Pre-harvest application of calcium chloride and chitosan on fruit quality and storability of ‘Early Swelling’ peach during cold storage

Efeito da aplicação pré-colheita de cloreto de cálcio e quitosano na qualidade e no armazenamento de frutos de pessegueiro da variedade ‘Early Swelling’ durante o armazenamento a frio

Ahmed Abdel Nabi Abdel Gayed Samar Abdeltawab Mohamed Ahmed Shaarawi Mohamed Abdelkader Elkhishen Nabil Raafat Mohamed Elsherbini About the authors

ABSTRACT

Studies related with the storage of peach fruits have received great relevance in Egypt. In this study, the effect of pre-harvest sprays of calcium chloride and chitosan, separately and in combination, on quality attributes and storability of peach fruits stored at 0±1 °C was studied. ‘Early Swelling’ peach trees were sprayed twice with 1% or 2% calcium chloride. The first spraying was at pea stage, while the second one was performed at 10 days before harvesting. Chitosan sprays were performed at 0.5 or 1%, alone or in combination with 1 and 2% calcium chloride, at 10 days before harvesting. Untreated trees served as control. Fruits were harvested at maturity stage, then packaged and stored at 0±1 °C and 85-90% of relative humidity. Fruit physical and chemical properties were evaluated at 7-day intervals. Results showed that pre-harvest application with 2% CaCl2+1% chitosan was most effective in minimizing weight loss (%) and decay (%), as well as in maintaining maximum firmness and lengthening shelf life. Fruit color was not affected by any of the treatments, while untreated fruits and calcium chloride treatment alone, at both applied concentrations, maintained higher total soluble solids (TSS, %), total phenolic content, and lower titratable acidity percentage.

Index terms:
Alternative chemicals; CaCl2; quality attributes.

RESUMO

Estudos relacionados ao armazenamento de pêssego tem sido considerado de grande relevância no Egito. Neste estudo, o efeito da pulverização pré-colheita com cloereto de calico e quitosano, isoladamente ou em conjunto, na qualidade e na capacidade de armazenamento de frutos de pessegueiro armazenados a 0±1 °C foi avaliada. Frutos da variedade ‘Early Swelling’ foram tratados com 1,0 ou 2,0% de cloreto de cálcio. O primeiro tratamento foi aplicado num estado precoce de formação do fruto enquanto o segundo foi aplicado 10 dias antes da colheita. Quitosano foi aplicado nas concentrações de 0,5 ou 1,0%, isoladamente ou em combinação com 1,0% ou 2,0% de cloreto de cálcio também 10 dias antes da colheita. Árvores não tratadas serviram como controle. Os frutos foram colhidos quando maduros, empacotados e mantidos a 0±1 °C e sob condições de humidade relativa de 85-90%. Propriedades físicas e químicas dos frutos foram avaliadas em intervalos de 7 dias. Os resultados mostraram que a aplicação de 2% CaCl2 + 1% quitosano foi a mais eficaz em minimizar a perda de peso (%) e a senescência (%), bem como na manutenção da rigidez e aumento do período de vida em prateleira. A cor dos frutos não foi afectada por nenhum dos tratamentos enquanto frutos não tratados e cloreto de cálcio isoladamente, em ambas as concentrações, mantiveram um elevado teor de sólidos solúveis totais (TSS, %), elevado teor de fenóis e reduzida percentagem de acidez de titulação.

Termos para indexação:
Químicos alternativos; CaCl2; atributos qualitativos.

INTRODUCTION

Peach (Prunus persica (L.) Batsch) belongs to the family Rosaceae and is one of the most popular fruits in the world because of its high nutrient value and pleasant flavor. Peach is considered as one of the most important deciduous fruits in Egypt, where it has great success and is widespread in the newly reclaimed areas. The storage of peach fruits is problematic due to a short post-harvest life, as fruits quickly pass from ideal maturity to over ripening phase, readily lose water and shrivel, can be attacked and destroyed by fruit rotting organisms and become unmarketable as a result of the internal breakdown. An increased concern among consumers about food safety and the potentially harmful health effects of chemical residues encouraged research to find safe alternative chemicals which can maintain the marketable quality throughout prolonged storage period of fruits, including peach.

