Microbiological Profile of Meat from Pekin Ducks During Refrigerated Storage in Air and VacuumABSTRACT
This study investigates the dynamics of spoilage microflora in duck meat packed in vacuum and air during 9 days of storage. In total, 72 duck carcasses were used in the study. Samples of meat (breasts and thighs, with or without skin) were analysed on days 1, 3, 6 and 9 after packaging in two different atmospheres, at a storage temperature of 3°C ± 1°C. Enterobacteriaceae, coliform bacteria, and E. coli, Total Viable Count, psychrotrophic microorganisms, Lactic Acid Bacteria, Pseudomonas spp. counts, and Brochothrix thermosphacta were determined. As expected, the type of sample and storage length had the greatest influence on microbiological quality (p<0.001). Lower significance (p<0.01) was observed for the place of sampling factor - i.e. duck breast or thigh. As expected, better microbiological parameters were achieved with vacuum-packed samples. The pH value increased during storage, but the increase was minimal for the vacuum-packed samples. In all the microbiological parameters monitored, the best results at the end of storage were obtained for duck breast muscles packed in vacuum.
Keywords:
Anas platyrhynchos; Duck Meat; Spoilage; Meat Microbiology; Pekin Duck
INTRODUCTION
During the last 50 years, poultry meat production worldwide has risen 10-fold to more than 100 million tons (Hakeem & Lu, 2021). China continues to be the largest producer of duck meat in the world (3 million tons annually); the main producers among European countries are France, Germany, the UK, and the Netherlands (Huda et al., 2011; Biswas et al., 2019; Hou et al., 2021). An increasing trend in the number of ducks slaughtered has been observed in recent years in Poland, which is competing with Hungary and France (Vorotnikov, 2022). In 2021, France produced 177,000 tonnes of duck meat, compared to 90,000 tonnes in Hungary, 57,000 tonnes in Poland, and 20,000 tonnes in Germany and Bulgaria (AVEC report, 2022). The global duck meat market is expected to grow at a steady pace, driven by the demand for processed and packaged food among consumers (Biswas et al., 2019). A large part of the slaughtered ducks is released for consumption chilled or frozen as whole carcasses, while the portions are placed on the market in modified atmosphere packaging or vacuum packaging.
Packaging is an important tool for food preservation, ensuring that the product is delivered to the consumer in the best condition. Packaging materials and the atmospheric conditions created inside the packaging protect the foodstuffs from chemical degradation, microbial contamination and proliferation, physical damage, and other negative effects originating from the environment (Hakeem & Lu, 2021). Packaging plays a key role in minimising meat contamination and quality deterioration issues. Various packaging systems are available for poultry meat, depending on their applications (Nauman et al., 2022).
In order to extend shelf life, preservation technologies like vacuum packaging or modified atmosphere packaging (MAP) are applied for distribution and retail sale of poultry meat and products. The combination of chilling temperatures with different types of packaging methods is used to maximise the shelf life of fresh poultry meat. Although MAP is increasingly popular, packaging in permeable stretch film (tray and overwrap format) is still in use for its cost-effectiveness. Vacuum packaging is used for tray-less packaging of frozen and fresh poultry. Vacuum skin packaging (tray and heated foil) can be used for the packaging of portions (Mangalassary, 2019). Depending on the type of atmosphere present (oxygen availability), the microflora of the packaged meat also differs. Pseudomonas spp., lactic acid bacteria, and Enterobacteriaceae together with Brochothrix thermosphacta, have been considered the dominant spoilage microorganisms in poultry meat. The presence of spoilage microflora does not usually pose a health risk to the consumer, but it brings economic losses to producers and traders (Hakeem & Lu, 2021; Nauman et al., 2022; Zouharova et al., 2023).
Since data on duck meat including microbiological quality are scarce, the aim of this experiment was to compare the shelf life of duck meat (breasts and thighs) in two different commercially available packaging methods. With regard to the different types of packaging used, the occurrence and progression of the growth of contaminating and spoilage microflora were monitored. Further details on references are available at the end of the paper.
