These properties represent important sensory parameters for product acceptability (COSTA et al., 2016aCOSTA, M. P., et al. Effect of different fat replacers on the physicochemical and instrumental analysis of low-fat cupuassu goat milk yogurts. The Journal of Dairy Research, v.83, n.4, p.493-496. 2016a. Available from: <Available from: http://www.ncbi.nlm.nih.gov/pubmed/27845025 >. Accessed: Feb. 22, 2018. doi: 10.1017/S0022029916000674.
http://www.ncbi.nlm.nih.gov/pubmed/27845...
). Thus, typical defects in yoghurts as low viscosity, reduced firmness (TAMIME & ROBINSON, 2007TAMIME, A. Y.; R. K. ROBINSON. Tamime and Robinson’s Yoghurt, Third Edition: Science and Technology. Cambridge: Woodhead Publishing. 2007. 808 p.), and high level of syneresis can lead to consumer product rejection (AMATAYAKUL et al., 2006AMATAYAKUL, T., et al. Physical characteristics of set yoghurt made with altered casein to whey protein ratios and EPS-producing starter cultures at 9 and 14% total solids. Food Hydrocolloids, v.20, n.2, p.314-324. 2006. Available from: <Available from: http://www.sciencedirect.com /science/article/pii/S0268005X05001050 >. Accessed: Feb. 22, 2018. doi: 10.1016/j.foodhyd.2005.02.015.
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). In this context, the present study aimed to compare chemical, textural and microstructural properties of yoghurts produced utilizing sheep, cow and goat milk.

MATERIALS AND METHODS:

Yoghurt processing

Freeze dried direct vat set starter culture YF-L903 containing 9.37 log CFU/g of Streptococcus thermophilus and 12.13 log CFU/g Lactobacillus delbrueckii subsp. bulgaricus (Yo-Flex®, Chr Hansen, Valinhos, São Paulo, Brazil) were prepared according to BALTHAZAR et al. (2015BALTHAZAR, C. F., et al. Sensory evaluation of ovine milk yoghurt with inulin addition. International Journal of Dairy Technology, v.68, n.2, p.281-290. 2015. Available from: <Available from: http://onlinelibrary.wiley.com/doi/10.1111/1471-0307.12189/abstract >. Accessed: Feb. 22, 2018. doi: 10.1111/1471-0307.12189.
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). For each trial, a total of 12 L whole raw sheep (SM), cow (CM) and goat (GM) milks were obtained from farms located in Vassouras (Rio de Janeiro, Brazil), Miracema (Rio de Janeiro, Brazil) and São Gonçalo (Rio de Janeiro, Brazil), respectively, to produce 4 L of yoghurts from each species. The (SM), (CM) and (GM) were collected from animals’ flock belonging to the breed Lacaune, Brazilian Girolando and Saanen, respectively. At pilot plant of Dairy Laboratory of Universidade Federal Fluminense, each type of milk was pasteurized at 85 ºC for 30 min in a stainless-steel double jacket container (GCA Corporation, Greensboro, North Carolina, United States) and cooled to 40 ºC. Aliquots from starter culture were inoculated at a concentration of 1% (v/v) into whole pasteurized milk. After homogenization aliquots of milk (200 mL) from each species were transferred to flasks and fermented at 43 ºC until the pH reached approximately 4.5 according to AOAC 981.12 for pH measurement of Acidified Foods (AOAC, 2012AOAC. Official methods of analysis. Washington: association of official analytical chemists. 2012), followed by rapid cooling. Yoghurts from different species were stored during 28 days under refrigeration (4 ºC), and bacteriological, chemical, textural, and microstructural parameters were evaluated. When all the analysis were being evaluated, we certified that temperature was kept under 7 ºC to avoid any detriment in the results. Two trials of yoghurt processing were performed for each species.

Bacteriological analysis

Streptococcus thermophilus count was performed utilizing M17 agar (Difco Company, Kansas, United States) and incubation at 37 ºC for 48 h under aerobic condition whereas, Lactobacillus delbrueckii ssp. bulgaricus was counted on MRS agar (Difco Company, Kansas, United States) at 37 ºC for 72 h under anaerobic condition utilizing anaerobic jar (Probac do Brasil, Rio de Janeiro, Brazil), both according to Codex Alimentarius standard for fermented milk in order to characterize the fermented product as yoghurt (Codex Alimentarius 2010). The bacteriological counts were analyzed in triplicate after yoghurt production on 1st and 28th days of storage (4 °C) for each trial.

Proximate composition

Proximate composition was determined on the final product (day 1 of storage) in triplicate according to AOAC (2012) procedures for each trial. Yoghurt total solids content was determined by gravimetric method using a drying oven until constant weight (AOAC 925.23), protein content was estimated by the Kjeldahl technique (AOAC 991.22), lipid content was obtained by the Gerber method (AOAC 2000.18), and ash content was determined after incineration at 550 °C in muffle furnace (AOAC 945.46).

Carbohydrates and organic acids

Carbohydrates (lactose, galactose, and glucose) and organic acids (lactic, citric, and formic acids) were determined by high-performance liquid chromatography (HPLC). Extraction of these molecules was carried out as described by González de Llano et al. (1996) with slight modifications (COSTA et al., 2016bCOSTA, M. P. D., et al. Simultaneous analysis of carbohydrates and organic acids by HPLC-DAD-RI for monitoring goat’s milk yogurts fermentation. Talanta, v.152, p.162-170. 2016b. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0039914016300601 >. Accessed: Feb. 22, 2018. doi: 10.1016/j.talanta.2016.01.061.
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). Briefly, 5 mL of H2SO4 (45 mmol/L) was added to 1 g of yoghurt samples and homogenized for 1 min in the vortex. Then, the solution was stirred for 1 h in a shaker table and centrifuged at 5,000 × g for 30 min at 4º C. The decanted was collected and filtered through Whatman no.1 filter paper. Filtered samples were injected (20 μL) in triplicate into HPLC system (Shimadzu® Kyoto, Japan) integrated with CBM-20A, connected to SPD-M20A diode array and refractive index RID-10A detectors. An Aminex HPX-87H column (300 x 7.8 mm) (Bio-Rad, Hercules, CA, USA), maintained at 60 ºC by oven column, was used. Carbohydrates identification was performed by a refractive index detector, whereas organic acids with a diode array detector at 210 nm. The chromatographic separation was achieved using 3 mM sulfuric acid solution at the isocratic condition and a flow rate of 0.5 mL.min-1. Standard solutions of carbohydrates and organic acids (Sigma, St. Louis, MO) were utilized in order to plot external standard curves and carry out the quantitative analysis of the aforementioned molecules. All carbohydrates and organic acids were well separated in a 30-min total run time with good peak resolution, sharpness and symmetry. These analyses were evaluated in triplicate during the storage period (4 °C) on days 1, 7, 14, 21 and 28 for each trial.

Analysis of pH and titratable acidity

The pH values were measured according to NGUYEN et al. (2014aNGUYEN, H. T. H., et al. The effect of fermentation temperature on the microstructure, physicochemical and rheological properties of probiotic buffalo yoghurt. Food and Bioprocess Technology, v.7, n.9, p.2538-2548. 2014a. Available from: <Available from: https://link.springer.com/article/10.1007/s11947-014-1278-x >. Accessed: Feb. 22, 2018. doi: 10.1007/s11947-014-1278-x.
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) with a digital pH meter (Digimed® Model DM-32, São Paulo, Brazil). Yoghurts titratable acidity (TA) were determined by a volume of 0.5 mL of phenolphthalein (5% w/v), as an indicator added to 10 g of yoghurt following titration with 0.1 M sodium hydroxide (NaOH) solution to an end point of stable faint pink color for 1 min; TA was expressed as lactic acid percentage (TAMJIDI et al., 2012TAMJIDI, F., et al. Physicochemical and sensory properties of yogurt enriched with microencapsulated fish oil. Food Science and Technology International = Ciencia Y Tecnologia De Los Alimentos Internacional, v.18, n.4, p.381-390. 2012. Available from: <Available from: http://www.ncbi.nlm.nih.gov/pubmed/22859650 >. Accessed: Feb. 26, 2018. doi: 10.1177/1082013211428212.
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). These analyses were performed in triplicate during fermentation and storage period (4 °C) on days 1, 7, 14, 21 and 28 for each trial.