In this sense, pre- and post-harvest application of calcium may delay senescence in fruits with no detrimental effect on consumer acceptance. Calcium is a key plant nutrient that has a significant role in cell functions, including reducing softening and senescence of fruits (Barker; Pilbeam, 2015BARKER, A. V.; PILBEAM, D. J. Handbook of Plant Nutrition. 2.ed. Taylor & Francis Group, Boca Raton, Florida, 2015. 773p.), and it is also considered the most important mineral element determining fruit quality (El-Badawy, 2012EL-BADAWY, H. E. M. Effect of chitosan and calcium chloride spraying on fruits quality of Florida Prince peach under cold storage. Research Journal of Agriculture and Biological Sciences, 8(2): 272-281, 2012.). The role of calcium in stabilizing cellular membranes and delaying senescence in horticultural crops, (Poovaiah; Glenn; Reddy, 1988POOVAIAH, B. W.; GLENN, G. M.; REDDY, A. S. N. Calcium and fruit softening: Physiology and biochemistry. Horticultural Reviews, 10:107-152, 1988.), as well as its contribution to the linkages between pectic substances within the cell-wall are well known. Pre-harvest calcium treatments to increase calcium content of the cell wall were effective in delaying senescence, resulting in firmer and higher fruit quality (Serrano et al., 2004SERRANO, M. et al. Effect of preharvest sprays containing calcium, magnesium and titanium on the quality of peaches and nectarines at harvest and during postharvest storage. Journal of the Science of Food and Agriculture , 84(11):1270-1276, 2004.). The mobility of calcium in trees is low, and the root uptake from fertilized soils is poorly effective in increasing the calcium content in fruits. In this context, Ghani, Awang and Sijam (2011GHANI, M. A. A.; AWANG, Y.; SIJAM, K. Disease occurrence and fruit quality of pre-harvest calcium treated red flesh dragon fruit (Hylocereusm polyrhizus). African Journal of Biotechnology, 10(9):1550-1558, 2011), reported that the direct application of liquid source of calcium on leaves and fruits may offer an alternative solution. Calcium may have also a potential use as an alternative method in integrated disease management (Biggs; Hogmire; Collins, 2000BIGGS, A. R.; HOGMIRE, H. W.; COLLINS, A. R. Assessment of an alternative IPM program for the production of apples for processing. Plant Disease Journal, 84:1140-1146, 2000.).

Chitosan is an N-acetylated derivative of the polysaccharide chitin. It is a natural polymer with a polycationic nature, which has numerous applications in agriculture (e.g., as soil modifier, films, fungicide, elicitor) and agroindustry, as well as in cosmetics, biomedicine, environmental protection, wastewater management (Deepmala et al., 2014DEEPMALA, K. et al. A future perspective in crop protection: Chitosan and its oligosaccharides. Advances in Plants & Agriculture Research, 1(1):00006, 2014.). Chitosan is edible and safe for humans (Rhoades; Roller, 2000RHOADES, J.; ROLLER, S. Antimicrobial actions of degraded and native chitosan against spoilage organisms in laboratory media and foods. Applied and Environmental Microbiology, 66(1):80-86, 2000.), and it is used in human medicine, advised in slimming diets (Maezaki et al., 1993MAEZAKI, Y. et al. Hypocholesterolemic effect of chitosan in adult males. Bioscience, Biotechnology and Biochemistry, 57(9):1439-1444, 1993.). Due to these properties, chitosan could be applied near harvest time. Many studies have shown the high potential of chitosan for preserving fresh fruits and vegetables. Pre-harvest spraying with chitosan is highly feasible and has a beneficial effect on fruit quality attributes (Reddy et al., 2000REDDY, B. M. V. et al. Effect of pre-harvest chitosan sprays on post-harvest infection by Botrytis cinereal and quality of strawberry fruit. Postharvest Biology and Technology , 20:39-51, 2000.). Chitosan has been also considered as a valid alternative to synthetic fungicides (El Ghaouth, 1997EL GHAOUTH, A. Biologically-based alternatives to synthetic fungicides for the control of postharvest diseases. Jornal of Industrial Microbiology and Biotechnology, 19:160-162, 1997.). Romanazzi (2010ROMANAZZI, G. Chitosan treatment for the control of postharvest decay of table grapes, strawberries and sweet cherries. Global Science Books, Fresh Produce 4 (Special Issue 1):111-115, 2010.) reported that chitosan has a double mechanism of actions, i.e., it inhibits the development of decay-causing fungi, and induces resistance responses of host tissues. It is considered as an ideal preservative coating because it has a disease suppressive effect, resulting from both physical and biochemical mechanisms. The physical properties of the polymer allow it to produce a film on the surface of treated fruit (Du; Gemma; Iwahori, 1998DU, J.; GEMMA, H.; IWAHORI, S. Effects of chitosan coating on the storability and on the ultra-structural changes of ‘Jonagold’ apple fruit in storage. Food Preservation Sciences, 24:23-29, 1998.), and has also the potential to prolong the storage life of many fruits, such as peach, Japanese pear, kiwifruit, strawberry and sweet cherry (Du; Gemma; Iwahori, 1997DU, J.; GEMMA, H.; IWAHORI, S. Effects of chitosan coating on the storage of peach, Japanese pear and kiwifruit. Journal of the Japanese Society for Horticultural Science, 66(1):15-22, 1997. ; EL Ghaouth; Ponnampalam; Boulet, 1991EL GHAOUTH, A.; PONNAMPALAM, R.; BOULET, M. Chitosan coating effect on storability and quality of fresh strawberries. Journal of Food Science, 56:1618-1621, 1991.; Romanazzi; Nigro; Ippolito, 2003ROMANAZZI, G.; NIGRO, F.; IPPOLITO, A. Short hypobaric treatments potentiate the effect of chitosan in reducing storage decay of sweet cherries. Postharvest Biology and Technology , 29(1):73-80, 2003.). Chitosan also induces chitinase activity, and elicits phytoalexins and defense barriers in the host tissues (El Ghaouth et al.,1992EL GHAOUTH, A. et al. Antifungal activity of chitosan on two postharvest pathogens of strawberry fruits. Phytopathology, 82:398-402, 1992.), as well as the defense responses in several plant systems.