MATERIALS AND METHODS
Characterization of the ducks
Conventional Pekin ducks of hybrid line Cherry Valley SM3 were fattened in-house on litter and fed commercial feeds (starter 1, starter 2, grower and finisher) according to the Cherry Valley Nutrition Manual for 45 days, up to a live weight of approximately 3 kg. The ducks were slaughtered and processed at an approved duck slaughterhouse. The slaughtering process included electrical water bath stunning, bleeding, scalding, plucking, waxing and additional plucking, evisceration, and chilling using an automated line with capacity for 4,000 ducks per hour. The average slaughterhouse capacity was approximately 325,000 of ducks per month. After being subjected to several partial washings during evisceration, the carcasses were air chilled (in presence of water mist) at 0-1°C to the final temperature of approx. 3°C, and finaly finished with washing of the whole carcass before chilling.
A total of 24 carcasses (graded as quality class A according to Regulation (EC) No. 543/2008) were purchased as fresh without offal, calibration 2,300 ± 50 g. The whole experiment was twice replicated within the year (n=72).
Samples preparation and storage
After purchasal, the carcasses were transported at a temperature up to 4°C and stored at 3°C ± 1°C till the next day, when they were packed for air storage (wrapped in polyolefin stretch film, n=36) or vacuum storage (pressure 3 mbar, using a packaging machine C250 from MULTIVAC, Germany, n=36). The foil used was Ergo.top-11mod/120µm/flatfilm, with a PA/EVOH/PE structure; permeability for O2: ≤ 2.0 cm3/m2 at a temperature of 23 ºC and 50% relative air humidity (Vepak, Czech Republic). The carcasses were stored at 3°C ± 1°C and subjected to analysis after 1, 3, 6 and 9 days of storage. At each sampling day, 3 carcasses per group were analysed (including the 2 replications, n = 9).
Microbiological analysis
Sampling took place according to EN ISO 6887-2. Samples were aseptically taken from the left half of each duck (both breast and thigh, both skin and deep muscle) and analysed for various groups of spoilage bacteria - Enterobacteriaceae, coliform bacteria and E. coli, Total Viable Count (TVC), psychrotrophic bacteria (PSY), Lactic Acid Bacteria (LAB); Pseudomonas spp. counts were determined in samples stored on air and Brochothrix thermosphacta in vacuum-packed samples. All the analyses were performed according to appropriate ISO norms, as previously described (Hulankova et al., 2018). In total, 288 samples were analysed.
Measurement of pH
The measurement of pH was performed as previously described (Hulankova et al., 2018).
Statistical analysis
The statistical analysis was performed using the open source statistical software R (R Development Core Team, 2020). An empty model was first run to check the influence of replication as the random effect. Since the effect was not significant (p>0.05), the factor of replication was not included into the final model. Briefly, a Linear Mixed Effects Model was used to evaluate the effect of the type of packaging (air or vacuum), location (breast or thigh), sample type (meat or skin) and the day of storage (1, 3, 6 or 9). The effect of individual effects and their interactions was evaluated using the lmerTest package (Kuznetsova et al., 2017) based on lme4 package (Bates et al., 2015). The function uses Satterthwaite approximation instead of Wald’s to derive P values, as this approximation was reported to produce acceptable Type 1 error rates (“false positive”), even for smaller datasets (Luke, 2017). Restricted maximum likelihood (REML) was used for estimation. The pairwise comparisons were evaluated using Tukey’s method of least square test from the emmeans package (Lenth, 2020). p<0.05 values were considered statistically significant.
RESULTS AND DISCUSSION
Fresh poultry, seafood and raw meat are considered high-risk and perishable foods. Raw poultry meat has a high content of nutrients and a high water activity. These factors create an ideal environment for rapid proliferation and/or long survival of many microorganisms, including both pathogenic and spoilage bacteria (Hakeem & Lu, 2021). Since duck meat is one of the minority groups in meat production and consumption statistics, the data on its microbiological quality are scarce in comparison to turkey, and especially chicken meats. Most factors assessed in this study were found to strongly influence the microbiological parameters (Table 1), and interactions were commonly found between the factors, meaning that the differences between levels of a given factor depended on the levels of other factors.