Firmness

Firmness was determined at 5 °C by the Instrumental Texture Analyzer (TA-XT plus®, Stable Micro System Ltd., Godalming, Waverley District, United Kingdom) equipped with a 5 kg load cell according to PASEEPHOL et al. (2008PASEEPHOL, T., et al. Rheology and texture of set yogurt as affected by inulin addition. Journal of Texture Studies, v.39, n.6, p.617-634. 2008. Available from: <Available from: http://onlinelibrary.wiley.com/doi/10.1111/j.1745-4603.2008.00161.x/abstract >. Accessed: Feb. 26, 2018. doi: 10.1111/j.1745-4603.2008.00161.x.
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). Yoghurts were compressed with a 20 mm diameter cylindrical probe (36R) up to 10mm depth at a constant speed (1 mm/s). Gel firmness is characterized as maximum force (N) on time force curve compression. This parameter was evaluated in triplicate for each trial on 1st, 14th and 28th days of storage period.

Apparent viscosity

Apparent viscosity was evaluated at 5 °C utilizing a Rotational Viscometer Microprocessor (Q860M21, Quimis®, Sao Paulo, SP, Brazil) with spindle number 4. The spindle was rotated at 20 rpm. Readings were recorded at the 30th second of the measurement period and expressed as millipascal seconds (mPa.s), as described by BALTHAZAR et al. (2015BALTHAZAR, C. F., et al. Sensory evaluation of ovine milk yoghurt with inulin addition. International Journal of Dairy Technology, v.68, n.2, p.281-290. 2015. Available from: <Available from: http://onlinelibrary.wiley.com/doi/10.1111/1471-0307.12189/abstract >. Accessed: Feb. 22, 2018. doi: 10.1111/1471-0307.12189.
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). Apparent viscosity was performed in triplicate on 1st, 14th and 28th days of the storage period for each trial.

Water-holding capacity

Water-holding capacity (WHC) was analyzed as described by REMEUF et al. (2003REMEUF, F., et al. Preliminary observations on the effects of milk fortification and heating on microstructure and physical properties of stirred yogurt. International Dairy Journal, v.13, n.9, p.773-782. 2003. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S095869460300092X >. Accessed: Feb. 26, 2018. doi: 10.1016/S0958-6946(03)00092-X.
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) with slight modifications. Yoghurt (Y) samples (20 g) were centrifuged (Hermle Z 360K, Wehingen, Germany) for 20 min at 4,500 × g and 4 °C. Expelled whey (EW) was removed and weighed. WHC was obtained in triplicate for each trial on 1st, 14th and 28th days of the storage period. The WHC was calculated as: WHC (%)=100(Y - WE)/Y.

Syneresis index

Yoghurts syneresis index were performed according to DANNENBERG and KESSLER H (1988DANNENBERG, F.; G. KESSLER H. Effect of denaturation of beta-lactoglobulin on texture properties of set-style nonfat yoghurt. 2. Firmness and flow properties. [English]. Milchwissenschaft. 1988. Available from: <Available from: http://agris.fao.org/agris-search/search.do?recordID=DE19890125385 >. Accessed: Feb. 22, 2018.
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) with slight modifications and expressed as whey percentage weight separated from the gel. A yoghurt portion was removed with an ice cream scoop (d=45 mm), in order to obtain approximately 29 g of hemispherical sample, and the flat side was placed onto a test sieve (mesh width 0.5 mm). The whey volume (mL) drained off was measured at 10 °C after 2 h. Syneresis index was evaluated in triplicate for each trial on 1st, 14th and 28th days of the storage period.

Microstructural analysis

Microstructural analysis was performed according to the method described by DOMAGAŁA et al. (2013DOMAGAŁA, J., et al. The effect of transglutaminase concentration on the texture, syneresis and microstructure of set-type goat’s milk yoghurt during the storage period. Small Ruminant Research, v.112, n.1, p.154-161. 2013. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0921448812005202 >. Accessed: Feb. 22, 2018. doi: 10.1016/j.smallrumres.2012.12.003.
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) with slight modifications. Yoghurt samples microstructural characteristics were investigated using the scanning electron microscopy (SEM). Samples of 1 cm3 of each yoghurt were fixed overnight in 2.5% glutaraldehyde and 0.1 M potassium cacodylate buffer at 4 ºC, rinsed (three times) with ultrafiltered water for 10 min, post-fixed overnight in 2% osmium tetroxide. Further, the fixed and post-fixed yoghurt samples were dehydrated with ethanol solutions (30 %, 50 %, 70 % and 95 %) for 10 min each, and three times on 100% ethanol. An additional drying step using the critical point method with liquid carbon dioxide (Bal-Tec SCD 050, Balzers, Liechtenstein) was executed. Dry yoghurt samples were stuck on aluminum stubs with silver epoxy and gold-coated under vacuum using a sputter coater (Bal-Tec SCD 050, Balzers, Liechtenstein). Yoghurt microstructures were examined by SEM (Zeiss evo ma10, Oberkochen, Germany). Six fields were observed for each sample.

Statistical analysis

Analysis of variance (ANOVA) was used in order to assess the influence of species on yoghurt chemical and textural properties. Tukey’s test was utilized to determine differences among means at 0.05 of significance level. Data were analyzed using XLSTAT version 2012.6.08 (Addinsoft, Paris, France).

RESULTS AND DISCUSSION:

Bacteriological analysis

The bacteria count of yoghurts manufactured in the 1st and 28th day of the storage period utilizing milk from different species are presented in table 1. Bacteriological counts during storage period after fermentation characterized the fermented milk as yoghurt, according to Codex Alimentarius (2010), in which the minimum count required is 7.00 log CFU/g. The viability of great amount of lactic acid bacteria in yoghurts has been correlated with several benefits for consumer’s health, such as high lactose tolerance, intestinal microflora benefic balance, antimicrobial activity and immune system stimulation (BIROLLO et al., 2000BIROLLO, G. A., et al. Viability of lactic acid microflora in different types of yoghurt. Food Research International, v.33, n.9, p.799-805. 2000. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0963996900001010 >. Accessed: Feb. 22, 2018. doi: 10.1016/S0963-9969(00)00101-0.
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). A decrease on bacterial counts was observed in the present study at the end of the storage period, by results reported by BEAL et al. (1999BEAL, C., et al. Combined effects of culture conditions and storage time on acidification and viscosity of stirred yogurt. Journal of Dairy Science, v.82, n.4, p.673-681. 1999. Available from: <Available from: http://www.journalofdairyscience.org/article/S0022-0302(99)75283-5/abstract >. Accessed: Feb. 22, 2018. doi: 10.3168/jds.S0022-0302(99)75283-5.
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), BIROLLO et al. (2000), AKALIN et al. (2004AKALIN, A. S., et al. Viability and activity of bifidobacteria in yoghurt containing fructooligosaccharide during refrigerated storage. International Journal of Food Science & Technology, v.39, n.6, p.613-621. 2004. Available from: <Available from: http://onlinelibrary.wiley.com/doi/ 10.1111/j.1365-2621.2004.00829.x/abstract >. Accessed: Feb. 22, 2018. doi: 10.1111/j.1365-2621.2004.00829.x.
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).