Calcium has a general application in either pre-harvest or post-harvest treatments, while reports on pre-harvest application of chitosan are limited (El-Badawy, 2012EL-BADAWY, H. E. M. Effect of chitosan and calcium chloride spraying on fruits quality of Florida Prince peach under cold storage. Research Journal of Agriculture and Biological Sciences, 8(2): 272-281, 2012.; Reddy et al., 2000REDDY, B. M. V. et al. Effect of pre-harvest chitosan sprays on post-harvest infection by Botrytis cinereal and quality of strawberry fruit. Postharvest Biology and Technology , 20:39-51, 2000.). In this study, the effect of pre-harvest application of calcium chloride, chitosan and their combination on storability and quality attributes of peach fruits, cv Early Swelling, has been investigated.

MATERIAL AND METHODS

The present study was conducted through two successive seasons (2014 and 2015) on peach (Prunus persica), cv Early Swelling. Trees were grown in a private orchard at El- Khatatba City, in El-Menufiya Governorate, Egypt, in a sandy soil. Trees were 7 years old, budded on ‘Nemaguard’ peach rootstock, cultivated at 4×4 m distance, open-vase shape trained, drip irrigated, and received normal cultural practices adopted in the orchard.

Experimental design

Each treatment consisted of three trees in a randomized complete block design where a single tree represented the experimental unit. The experiment consisted of a total of nine treatments (including the control) for each season. The treatments were: (i) 1 or 2% calcium chloride, with two sprayings of trees, the 1st at “pea stage”, the 2nd 10 days before harvesting, (ii) 0.5 or 1% chitosan, alone or in combination with 1 or 2% calcium chloride, with only one spraying, 10 days before harvesting. A set of trees were left untreated and served as control. Trees were sprayed with hand-sprayer, till fruits were completely wet to run off. Samples of fruits at full maturation from each treatment were hand-harvested during the first two weeks of May. In the laboratory of the Faculty of Agriculture, Cairo University, fruits of each treatment were then sorted and selected for uniformity of weight, size, and absence of mechanical damage or visible pathological infections. The selected fruits were packed in carton boxes (2 kg capacity). Each treatment was triplicated. Fruits were then stored for 35 days at 0±1 °C with a relative humidity (RH) of 85-90%. Fruit physical and chemical quality attributes were periodically assessed at intervals of 7 days throughout all the storage period.

Quality assessments of fruits by physical characteristics

The following physical characteristics were evaluated:

Weight loss: Samples of each treatment were weighed at weekly intervals until the end of experiment. Weight loss (%) was calculated as follows:

Fruit weight loss (%) = [(initial weight - weight at sampling date / initial weight)] x 100.