For Enterobacteriaceae and its subgroups, the main differences were noted between skin and meat samples, as could be expected. Whereas the skin samples showed initial values between 2 to 3 log CFU/g, the counts in meat samples were mostly below the detection limit till the 6th day of storage (Table 2). The counts of Enterobacteriaceae and coliforms were slightly higher in thigh samples than in breast samples, although the differences were mostly not significant. The counts increased significantly after 6 and 9 days of storage, when an accelerated growth in air was detected in comparison to vacuum-packed duck carcasses. The highest counts at the end of storage for Enterobacteriaceae were below 6 log CFU/g for skin samples in air, whereas the contamination of meat samples packed in vacuum were only 1.45 and 2.17 log CFU/g for breast and thigh, respectively. A study published by Lázaro et al. (2015) showed different results: thawed breast samples (100 g) of various species of poultry, including ducks were examined, being stored aerobically in plastic bags at 4 ± 1°C for 17 days. The initial values of Enterobacteriaceae group were under detection limit, but they gradually grew to 5.85 log CFU/g at day 9. In our study, such high concentrations of Enterobacteriaceae were detected only at the end of the storage period, and only in skin-containing samples.
E. coli was not detected in the meat throughout the whole storage period, and its counts on skin actually decreased toward the end of storage (p<0.01). Escherichia coli is often an indicator to assess enteric contamination (Li et al., 2019).
As TVC and PSY counts increased gradually during storage, the differences (as described previously for Enterobacteriaceae) between air and vacuum, meat and skin samples, and breast and thigh samples were more pronounced (Table 3). After 9 days of storage, the counts on skin in air increased during storage by up to 5 log CFU/g, reaching mean values of approximately 9 log CFU/g, whereas the counts in skin samples of vacuum-packed duck carcasses were lower (by 2 log CFU/g) and were comparable to meat from carcasses stored in air. The amount of TVC and PSY at the end of storage for both duck breast and duck leg samples was always 1-2 log orders of magnitude lower in the case of vacuum packing. The amount of microorganisms increased continuously for both types of samples, i.e. both skinless and skinned samples. Berrang et al. (2020) published a study concerning the microbiological status of duck carcasses during slaughter processing. The levels of TVC (2.9 ± 0.1 log CFU/ml), coliforms (0.6 ± 0.1 log CFU/ml) and E. coli (0.3 ± 0.1 log CFU/ml) were enumerated from carcass and leg quarter rinse. The TVC (log CFU/ml) was higher when compared to breast or thigh muscle samples including skin from our study on the first day of storage, but it is true that rinsing leads to more bacteria that can concentrate in feather follicles on the skin. In contrast, the E. coli and coliform counts in the study published by Berrang et al. (2020) are many times lower than the data obtained in our investigation. Lázaro et al. (2015) published initial values of approximately 3 log CFU/g for TVC in samples of duck breasts. These values gradually increased to 5.11 log CFU/g at day 9. The increase in the number of microorganisms observed was slower than in our study, although the storage temperature was slightly higher (4°C ± 1°C). Another study published by Li et al. (2019) on meat at retail reported a median TVC in chilled duck of 5.43 log CFU/g. In addition to TVC, they also monitored E. coli counts, which were 2.28 log CFU/g in chilled duck. Such high E.coli contamination was detected only on duck skin at the beginning of the chilled storage in our study.
The genus Pseudomonas includes more than 240 species, of which P. fluorescens, P. putida, P. fragi, P. lundensis, and P. weihenstephanensis are the most important in food spoilage. Pseudomonas spp. are the main spoilage bacteria in meat stored in air, but there are also studies confirming the growth of some representatives under anaerobic conditions (Papadopoulou et al., 2020; Kolbeck et al., 2021). There was a significant proliferation in our study, with counts on skin above 8 log CFU/g and above 9 log CFU/g after 6 and 9 d of storage, respectively. Pseudomonas spp. were thus the dominant microflora of duck carcasses stored in air (Table 4). The increase in numbers during storage was more pronounced in our study than in the model of Xing et al. (2023) for aerobically stored duck breast inoculated with Pseudomonas aeruginosa. In the Chinese study, the lag phase at 4°C was much longer (more than 6 d), and the counts increased by less than 1.5 log CFU/g after 9 d of storage. The difference can be explained by the varying growth potential at chilling temperatures among Pseudomonas strain, and by longer time available for adaptation of the bacteria in the naturally contaminated samples in comparison to the freshly inoculated ones.