Table 1
Bacteria count in the 1th and 28th day of storage period of yoghurts manufactured utilizing milk from different species

Proximate composition

The proximate composition of the different raw milk species, as well as the breed of animals, substantially determines the final composition of the manufactured yogurts. Despite we have not detailed described different species raw milk composition in this research, the yogurt physical-chemical composition had already been determined and can be accessed in our research group previous publication (BALTHAZAR et al., 2015BALTHAZAR, C. F., et al. Sensory evaluation of ovine milk yoghurt with inulin addition. International Journal of Dairy Technology, v.68, n.2, p.281-290. 2015. Available from: <Available from: http://onlinelibrary.wiley.com/doi/10.1111/1471-0307.12189/abstract >. Accessed: Feb. 22, 2018. doi: 10.1111/1471-0307.12189.
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, VIANNA et al., 2017VIANA, F. S., et al. Development of new probiotic yoghurt with a mixture of cow and sheep milk: effects on physicochemical, textural and sensory analysis. Small Ruminant Research , v. 149, p. 154-162. 2017. Available from: Available from: https://www.sciencedirect.com/science/article/pii/S0921448817300366 . Accessed: Feb. 28, 2019. doi: 10.1016/j.smallrumres.2017.02.013.
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). In the present study, SY demonstrated greater (P<0.05) total solids, protein, and lipid contents than CY and GY, whereas these differences were not detected (P>0.05) between CY and GY (Table 2). Moreover, the three types of yoghurt exhibited similar (P>0.05) ash content. In general, sheep milk contains greater total solids, protein and lipid content than goat and cow milk (PARK, 2007PARK, Y. W., et al. Physico-chemical characteristics of goat and sheep milk. Small Ruminant Research, v.68, n.1, p.88-113. 2007. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0921448806002549 >. Accessed: Feb. 26, 2018. doi: 10.1016/j.smallrumres.2006.09.013.
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), which potentially reflected on the differences above.

Table 2
Proximate composition of yoghurts manufactured utilizing milk from different species.

In accordance with the present research results, (ERKAYA & ŞENGÜL, 2012ERKAYA, T.; M. ŞENGÜL. A comparative study on some quality properties and mineral contents of yoghurts produced from different type of milks. Kafkas Universitesi Veteriner Fakultesi Dergisi, v.18, n.2. 2012. Available from: <Available from: http://vetdergikafkas.org/uploads/pdf/pdf_KVFD_1100.pdf >. Accessed: Feb. 22, 2018. doi: 10.9775/kvfd.2011.5498.
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) studied yoghurts produced utilizing milk from different species and observed greater total solids, protein and lipid content in sheep milk yoghurt when compared to cow and goat milk yoghurts. GÜLER & SANAL (2009GÜLER, Z.; H. SANAL. The essential mineral concentration of Torba yoghurts and their wheys compared with yoghurt made with cows’, ewes’ and goats’ milks. International Journal of Food Sciences and Nutrition, v.60, n.2, p.153-164. 2009. Available from: <Available from: http://www.ncbi.nlm.nih.gov/pubmed/18608571 >. Accessed: Feb. 22, 2018. doi: 10.1080/09637480701625580.
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) also documented greater protein and lipid content in sheep milk yoghurt than cow and goat milk yoghurts; moreover, chemical composition of yoghurt produced with cow milk was similar to goat counterpart. In addition, GÜLER & GÜRSOY-BALCI (2011)GÜLER, Z.; A. C. GÜRSOY-BALCI. Evaluation of volatile compounds and free fatty acids in set types yogurts made of ewes’, goats’ milk and their mixture using two different commercial starter cultures during refrigerated storage. Food Chemistry, v.127, n.3, p.1065-1071. 2011. Available from: <Available from: http://www.ncbi.nlm.nih.gov/pubmed/25214097 >. Accessed: Feb. 22, 2018. doi: 10.1016/j.foodchem.2011.01.090.
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produced yoghurts using sheep and goat milk and their mixture. These authors also observed that sheep milk yoghurt obtained greater values of total solids, protein and lipid than goat milk yoghurt.

Carbohydrates profile

Carbohydrates contents values from SY, CY and GY are presented in table 3. On the first day (day 1) of storage while CY and GY demonstrated greater (P<0.05) lactose content than SY whereas, SY exhibited the greatest (P<0.05) galactose content; after day 7 of storage, no difference (P>0.05) on the aforementioned molecule’s contents was observed among all yoghurts. Furthermore, during the storage period, the lactose and galactose content values in SY remained similar (P>0.05) whereas, on CY and GY the lactose content decreased (P<0.05), and the galactose values increased (P<0.05). In contrast, the SY and CY glucose content were detected just at the beginning of storage, while GY demonstrated fluctuations (P<0.05) during the yoghurt storage period.

Table 3
Carbohydrates and organic acids content values of yoghurts manufactured utilizing milk from different species.

Lactose is the major carbohydrate in goat, sheep and cow milk and is composed by glucose and galactose monomers (PEREIRA DA COSTA & CONTE-JUNIOR, 2015 PEREIRA DA COSTA, M.; C. A. CONTE-JUNIOR. Chromatographic methods for the determination of carbohydrates and organic acids in foods of animal origin. Comprehensive Reviews in Food Science and Food Safety, v.14, n.5, p.586-600. 2015. Available from: <Available from: http://onlinelibrary.wiley.com/doi/10.1111/1541-4337.12148/abstract >. Feb. 26, 2018. doi: 10.1111/1541-4337.12148.
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). In general, sheep and cow milk types contain similar lactose levels (Park et al. 2007PARK, Y. W., et al. Physico-chemical characteristics of goat and sheep milk. Small Ruminant Research, v.68, n.1, p.88-113. 2007. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0921448806002549 >. Accessed: Feb. 26, 2018. doi: 10.1016/j.smallrumres.2006.09.013.
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), which are greater than goat milk (MAYER & FIECHTER, 2012MAYER, H. K.; G. FIECHTER. Physical and chemical characteristics of sheep and goat milk in Austria. International Dairy Journal, v.24, n.2, p.57-63. 2012. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0958694611002573 >. Accessed: Feb. 22, 2018. doi: 10.1016/j.idairyj.2011.10.012.
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). Greater lactose content in milk can positively influence the yoghurt texture as due to the ability of the starter microorganisms to produce an exopolysaccharide (EPS) from this carbohydrate (TAMIME & ROBINSON, 2007TAMIME, A. Y.; R. K. ROBINSON. Tamime and Robinson’s Yoghurt, Third Edition: Science and Technology. Cambridge: Woodhead Publishing. 2007. 808 p.). In this context, the lower values of lactose with greater content of galactose on SY than on CY and GY, at the beginning of storage, is potentially due to the hydrolysis of lactose into galactose by starter microorganisms during the fermentation period. Conversely, CY and GY demonstrated a slight decrease, which can be explained by this molecule consumption during storage with the release of galactose from lactose hydrolysis (FARNWORTH, 2008FARNWORTH, E. Handbook of fermented functional food. Broken Sound Parkway, New York: CRC Press. 2008.). The GY glucose content fluctuations during storage period can be attributed to glucose consumption (KAMINARIDES et al., 2007KAMINARIDES, S., et al. Comparison of the characteristics of set type yoghurt made from ovine milk of different fat content. International Journal of Food Science & Technology, v.42, n.9, p.1019-1028. 2007. Available from: <Available from: http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2621.2006.01320.x/abstract >. Accessed: Feb. 22, 2018. doi: 10.1111/j.1365-2621.2006.01320.x.
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) and through lactose conversion by yoghurt microorganisms (VÉNICA et al., 2014VÉNICA, C. I., et al. Organic acids profiles in lactose-hydrolyzed yogurt with different matrix composition. Dairy Science & Technology, v.94, n.6, p.561-580. 2014. Available from: <Available from: https://link.springer.com/article/10.1007/s13594-014-0180-7 >. Accessed: Feb. 27, 2018. doi: 10.1007/s13594-014-0180-7.
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). Similar to our results, (DOMAGAŁA, 2009DOMAGAŁA, J. Instrumental texture, syneresis and microstructure of yoghurts prepared from goat, cow and sheep milk. International Journal of Food Properties, v.12, n.3, p.605-615. 2009. Available from: <Available from: https://doi.org/10.1080/10942910801992934 >. Accessed: Feb. 22, 2018. doi: 10.1080/10942910801992934.
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) documented that lactose content values in cow and goat milk yoghurts were similar. Moreover, in partial agreement with the present research, (VÉNICA et al., 2014VÉNICA, C. I., et al. Organic acids profiles in lactose-hydrolyzed yogurt with different matrix composition. Dairy Science & Technology, v.94, n.6, p.561-580. 2014. Available from: <Available from: https://link.springer.com/article/10.1007/s13594-014-0180-7 >. Accessed: Feb. 27, 2018. doi: 10.1007/s13594-014-0180-7.
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) reported an increase in galactose and lactic acid content, with a simultaneous decline in lactose content in fermented products manufactured with sheep and cow milk.