Fruit decay percentage: evaluated by type, as skin appearance, shriveling, chilling injury and pathogenic rots. In every inspection date, decayed fruits were discarded and the relative amount expressed as decay percentage.

Fruit firmness (kg/cm2): fruits from each replicate were taken at weekly intervals to determine the changes in fruit firmness using stationary firmness tester. Fruit firmness was measured in two opposite sides of the equatorial fruit zone after removing the peel, and expressed in kg/cm2.

Shelf life (days): after 35 days of cold storage, fruit samples of each treatment were placed at ambient temperature, and shelf life was determined as a number of days of which fruits maintained acceptable eating quality and appearance.

Color assessment: hue angle (ho) values of fruits were assessed using a Minolta colorimeter CR-40 (Konica Minolta Sensing Inc, Sakai, Japan).

Quality assessments of fruits by chemical characteristics

The following chemical characteristics were evaluated:

Fruit total soluble solids: total soluble solids (TSS) were measured using digital pocket refractometer (model PAL 1, ATAGOTM, Tokyo Tech.) and expressed as percentage.

Fruit titratable acidity: titratable acidity (TA) was measured in the juice of fruit sample for each replicate by titration against calibrated 0.1N NaOH solution in the presence of phenolphthalein as an indicator. Acidity was calculated as percentage of malic acid according to A.O.A.C. (https://archive.org/details/gov.law.aoac.methods.1.1990).

Total phenols: total phenolics were analyzed spectrophotometrically using the method described by Swain and Hillis (1959SWAIN, T.; HILLIS, W. E. The phenolic constituents of Prunus domestica. I. The quantitative analysis of phenolic constituents. Journal of the Science of Food and Agriculture , 10(1):63-68, 1959.). Results were expressed as g of gallic acid /100 g fresh weight (FW).

Statistical analysis

The experiment was conducted using a completely randomized design with three replicates. Data from the analytical determinations were subjected to analysis of variance (ANOVA). Mean comparisons were performed by Duncan’s Multiple range test at 5% level (Snedecor; Cochran, 1982SNEDECOR, G. W.; COCHRAN, W. G. Statistical Methods. 7th Ed. The Iowa State University. Press, Ames Iowa, USA, 1982. 292p.).

RESULTS AND DISCUSSION

Weight loss (%)

The percentage of weight loss increased all through the storage period (Table 1). With regard to the effect of the tested pre-harvest treatments, considering mean values at the end of the analyzed period of time, in both seasons the highest significant weight loss percentage was obtained by untreated fruits (control), while treatments with chitosan and CaCl2 (at different concentrations, depending on the season) recorded the lowest significant weight loss. Other treatments did not show clear differences among them, especially in the first season, although mean values resulted always significantly higher than the control fruits. The lowest fruit weight loss (%) was obtained in fruits treated with 1% CaCl2 + 1% chitosan after 7 days of storage.

Table 1:
Effect of some pre-harvest treatments on weight loss (%) of ‘Early Swelling’ peach fruits stored at 0±1 ºC during 2014 and 2015 seasons. Different letters indicate significantly different values by ANOVA followed by Duncan test at P≤0.05 (small letters refer to values recorded in each season, capital letters refer to mean values).

Weight loss of fresh fruits is mainly due to water loss as a result of evaporation and transpiration, while the amount of dry matter is lost by respiration. Results of this study on weight loss reduction are in accordance with what observed on ‘Florida prince’ peach (El-Badawy, 2012EL-BADAWY, H. E. M. Effect of chitosan and calcium chloride spraying on fruits quality of Florida Prince peach under cold storage. Research Journal of Agriculture and Biological Sciences, 8(2): 272-281, 2012.) and plums (Kirmani et al., 2013KIRMANI, S. N. et al. Effect of preharvest application of calcium chloride (CaCl2), gibberlic acid (GA3) and napthelenic acetic acid (NAA) on storage of plum (Prunus salicina L.), cv. Santa Rosa, under ambient storage conditions. African Journal of Agricultural Research, 8(9):812-818, 2013.), where a progressive and significant increase in physiological loss in weight (PLW) of fruits with the increase in storage duration was recorded. However, the increase in PLW of calcium chloride-treated fruits was relatively slower and, consequently, these fruits exhibited significantly lower overall losses as compared to other treatments and control fruits. The reduction in weight loss in CaCl2 treated fruits might be due to the maintenance of fruit firmness and tissue rigidity by decreasing the enzyme activity responsible for disintegration of cellular structure, which decreases the gaseous exchange (Levy; Poovaiah, 1979LEVY, D.; POOVAIAH, B. W. Effect of calcium infiltration of senescence of apples. Horticulture Science, 14:466, 1979.).