Lactic acid bacteria (LAB) may act as protective cultures in foods due to their accelerated growth in anaerobic conditions and ability to produce antimicrobial metabolites, from simple organic acids to more complex compounds such as antimicrobial peptides. They have also been shown to limit the growth of spoilage bacteria, such as Clostridium spp. or pathogenic bacteria such as Listeria monocytogenes (Fidan et al., 2022). Lactic acid bacteria were generally low - the counts in meat samples were mostly below the detection limit till the 6th day of storage. In skin samples, the counts did not increase significantly during storage, and stayed below 3 log CFU/g with exception of thigh samples from vacuum-packed ducks, where the counts were slightly higher (Table 3). Increased concentration of carbon dioxide and vacuum packaging favours the growth of lactic acid bacteria, especially those of the genus Lactobacillus (Fidan et al., 2022). In general, vacuum-packed samples showed higher numbers than the samples left in air (p = 0.003).
Brochothrix thermosphacta is closely related to genuses Listeria and Lactobacillus. It can grow in atmospheres with a low oxygen level and/or high carbon dioxide concentration, and may thus cause spoilage in vacuum-packed or modified-atmosphere-packed meat. It can also proliferate at low temperatures (starting at 0°C). Growth and metabolic activities of B. thermosphacta during food storage result in the production of metabolites associated with off-odour (Illikoud et al., 2019; Patange et al., 2017). The results obtained in our experiment show that breast and thigh samples with skin represent a more suitable environment for the growth of B. thermosphacta than skinned meat samples. Although B. thermosphacta was not detected in meat during storage, the numbers on skin increased during storage in vacuum to up to 4.4 and 5 log CFU/g in breast and thigh, respectively, which proves that it has a greater spoilage potential than lactic acid bacteria in vacuum-packed duck meat (Table 4).
The initial higher microbial load in thigh samples in comparison to breast samples could be the result of higher contamination of this body part during evisceration (Althaus et al., 2017), but could also originate from higher pH values of thigh samples. The differences in pH result from white, glycolytic muscle fibres being predominant in breast muscles, which leads to higher level of acidification during meat ageing of poultry meat (Biswas et al. 2019). Unlike in chicken, the duck breast meat is darker, due to the presence of different types of muscle fibres at a different ratio. Smith et al. (1993) found 100% and 16% white fibres in breast muscle of chicken and duck, respectively. Similarly, in the study of Kim et al. (2008), chicken breast contained 100% of type IIB muscle fibres, while duck breast contained 73% type IIB and 27% type IIA muscle fibres; however, the differences in pH between duck and chicken breast 24 h post mortem were not statistically significant.
The pH of duck meat is in the range from 5.4 to 6.3 (Biswas et al., 2019). The pH is one of the most important intrinsic factors in meat that can influence microbial growth; on the other hand, pH can be influenced by metabolic products of spoilage microorganisms. The mean values of pH increased during storage and reached values above 7 in thigh skin stored for 9 d in air (Table 5). Skin from thighs stored in air also showed the highest numbers of PSY and Pseudomonas spp. which suggests an increased formation of alkaline compounds due to proteolysis. For the breast and thigh samples packed in vacuum, the variation was not as large as for the samples packed in air.
CONCLUSIONS
It can be concluded that the type of packaging and the presence of skin on the surface of the packaged duck meat influences the microbiological parameters studied. Samples of duck meat without skin packed in vacuum showed an overall more favourable microbiological result, and therefore vacuum can be recommended for extending the shelf life of duck meat.
ACKNOWLEDGMENTS
This study was funded by the Internal Creative Agency FVHE/Tremlová/ITA2019 of the University of Veterinary Sciences Brno.