Organic acids profile

Organic acids values from yoghurts manufactured utilizing SM, CM and GM are exhibited in table 3. CY exhibited the lowest (P<0.05) lactic acid content, and GY the greatest (P<0.05) values from day 21 of storage. In addition, all yoghurt treatments demonstrated a lactic acid content increase (P<0.05) during the yoghurt storage period. In general, SY exhibited greater (P<0.05) citric and formic acid contents than CY and GY. Moreover; although, SY and CY citric acid content values exhibited an increase (P<0.05), GY did not exhibit (P>0.05) difference during the storage period. Furthermore, formic acid content generally remained similar (P>0.05) in all yoghurt treatments during the storage period.

Lactic acid is the major final product of lactic acid bacteria fermentative energy metabolism and its increase in yoghurts is common after refrigerated storage (DE ANCOS et al., 2000DE ANCOS, B., et al. Characteristics of stirred low-fat yoghurt as affected by high pressure. International Dairy Journal, v.10, n.1, p.105-111. 2000. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0958694600000212 >. Accessed: Feb. 22, 2018. doi: 10.1016/S0958-6946(00)00021-2.
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) due to the lactose utilization by starter cultures (TAMIME & ROBINSON, 2007TAMIME, A. Y.; R. K. ROBINSON. Tamime and Robinson’s Yoghurt, Third Edition: Science and Technology. Cambridge: Woodhead Publishing. 2007. 808 p.), which explains the slight lactose decrease and lactic acid increase observed in the present research. According to (GRANATA & MORR, 1996GRANATA, L. A.; C. V. MORR. Improved acid, flavor and volatile compound production in a high protein and fiber soymilk yogurt-like product. Journal of Food Science, v.61, n.2, p.331-336. 1996. Available from: <Available from: http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2621.1996.tb14188.x/abstract >. Accessed: Feb. 22, 2018. doi: 10.1111/j.1365-2621.1996.tb14188.x.
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), the adequate lactic acid amount can positively contribute with yoghurt texture leading to a minimum syneresis index during the storage period. In the present research, GY obtained the greatest acid lactic content at the end of yoghurt storage (21th and 28th storage days) (Table 3), which potentially lead to an effect on the aforementioned yoghurt texture. Although, SY lactic acid content was similar to GY between the 1st and 14th storage day, SY obtained the greatest total solids and protein content (Table 2). Therefore the lactic acid content alone may not affect SY textural properties. Citric acid is the most abundant organic acid present in raw milk (TORMO & IZCO, 2004TORMO, M.; J. M. IZCO. Alternative reversed-phase high-performance liquid chromatography method to analyse organic acids in dairy products. Journal of Chromatography A, v.1033, n.2, p.305-310. 2004. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0021967304001311 >. Accessed: Feb. 26, 2018. doi: 10.1016/j.chroma.2004.01.043.
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) thus, the observed citric acid content values increase indicates negligible citric acid utilization by starter cultures during storage (ADHIKARI et al., 2002ADHIKARI, K., et al. Changes in the profile of organic acids in plain set and Stirred Yogurts During Manufacture and Refrigerated Storage1. Journal of Food Quality, v.25, n.5, p.435-451. 2002. Available from: <Available from: http://onlinelibrary.wiley.com/doi/10.1111/j.1745-4557.2002.tb01038.x/abstract >. Accessed: Feb. 22, 2018. doi: 10.1111/j.1745-4557.2002.tb01038.x.
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).

In agreement with results reported in the present study, KAMINARIDES et al. (2007KAMINARIDES, S., et al. Comparison of the characteristics of set type yoghurt made from ovine milk of different fat content. International Journal of Food Science & Technology, v.42, n.9, p.1019-1028. 2007. Available from: <Available from: http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2621.2006.01320.x/abstract >. Accessed: Feb. 22, 2018. doi: 10.1111/j.1365-2621.2006.01320.x.
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) concluded that sheep milk yoghurt with elevated fat content obtained greater texture scores such as firmness and lower syneresis index than other low- regular-fat treatments. The concentration of lactic acid in the aforementioned yoghurt was lower than those produced with different fat content. Thus the absence of textural defects in that study can be due to the sheep milk high total solids and low lactic acid content. In agreement with the present research, HERRERO & REQUENA (2006HERRERO, A. M.; T. REQUENA. The effect of supplementing goats milk with whey protein concentrate on textural properties of set-type yoghurt. International Journal of Food Science & Technology, v.41, n.1, p.87-92. 2006. Available from: <Available from: http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2621.2005.01045.x/abstract >. Accessed: Feb. 22, 2018. doi: 10.1111/j.1365-2621.2005.01045.x.
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) evaluated the effect of supplementing goat milk with whey protein concentrate (WPC) on set-type yoghurt textural properties and reported that WPC increases the lactic acid content.

Analysis of pH and titratable acidity

Yoghurt pH and TA values from different species during storage period are exhibited in table 4. The SY, CY, and GY did not demonstrate (P>0.05) difference among pH values. When compared day 1 and 28 of the storage period CY exhibited a decrease (P<0.05) on the pH values. In addition, milk from different species affected (P<0.05) yoghurt TA; SY values were greater (P<0.05) than CY and GY. Also, during the storage period while the TA values of SY increased (P<0.05) CY and GY were not affected (P>0.05).

Table 4
Values of pH and titratable acidity of yoghurts manufactured utilizing milk from different species.

The observed pH results were expected based on the usual yoghurt pH decrease during storage period (LUCEY, 2004LUCEY, J. A. Cultured dairy products: an overview of their gelation and texture properties. International Journal of Dairy Technology, v.57, n.2-3, p.77-84. 2004. Available from: <Available from: http://onlinelibrary.wiley.com/doi/10.1111/j.1471-0307.2004.00142.x/abstract >. Accessed: Feb. 22, 2018. doi: 10.1111/j.1471-0307.2004.00142.x.
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). The slight TA increase and pH decrease observed during storage period could be due to lactic acid production through lactose hydrolysis promoted by starter culture and lactic acid bacteria (LOURENS-HATTINGH & VILJOEN, 2001LOURENS-HATTINGH, A.; B. C. VILJOEN. Yogurt as probiotic carrier food. International Dairy Journal, v.11, n.1, p.1-17. 2001. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S095869460100036X >. Accessed: Feb. 22, 2018. doi: 10.1016/S0958-6946(01)00036-X.
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; KAILASAPATHY, 2006KAILASAPATHY, K. Survival of free and encapsulated probiotic bacteria and their effect on the sensory properties of yoghurt. LWT - Food Science and Technology, v.39, n.10, p.1221-1227. 2006. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0023643805001660 >. Accessed: Feb. 22, 2018. doi: 10.1016/j.lwt.2005.07.013.
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). Nevertheless, the observed pH decreases on CY samples at the 28th day of storage is potentially due to the lower buffering capacity of cow milk than goat (PARK et al., 2007PARK, Y. W., et al. Physico-chemical characteristics of goat and sheep milk. Small Ruminant Research, v.68, n.1, p.88-113. 2007. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0921448806002549 >. Accessed: Feb. 26, 2018. doi: 10.1016/j.smallrumres.2006.09.013.
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) and sheep counterparts. Moreover, the observed increase of TA on SY can be due to greater buffering capacity associated with greater mineral, protein and dissolved CO2 content than cow and goat milks (SALAÜN et al., 2005SALAÜN, F., et al. Buffering capacity of dairy products. International Dairy Journal, v.15, n.2, p.95-109. 2005. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0958694604001487 >. Accessed: Feb. 26, 2018. doi: 10.1016/j.idairyj.2004.06.007.
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). Consequently, it leads to a greater alkali solution volume during titration step.

In agreement with the present research, DOMAGAŁA (2009DOMAGAŁA, J. Instrumental texture, syneresis and microstructure of yoghurts prepared from goat, cow and sheep milk. International Journal of Food Properties, v.12, n.3, p.605-615. 2009. Available from: <Available from: https://doi.org/10.1080/10942910801992934 >. Accessed: Feb. 22, 2018. doi: 10.1080/10942910801992934.
https://doi.org/10.1080/1094291080199293...
), ERKAYA & ŞENGÜL (2012ERKAYA, T.; M. ŞENGÜL. A comparative study on some quality properties and mineral contents of yoghurts produced from different type of milks. Kafkas Universitesi Veteriner Fakultesi Dergisi, v.18, n.2. 2012. Available from: <Available from: http://vetdergikafkas.org/uploads/pdf/pdf_KVFD_1100.pdf >. Accessed: Feb. 22, 2018. doi: 10.9775/kvfd.2011.5498.
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) reported that sheep dairy product (milk and yoghurt, respectively) exhibited greater TA values than goat and cow counterparts, demonstrating that the effect on this parameter is specie-specific. Furthermore, ERKAYA & ŞENGÜL (2012)ERKAYA, T.; M. ŞENGÜL. A comparative study on some quality properties and mineral contents of yoghurts produced from different type of milks. Kafkas Universitesi Veteriner Fakultesi Dergisi, v.18, n.2. 2012. Available from: <Available from: http://vetdergikafkas.org/uploads/pdf/pdf_KVFD_1100.pdf >. Accessed: Feb. 22, 2018. doi: 10.9775/kvfd.2011.5498.
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documented similar pH values for goat and sheep milk yoghurts, and the pH decrease associated with an increase on TA values on yoghurt from different species during storage is in accordance with other studies using cow (MATARAGAS et al., 2011MATARAGAS, M., et al. Quantifying the spoilage and shelf-life of yoghurt with fruits. Food Microbiology, v.28, n.3, p.611-616. 2011. Available from: <Available from: http://www.ncbi.nlm.nih.gov/pubmed/21356472 >. Accessed: Feb. 22, 2018. doi: 10.1016/j.fm.2010.11.009.
http://www.ncbi.nlm.nih.gov/pubmed/21356...
), buffalo (ERKAYA & ŞENGÜL, 2012ERKAYA, T.; M. ŞENGÜL. A comparative study on some quality properties and mineral contents of yoghurts produced from different type of milks. Kafkas Universitesi Veteriner Fakultesi Dergisi, v.18, n.2. 2012. Available from: <Available from: http://vetdergikafkas.org/uploads/pdf/pdf_KVFD_1100.pdf >. Accessed: Feb. 22, 2018. doi: 10.9775/kvfd.2011.5498.
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), sheep and goat (GÜLER & GÜRSOY-BALCI, 2011LE, T. T., et al. Physical properties and microstructure of yoghurt enriched with milk fat globule membrane material. International Dairy Journal, v.21, n.10, p.798-805. 2011. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0958694611001166 >. Accessed: Feb. 22, 2018. doi: 10.1016/j.idairyj.2011.04.015.
http://www.sciencedirect.com/science/art...
; ERKAYA & ŞENGÜL, 2012ERKAYA, T.; M. ŞENGÜL. A comparative study on some quality properties and mineral contents of yoghurts produced from different type of milks. Kafkas Universitesi Veteriner Fakultesi Dergisi, v.18, n.2. 2012. Available from: <Available from: http://vetdergikafkas.org/uploads/pdf/pdf_KVFD_1100.pdf >. Accessed: Feb. 22, 2018. doi: 10.9775/kvfd.2011.5498.
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) milk.

Firmness

Firmness, apparent viscosity, WHC, and syneresis from yoghurts produced utilizing milk from three different species (sheep, cow, and goat) are presented in table 5. The SY were firmer (P<0.05) than CY and GY during all storage period. Moreover, on day 14 and 28 of the storage period, CY firmness was greater (P<0.05) than GY. In addition, the storage period only affected (P<0.05) GY, demonstrating a decrease in textural quality in this type of yoghurt.

Table 5
Textural properties of yoghurts manufactured utilizing milk from different species.

Firmness is considered one of the main textural parameters for yoghurt acceptability (HARTE et al., 2007HARTE, F., et al. Yield stress for initial firmness determination on yogurt. Journal of Food Engineering, v.80, n.3, p.990-995. 2007. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0260877406005188 >. Accessed: Feb. 22, 2018. doi: 10.1016/j.jfoodeng.2006.06.027.
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). During coagulation step on yoghurt manufacturing, destabilized casein micelles and calcium-phosphate bonds form a network, which in turn entraps fat and other solids (COSTA et al., 2015bCOSTA, M. P., et al. Cupuassu (Theobroma grandiflorum) pulp, probiotic, and prebiotic: Influence on color, apparent viscosity, and texture of goat milk yogurts. Journal of Dairy Science, v.98, n.9, p.5995-6003. 2015b. Available from: <Available from: http://www.ncbi.nlm.nih.gov/pubmed/26188580 >. Accessed: Feb. 22, 2018. doi: 10.3168/jds.2015-9738.
http://www.ncbi.nlm.nih.gov/pubmed/26188...
). The speed of casein network formation is directly influenced by protein amount, mainly casein content, resulting in greater aggregation rate with firmer curd development (DIMASSI et al., 2005DIMASSI, O., et al. Cheese production potential of milk of Dahlem Cashmere goats from a rheological point of view. Small ruminant research : the journal of the International Goat Association. 2005. Available from: <Available from: http://agris.fao.org/agris-search/search.do?recordID=US201301009374 >. Accessed: Feb. 22, 2018. doi: https://doi.org/10.1016/j.smallrumres.2004.05.003
http://agris.fao.org/agris-search/search...
). Differences on total solids content among milk from different species affect yoghurt curd firmness (PARK et al., 2007PARK, Y. W., et al. Physico-chemical characteristics of goat and sheep milk. Small Ruminant Research, v.68, n.1, p.88-113. 2007. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0921448806002549 >. Accessed: Feb. 26, 2018. doi: 10.1016/j.smallrumres.2006.09.013.
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), which can be evidenced in SY firmness (Table 5) with greater (P<0.05) total solids and protein content (Table 2) when compared with the other two yoghurt types studied.