REFERENCES
-
Althaus D, Zweifel C, Stephan R. Analysis of a poultry slaughter process:Influence of process stages on the microbiological contamination of broiler carcasses. Italian Journal of Food Safety 2017;6(4):190-4. https://doi.org/10.4081/ijfs.2017.7097
» https://doi.org/10.4081/ijfs.2017.7097 - AVEC - The Voice of Europeans Poultry Meat Sector. Annual Report 2022 . Brussels: Association of Poultry Processors and Poultry Trade in the EU Countries; 2022 [cited 2023 Jun 06]. Available from: https://avec-poultry.eu/resources/annual-reports/
-
Bates D, Maechler M, Bolker B, et al. Fitting linear mixed-effects models Using lme4. Journal of Statistical Software 2015;67(1):1-51. https://doi.org/10.18637/jss.v067.i01
» https://doi.org/10.18637/jss.v067.i01 -
Berrang ME, Meinersmann RJ, Knapp SW. Presence of bacterial pathogens and levels of indicator bacteria associated with duck carcasses in a commercial processing facility. Journal of Food Protection 2020;83(4):605-8. https://doi.org/10.4315/0362-028X.JFP-19-397
» https://doi.org/10.4315/0362-028X.JFP-19-397 -
Biswas S, Banerjee R, Bhattacharyya D, et al. Technological investigation into duck meat and its products - a potential alternative to chicken. World's Poultry Science Journal 2019;75(4):609-20. https://doi.org/10.1017/S004393391900062X
» https://doi.org/10.1017/S004393391900062X - Commission Regulation (EC) No 543/2008 of 16 June 2008 laying down detailed rules for the application of Council Regulation (EC) No 1234/2007 as regards the marketing standards for poultry meat. The Official Journal of the European Union 2008;157:46-87.
-
Fidan H, Esatbeyoglu T, Simat V, et al. Recent developments of lactic acid bacteria and their metabolites on foodborne pathogens and spoilage bacteria:Facts and gaps. Food Bioscience 2022;47:101741. https://doi.org/10.1016/j.fbio.2022.101741
» https://doi.org/10.1016/j.fbio.2022.101741 -
Hakeem MJ, Lu X. Survival and Control of Campylobacter in poultry production environment. Frontiers in Cellular and Infection Microbiology 2021;10:615049. https://doi.org/10.3389/fcimb.2020.615049
» https://doi.org/10.3389/fcimb.2020.615049 -
Hou W, Yue Q, Liu W, et al. Characterization of spoilage bacterial communities in chilled duck meat treated by kojic acid. Food Science and Human Wellness 2021;10:72-7. https://doi.org/10.1016/j.fshw.2020.05.015
» https://doi.org/10.1016/j.fshw.2020.05.015 -
Huda N, Putra A, Ahmad R. Potential application of duck meat for development of processed meat products. Current Research in Poultry Science 2011;1(1):1-11. https://doi.org/10.3923/crps.2010
» https://doi.org/10.3923/crps.2010 -
Hulankova R, Borilova G, Abdullah FAA, et al. Microbiological quality of organic chicken meat during refrigerated storage in air and modified atmospheres. British Poultry Science 2018;59(5):506-13. https://doi.org/10.1080/00071668.2018.1496399
» https://doi.org/10.1080/00071668.2018.1496399 -
Illikoud N, Rossero A, Chauvet R, et al. Genotypic and phenotypic characterization of the food spoilage bacterium Brochothrix thermosphacta. Food Microbiology 2019;81:22-31. https://doi.org/10.1016/j.fm.2018.01.015
» https://doi.org/10.1016/j.fm.2018.01.015 - Kim GD, Jeong JY, Moon SH, et al. Effects of muscle fiber type on meat characteristics of chicken and duck breast muscle. Proceedings of the 54th International Congress of Meat Science and Technology; 2008 Aug 10-15; Cape Town; 2008.