Furthermore, MARTÍN-DIANA et al. (2003MARTÍN-DIANA, A. B., et al. Development of a fermented goat’s milk containing probiotic bacteria. International Dairy Journal, v.13, n.10, p.827-833. 2003. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0958694603001171 >. Accessed: Feb. 22, 2018. doi: 10.1016/S0958-6946(03)00117-1.
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) demonstrated that firmness can also be influenced by milk casein content and micelle structure from each species. According to these authors; although, total solids content for cow and goat milk were similar, yoghurts produced with goat milk tends to be less firm than cow milk yoghurt; in the present study; although, GY and CY demonstrated similar (P>0.05) proximate composition values (Table 2), the first one was firmer (P<0.05) than the latter (Table 5). In addition, AND & GUO (2006AND, J. L.; M. GUO. Effects of polymerized whey proteins on consistency and water-holding properties of goat’s milk yogurt. Journal of Food Science, v.71, n.1, p.C34-C38. 2006. Available from: <Available from: http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2621.2006.tb12385.x/abstract >. Accessed: Feb. 22, 2018. doi: 10.1111/j.1365-2621.2006.tb12385.x.
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) reported that goat milk exhibits less αs1-casein content than cow milk which potentially explains the less consistency on GY.

In agreement with observed firmness results, DOMAGAŁA (2008DOMAGAŁA, J. Sensory evaluation and rheological properties of yoghurts prepared from goat, cow and sheep milk. Electronic journal of polish agricultural universities, v.11, n.3. 2008. Available from: <Available from: http://www.ejpau.media.pl/volume11/issue3/art-04.html >. Accessed: Accessed: Feb. 22, 2018.
http://www.ejpau.media.pl/volume11/issue...
), ZUBEIR et al. (2012ZUBEIR, I. E. M. E., et al. The processing properties, chemical characteristics and acceptability of yoghurt made from non bovine milks. Livestock Research for Rural Development, v.24, n.3. 2012. Available from: <Available from: http://www.lrrd.org/lrrd24/3/zube24050.htm >. Accessed: Feb. 26, 2018.
http://www.lrrd.org/lrrd24/3/zube24050.h...
) demonstrated that sheep milk yoghurt was firmer than goat milk yoghurt. Moreover, DOMAGAŁA (2009)DOMAGAŁA, J. Instrumental texture, syneresis and microstructure of yoghurts prepared from goat, cow and sheep milk. International Journal of Food Properties, v.12, n.3, p.605-615. 2009. Available from: <Available from: https://doi.org/10.1080/10942910801992934 >. Accessed: Feb. 22, 2018. doi: 10.1080/10942910801992934.
https://doi.org/10.1080/1094291080199293...
evaluated different textural parameters, such as hardness, adhesiveness and extrusion force among sheep, cow and goat milk yoghurts and demonstrated that yoghurts produced from goat milk exhibited the lowest values of textural parameters whereas, sheep milk yoghurts, the greatest ones; indicating that total solids and protein content can be considered important parameters to determine final product textural characteristics. In partial agreement with the present study, AMATAYAKUL et al. (2006AMATAYAKUL, T., et al. Physical characteristics of set yoghurt made with altered casein to whey protein ratios and EPS-producing starter cultures at 9 and 14% total solids. Food Hydrocolloids, v.20, n.2, p.314-324. 2006. Available from: <Available from: http://www.sciencedirect.com /science/article/pii/S0268005X05001050 >. Accessed: Feb. 22, 2018. doi: 10.1016/j.foodhyd.2005.02.015.
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) investigated firmness of set-yoghurts produced with different casein to whey ratios, as well as total solids content, and observed that the firmness did not change during storage. Additionally, KATSIARI et al. (2002KATSIARI, M. C., et al. Manufacture of yoghurt from stored frozen sheep’s milk. Food Chemistry, v.77, n.4, p.413-420. 2002. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0308814601003673 >. Accessed: Feb. 22, 2018. doi: 10.1016/S0308-8146(01)00367-3.
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) evaluated the effects of long-term deep-frozen storage on yoghurt characteristics and demonstrated that during cold storage, sheep milk yoghurt firmness slightly increased.

Apparent viscosity

This research demonstrated that apparent viscosity parameter was affected (P<0.05) by type of milk (different species) used to produce yoghurts. During all the storage period analyzed, GY obtained the lowest (P<0.05) apparent viscosity, whereas SY exhibited the greatest (P<0.05) values at days 14 and 28 of storage. In addition, the storage period did not affect (P>0.05) this parameter’s values during storage period for all yoghurt types.

Variations on apparent viscosity results observed in the present study can be attributed to differences in total solids and protein content among milk types (JUMAH et al., 2001JUMAH, R. Y., et al. Effect of milk source on the rheological properties of yogurt during the gelation process. International Journal of Dairy Technology, v.54, n.3, p.89-93. 2001. Available from: <Available from: http://onlinelibrary.wiley.com/doi/10.1046/j.1364-727x.2001.00012.x/abstract >. Accessed: Feb. 22, 2018. doi: 10.1046/j.1364-727x.2001.00012.x.
http://onlinelibrary.wiley.com/doi/10.10...
; MARTÍN-DIANA et al., 2003MARTÍN-DIANA, A. B., et al. Development of a fermented goat’s milk containing probiotic bacteria. International Dairy Journal, v.13, n.10, p.827-833. 2003. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0958694603001171 >. Accessed: Feb. 22, 2018. doi: 10.1016/S0958-6946(03)00117-1.
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). Usually, yoghurt produced with cow and goat milk require fortification in order to improve total solids content and consequently yoghurt viscosity (REMEUF et al., 2003REMEUF, F., et al. Preliminary observations on the effects of milk fortification and heating on microstructure and physical properties of stirred yogurt. International Dairy Journal, v.13, n.9, p.773-782. 2003. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S095869460300092X >. Accessed: Feb. 26, 2018. doi: 10.1016/S0958-6946(03)00092-X.
http://www.sciencedirect.com/science/art...
; HERRERO & REQUENA, 2006HERRERO, A. M.; T. REQUENA. The effect of supplementing goats milk with whey protein concentrate on textural properties of set-type yoghurt. International Journal of Food Science & Technology, v.41, n.1, p.87-92. 2006. Available from: <Available from: http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2621.2005.01045.x/abstract >. Accessed: Feb. 22, 2018. doi: 10.1111/j.1365-2621.2005.01045.x.
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) as sheep milk yoghurt already contains high total solids content, the fortification step is not required (BOYAZOGLU & MORAND-FEHR, 2001BOYAZOGLU, J.; P. MORAND-FEHR. Mediterranean dairy sheep and goat products and their quality. A critical review. Small Ruminant Research: The Journal of the International Goat Association, v.40, n.1, p.1-11. 2001. Available from: <Available from: http://www.ncbi.nlm.nih.gov/pubmed/11259871 >. Accessed: Feb. 22, 2018. doi: https://doi.org/10.1016/S0921-4488(00)00203-0
http://www.ncbi.nlm.nih.gov/pubmed/11259...
). In accordance with aforementioned results, (KÜÇÜKÇETIN et al., 2011KÜÇÜKÇETIN, A., et al. Graininess and roughness of stirred yoghurt made with goat’s, cow’s or a mixture of goat’s and cow’s milk. Small Ruminant Research, v.96, n.2, p.173-177. 2011. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0921448810003226 >. Accessed: Feb. 22, 2018. doi: 10.1016/j.smallrumres.2010.12.003.
http://www.sciencedirect.com/science/art...
; ERKAYA & ŞENGÜL, 2012ERKAYA, T.; M. ŞENGÜL. A comparative study on some quality properties and mineral contents of yoghurts produced from different type of milks. Kafkas Universitesi Veteriner Fakultesi Dergisi, v.18, n.2. 2012. Available from: <Available from: http://vetdergikafkas.org/uploads/pdf/pdf_KVFD_1100.pdf >. Accessed: Feb. 22, 2018. doi: 10.9775/kvfd.2011.5498.
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; WANG et al., 2012WANG, W., et al. Consistency, microstructure and probiotic survivability of goats’ milk yoghurt using polymerized whey protein as a co-thickening agent. International Dairy Journal, v.24, n.2, p.113-119. 2012. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0958694611002214 >. Accessed: Feb. 26, 2018. doi: 10.1016/j.idairyj.2011.09.007.
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) evaluated apparent viscosity among yoghurt samples produced from different types of milk (goat, cow, and their mixture), and observed that yoghurt viscosity obtained from goat milk was lower than cow milk yoghurt and their mixtures.

Water-holding capacity

During all storage period analyzed, SY exhibited the greatest (P<0.05) WHC values, whereas GY the lowest (P<0.05) ones. Furthermore, storage period did not influence (P>0.05) this parameter. Total solids and protein content directly affected WHC, potentially due to greater milk proteins content which increases yoghurt gel network density, and consequently the WHC (KRASAEKOOPT et al., 2004KRASAEKOOPT, W., et al. Comparison of texture of yogurt made from conventionally treated milk and uht milk fortified with low-heat skim milk powder. Journal of Food Science, v.69, n.6, p.E276-E280. 2004. Available from: <Available from: http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2621.2004.tb10998.x/abstract >. Accessed: Feb. 22, 2018. doi: 10.1111/j.1365-2621.2004.tb10998.x.
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). SODINI et al. (2004SODINI, I., et al. The relative effect of milk base, starter, and process on yogurt texture: a review. Critical Reviews in Food Science and Nutrition, v.44, n.2, p.113-137. 2004. Available from: <Available from: http://www.ncbi.nlm.nih.gov/pubmed/15116758 >. Accessed: Feb. 26, 2018. doi: 10.1080/10408690490424793.
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) reported that an increase in casein concentration can favor its micelles interaction as well as, leading to decrease of matrix pore dimensions and an increase of its density. In addition; although, GY and CY demonstrated similar total solids and protein contents (Table 2), GY exhibited lower (P<0.05) WHC values, which can be explained by differences on micelle hydration between these aforementioned types of milk (goat milk is less hydrated than cow milk) (PARK et al., 2007PARK, Y. W., et al. Physico-chemical characteristics of goat and sheep milk. Small Ruminant Research, v.68, n.1, p.88-113. 2007. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0921448806002549 >. Accessed: Feb. 26, 2018. doi: 10.1016/j.smallrumres.2006.09.013.
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).

LE et al. (2011LE, T. T., et al. Physical properties and microstructure of yoghurt enriched with milk fat globule membrane material. International Dairy Journal, v.21, n.10, p.798-805. 2011. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0958694611001166 >. Accessed: Feb. 22, 2018. doi: 10.1016/j.idairyj.2011.04.015.
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) compared yoghurts with a similar amount of dry solids content containing an increased milk fat globule membrane material concentration and observed a WHC improvement due to an increase in total solids content. Moreover, KÜÇÜKÇETIN et al. (2011KÜÇÜKÇETIN, A., et al. Graininess and roughness of stirred yoghurt made with goat’s, cow’s or a mixture of goat’s and cow’s milk. Small Ruminant Research, v.96, n.2, p.173-177. 2011. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0921448810003226 >. Accessed: Feb. 22, 2018. doi: 10.1016/j.smallrumres.2010.12.003.
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) observed that yoghurt produced with goat milk obtained lower WHC than yoghurts manufactured utilizing cow milk. In addition, MALEK et al. (2001MALEK, A., et al. Sensory properties and consumer acceptance of concentrated yogurt made from cow’s, goat’s and sheep’s milk. 2001. Available from: <Available from: https://www.scienceopen.com/document?vid=c64ddd43-0d61-426e-a1da-1b21f9b04b2d >. Accessed: Feb. 22, 2018.
https://www.scienceopen.com/document?vid...
) reported that; although, yoghurts produced with cow and goat milk demonstrated similar total solids content, the former one released less water than those obtained from goat milk.

Syneresis index

The yoghurt syneresis index was (P<0.05) affected by milk type but not by storage period (P>0.05). In contrast with WHC, the lowest (P<0.05) syneresis index value was observed in SY whereas, the greatest (P<0.05) one in GY during all the storage period analyzed. Syneresis represents an important concern in yoghurt commercial manufacturing, which can lead to accumulation of whey (serum) on yoghurt gel surface, decreasing the consumer acceptance (GHASEMPOUR et al., 2012GHASEMPOUR, Z., et al. Optimisation of probiotic yoghurt production containing zedo gum. International Journal of Dairy Technology, v.65, n.1, p.118-125. 2012. Available from: <Available from: http://onlinelibrary.wiley.com/doi/10.1111/j.1471-0307.2011.00740.x/abstract >. Accessed: Feb. 22, 2018. doi: 10.1111/j.1471-0307.2011.00740.x.
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). According to AMATAYAKUL et al. (2006AMATAYAKUL, T., et al. Physical characteristics of set yoghurt made with altered casein to whey protein ratios and EPS-producing starter cultures at 9 and 14% total solids. Food Hydrocolloids, v.20, n.2, p.314-324. 2006. Available from: <Available from: http://www.sciencedirect.com /science/article/pii/S0268005X05001050 >. Accessed: Feb. 22, 2018. doi: 10.1016/j.foodhyd.2005.02.015.
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), an increase in total solids content favors syneresis decrease potentially clarifying why yoghurt samples that demonstrated the greatest total solids content, obtained the lowest syneresis index. Casein and colloidal calcium content also affect syneresis index. Thus, the greater sheep milk micelles mineralization levels than cow and goat milk (PARK et al., 2007PARK, Y. W., et al. Physico-chemical characteristics of goat and sheep milk. Small Ruminant Research, v.68, n.1, p.88-113. 2007. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0921448806002549 >. Accessed: Feb. 26, 2018. doi: 10.1016/j.smallrumres.2006.09.013.
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), may explain the SY lowest syneresis index. Furthermore, in agreement with this study, DOMAGAŁA (2009DOMAGAŁA, J. Instrumental texture, syneresis and microstructure of yoghurts prepared from goat, cow and sheep milk. International Journal of Food Properties, v.12, n.3, p.605-615. 2009. Available from: <Available from: https://doi.org/10.1080/10942910801992934 >. Accessed: Feb. 22, 2018. doi: 10.1080/10942910801992934.
https://doi.org/10.1080/1094291080199293...
), ERKAYA & ŞENGÜL, (2012ERKAYA, T.; M. ŞENGÜL. A comparative study on some quality properties and mineral contents of yoghurts produced from different type of milks. Kafkas Universitesi Veteriner Fakultesi Dergisi, v.18, n.2. 2012. Available from: <Available from: http://vetdergikafkas.org/uploads/pdf/pdf_KVFD_1100.pdf >. Accessed: Feb. 22, 2018. doi: 10.9775/kvfd.2011.5498.
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) demonstrated that yoghurts from goat milk exhibited greater syneresis index than yoghurts produced with sheep milk.