-
Kolbeck S, Abele M, Hilgarth M, et al. Comparative proteomics reveals the anaerobic lifestyle of meat-spoiling pseudomonas species. Frontiers in Microbiology 2021;12:664061. https://doi.org/10.3389/fmicb.2021.664061
» https://doi.org/10.3389/fmicb.2021.664061 -
Kuznetsova A, Brockhoff PB, Christensen RHB. lmerTest package: tests in linear mixed effects models. Journal of Statistical Software 2017;82(13):1-26. https://doi.org/10.18637/jss.v082.i13
» https://doi.org/10.18637/jss.v082.i13 -
Lázaro CA, Conte-Júnior CA, Canto AC, et al. Biogenic amines as bacterial quality indicators in different poultry meat species. LWT - Food Science and Technology 2015;60(1):15-21. https://doi.org/10.1016/j.lwt.2014.09.025
» https://doi.org/10.1016/j.lwt.2014.09.025 -
Lenth RV. Emmeans: Estimated Marginal Means aka least-squares means. R package version 1.5.3 2020. Available from: https://CRAN.R-project.org/package=emmeans
» https://CRAN.R-project.org/package=emmeans -
Li Y, Pei X, Zhang X, et al. A surveillance of microbiological contamination on raw poultry meat at retail markets in China. Food Control 2019;104:99-104. https://doi.org/10.1016/j.foodcont.2019.04.037
» https://doi.org/10.1016/j.foodcont.2019.04.037 -
Luke SG. Evaluating significance in linear mixed-effects models in R. Behavior Research Methods 2017;49(4):1494-502. https://doi.org/10.3758/s13428-016-0809-y
» https://doi.org/10.3758/s13428-016-0809-y -
Mangalassary S. Advances in packaging of poultry meat products. In: Venkitanarayanan K, Thakur S, Ricke SC. Food safety in poultry meat production. Cham: Springer Nature; 2019. p.139-59. https://doi.org/10.1007/978-3-030-05011-5
» https://doi.org/10.1007/978-3-030-05011-5 -
Nauman K, Jaspal MH, Asghar B, et al. Effect of different packaging atmosphere on microbiological shelf life physicochemical attributes and sensory characteristics of chilled poultry fillets. Food Science of Animal Resources 2022;42(1):153-74. https://doi.org/10.5851/kosfa.2021.e71
» https://doi.org/10.5851/kosfa.2021.e71 -
Papadopoulou OS, Iliopoulos V, Mallouchos A, et al. Spoilage potential of pseudomonas (P. fragi P. putida) and LAB (Leuconostoc mesenteroides Lactobacillus sakei) strains and their volatilome profile during storage of sterile pork meat using GC/MS and data analytics. Foods 2020;9:633. https://doi.org/10.3390/foods9050633
» https://doi.org/10.3390/foods9050633 -
Patange A, Boehm D, Bueno-Ferrer C, et al. Controlling Brochothrix thermosphacta as a spoilage risk using inpackage atmospheric cold plasma. Food Microbiology 2017;66:48-54. https://doi.org/10.1016/j.fm.2017.04.002
» https://doi.org/10.1016/j.fm.2017.04.002 - R Core Team. R: a language and environment for statistical computing. Vienna: R Foundation for Statistical Computing; 2020. Available from: https://www.R-project.org/
-
Smith DP, Fletcher DL, Buhr RJ, et al. Pekin ducklings and broiler chicken pectoralis muscle structure and composition. Poultry Science 1993;72(1):202-8. https://doi.org/10.3382/ps.0720202
» https://doi.org/10.3382/ps.0720202 -
Vorotnikov V. Duck meat production is booming in Poland. 2022 [cited 2023 Jun 01]. Available from: https://www.poultryworld.net/poultry/other-species/duck-meat-production-is-booming-in-poland/
» https://www.poultryworld.net/poultry/other-species/duck-meat-production-is-booming-in-poland -
Xing S, Liu K, Gong H, et al. Predictive model for growth of Pseudomonas spp. on fresh duck breast as a function of temperature. Poultry Science 2023;102(9):102868. https://doi.org/10.1016/j.psj.2023.102868
» https://doi.org/10.1016/j.psj.2023.102868 -
Zouharova A, Bartakova K, Bursova S, et al. Meat and fish packaging and its impact on the shelf life - a review. Acta Veterinaria Brno 2023;92:95-108. https://doi.org/10.2754/avb202392010095
» https://doi.org/10.2754/avb202392010095
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Funding
Internal Creative Agency FVHE/Tremlová/ITA2019, University of Veterinary Sciences Brno.
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Data availability statement
Data are available upon request.
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Disclaimer/Publisher’s Note
The published papers’ statements; opinions; and data are those of the individual author(s) and contributor(s). The editor(s) disclaim responsibility for any injury to people or property resulting from any ideas; methods; instructions; or products referred to in the content.
Data are available upon request.