Microstructural analysis

The scanning electron micrographs obtained from yoghurts elaborated with sheep, cow and goat milk are depicted in figure 1 and 2. The figures illustrate the yoghurt protein network microstructure entrapping fat globules and void spaces (Figure 1, 2) filled with bacterial cells (Figure 2). Yoghurt consists of a network composed by clusters or chains of casein particles forming a three-dimensional matrix (PENNA et al., 2007PENNA, A. L. B., et al. High hydrostatic pressure processing on microstructure of probiotic low-fat yogurt. Food Research International, v.40, n.4, p.510-519. 2007. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0963996907000142 >. Accessed: Feb. 26, 2018. doi: 10.1016/j.foodres.2007.01.001.
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). Microstructural differences among the three yoghurt types were visualized. As depicted in figure 1, SY (Figure 1A) was characterized by a denser structure exhibiting fewer pores structure than CY (Figure 1B) and GY (Figure 1C), which in turn exhibited a more open structure. In addition, SY (Figure 2a) exhibited a more branched-structured gel and more interconnected clusters, demonstrating a very fine network composed by small and homogeneous void spaces, embedded with fat globules and bacterial cells. These observations support the strong link between yoghurt gel microstructure and textural properties. SY exhibited greater firmness, apparent viscosity and, water-holding capacity, and lower syneresis index values than CY and GY (Table 5); finer protein chains, smaller casein particles and pore sizes improves water immobilization (KRZEMINSKI et al., 2011KRZEMINSKI, A., et al. Structural properties of stirred yoghurt as influenced by whey proteins. LWT - Food Science and Technology, v.44, n.10, p.2134-2140. 2011. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0023643811001666 >. Accessed: Feb. 22, 2018. doi: 10.1016/j.lwt.2011.05.018.
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). The GY (Figure 2c) exhibited plenty of void spaces with heterogeneous size and irregular microstructure, as well as CY; however, GY presented a coarser gel structure and large clusters, suggesting differences on micelle characteristics among the three studied yoghurt types. These GY microstructural differences can be explained due to differences in casein fraction relative proportions in goat milk when compared with cow and sheep milk.

Figure 1
Scanning electron microscopy (SEM) micrographs of yoghurts manufactured with sheep milk (A), cow milk (B) and goat milk (C). Bar = 50 µm. v, void space; cs, casein, lp, lipid.

Figure 2
Scanning electron microscopy (SEM) micrographs of yoghurts produced with sheep milk (a), cow milk (b) and goat milk (c). Bar=20 µm. St, Streptococcus thermophilus; Lb, Lactobacillus delbrueckii ssp. bulgaricus; v, void space; cs, casein, lp, lipid.

TAMIME and ROBINSON (2007TAMIME, A. Y.; R. K. ROBINSON. Tamime and Robinson’s Yoghurt, Third Edition: Science and Technology. Cambridge: Woodhead Publishing. 2007. 808 p.) also reported that the porosity of yoghurt gel was more compact or denser in sheep milk yoghurt than cow counterpart. As described by PARK et al. (2007PARK, Y. W., et al. Physico-chemical characteristics of goat and sheep milk. Small Ruminant Research, v.68, n.1, p.88-113. 2007. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0921448806002549 >. Accessed: Feb. 26, 2018. doi: 10.1016/j.smallrumres.2006.09.013.
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), the casein micelle structure of cow milk differs from sheep milk in diameter, hydration and mineralization in addition to the smaller fat globule size on sheep milk than in cow counterpart potentially explain the CY weaker gel structure in comparison with SY. Furthermore, NGUYEN et al. (2014aNGUYEN, H. T. H., et al. The effect of fermentation temperature on the microstructure, physicochemical and rheological properties of probiotic buffalo yoghurt. Food and Bioprocess Technology, v.7, n.9, p.2538-2548. 2014a. Available from: <Available from: https://link.springer.com/article/10.1007/s11947-014-1278-x >. Accessed: Feb. 22, 2018. doi: 10.1007/s11947-014-1278-x.
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) reported that other parameters in addition to total solids content, such as concentration of lactose, calcium, and fat globules as well as, fat globules surface area also influence yoghurt structure and textural properties. Thus, the observed differences among CY, SY and GY are potentially attributed to differences in milk physicochemical characteristics. Moreover, caprine casein micelles contain more calcium and inorganic phosphorus, and are less solvated, less heat stable, and release β-casein more rapidly than bovine casein micelles (PARK et al., 2007). During fermentation, the decrease in pH values closer to the casein micelles isoelectric point (pH 4.6) favors the colloidal calcium phosphate solubilization, increasing hydrophobic interaction. Ultimately, causing casein micelles aggregation into a three-dimensional chain network, LUCEY (2004LUCEY, J. A. Cultured dairy products: an overview of their gelation and texture properties. International Journal of Dairy Technology, v.57, n.2-3, p.77-84. 2004. Available from: <Available from: http://onlinelibrary.wiley.com/doi/10.1111/j.1471-0307.2004.00142.x/abstract >. Accessed: Feb. 22, 2018. doi: 10.1111/j.1471-0307.2004.00142.x.
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) & (PHADUNGATH, (2005PHADUNGATH, C. The mechanism and properties of acid-coagulated milk gels. Songklanakarin Journal of Science and Technology, v.27, p.433-448. 2005. Available from: <Available from: https://www.semanticscholar.org/paper/The-mechanism-and-properties-of-acid-coagulated-Phadungath/335dfe6e3b102a74f74c7d3eb72e17d317dd76f2 >. Accessed: Feb. 26, 2018.
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) demonstrated that casein micelles play an important role in milk acid coagulation. In agreement with this research, DOMAGAŁA (2009DOMAGAŁA, J. Instrumental texture, syneresis and microstructure of yoghurts prepared from goat, cow and sheep milk. International Journal of Food Properties, v.12, n.3, p.605-615. 2009. Available from: <Available from: https://doi.org/10.1080/10942910801992934 >. Accessed: Feb. 22, 2018. doi: 10.1080/10942910801992934.
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) reported that goat milk yoghurt microstructure was more delicate, less resistant to deformation and more susceptible to syneresis than cow and sheep counterparts; sheep milk yoghurt exhibited the strongest gel matrix. Additionally, VARGAS et al. (2008VARGAS, M., et al. Physicochemical and sensory characteristics of yoghurt produced from mixtures of cows’ and goats’ milk. International Dairy Journal, v.18, n.12, p.1146-1152. 2008. Available from: <Available from: http://www.sciencedirect.com/science/article/pii/S0958694608001179 >. Accessed: Feb. 26, 2018. doi: 10.1016/j.idairyj.2008.06.007.
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) demonstrated that yoghurt formulations with 100% of goat milk were characterized by a smaller number of junction points, which led to a more open structure with larger pores and a greater number of smaller fat globules than formulations with 100% cow milk.

CONCLUSION:

The chemical parameters of yoghurts, mainly total solids, protein, lipid and lactic acid content are specie-specific. These differences potentially affected textural and microstructural yoghurt properties. The present study demonstrated a clear correlation among chemical, textural, and microstructural yoghurt parameters. Sheep milk produced yoghurt with the most desirable textural characteristics for consumer market while goat milk yoghurt exhibited the lowest attractive textural properties. In Brazil, the extensive livestock area, the large cattle farming and the popular culture of the cow milk consume are reasons why sheep’s milk yogurt is not produced on a commercial scale yet. Nevertheless, sheep milk yoghurt can be considered a suitable alternative to cow milk yoghurt, especially in states with a low level of cattle production like Rio de Janeiro.

ACKNOWLEDGEMENTS

“This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Brasil - Finance code 001”.

REFERENCES

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    CR-2018-0522.R1

Publication Dates

  • Publication in this collection
    13 June 2019
  • Date of issue
    2019

History

  • Received
    28 June 2018
  • Accepted
    29 Apr 2019
  • Reviewed
    28 May 2019
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