In this study, chitosan proved to be an effective coating reducing weight loss, alone as reported on longan fruit (Jiang; Li, 2001JIANG, Y.; LI, Y. Effects of chitosan coating on postharvest life and quality of longan fruit. Food Chemistry , 73(2):139-143, 2001. ), or in combination with calcium chloride on peach (El-Badawy, 2012EL-BADAWY, H. E. M. Effect of chitosan and calcium chloride spraying on fruits quality of Florida Prince peach under cold storage. Research Journal of Agriculture and Biological Sciences, 8(2): 272-281, 2012.). Chitosan coatings act as barriers, thereby restricting water transfer and protecting fruit skin from mechanical injuries, as well as sealing small wounds and thus delaying dehydration (Ribeiro et al., 2007RIBEIRO, C. et al. Optimization of edible coating composition to retard strawberry fruit senescence. Postharvest Biology and Technology , 44:63-70, 2007.).

Decay (%)

In both seasons, decay percentages had progressive increment as the storage period increased (Table 2). Decay incidence started at the second week of storage, and gradually increased up to day 35 of storage. Pre-harvest treatments of 2% CaCl2+1% chitosan, 1% CaCl2+1% chitosan, and 2% CaCl2+0.5 % chitosan, in this order, recorded the lowest significant decay percentages. On the whole, the lowest fruit decay (%) was obtained when the fruits were treated with 2% CaCl2+1% chitosan and stored for 14 days; on the contrary, the highest significant decay percentage was gained following 35 days of storage period of untreated fruits (control).

Table 2:
Effect of some pre-harvest treatments on decay (%) of ‘Early Swelling’ peach fruits stored at 0±1 ºC during 2014 and 2015 seasons. Different letters indicate significantly different values by ANOVA followed by Duncan test at P≤0.05 (small letters refer to values recorded in each season, capital letters refer to mean values).

Results here may be attributed to the role of calcium ions in reducing fruit softening by strengthening the cell walls, as well as of chitosan covering cuticle and lenticels. Moreover, their high antifungal activity reduces respiration, ripening processes and infection during storage. Results of this study are in agreement with previous reports which indicated that calcium chloride spray reduces physiological disorders of fruits and increases their resistance to infection than untreated ones (Kirmani et al., 2013KIRMANI, S. N. et al. Effect of preharvest application of calcium chloride (CaCl2), gibberlic acid (GA3) and napthelenic acetic acid (NAA) on storage of plum (Prunus salicina L.), cv. Santa Rosa, under ambient storage conditions. African Journal of Agricultural Research, 8(9):812-818, 2013.).

Chitosan modifies gas exchange of fruit with the atmosphere, and its internal gas composition by producing a film coating on the surface. The suppressive effect on decay by chitosan can be in part attributed to delaying the senescence process. Chitosan, as a natural polycation compound, c limit fungal decay of fruits by its direct antifungal activity (Bautista-Banos et al., 2006BAUTISTA-BANOS, S. et al. Chitosan as a potential natural compound to control pre- and postharvest diseases of horticultural commodities. Crop Protection, 25:108-118, 2006.), induction of host resistance to pathogens (Trotel-Aziz et al., 2006TROTEL-AZIZ, P. et al. Chitosan stimulates defense reactions in grapevine leaves and inhibits development of Botrytis cinerea. European Journal of Plant Pathology, 114:405-413, 2006.), and its self-polymerisation that covers the fruit surface (Gonzalez-Aguilar, 2009GONZALEZ-AGUILAR, G. A. et al. Effect of chitosan coating in preventing deterioration and preserving the quality of fresh-cut papaya. Journal of the Science of Food and Agriculture, 89:15-23, 2009.). It offers a protection against deterioration by slowing decay and ripening; moreover, its protective effect is very high against infection (Reddy et al., 2000REDDY, B. M. V. et al. Effect of pre-harvest chitosan sprays on post-harvest infection by Botrytis cinereal and quality of strawberry fruit. Postharvest Biology and Technology , 20:39-51, 2000.). For all these properties, chitosan has a potential to prolong storage life and control decay of fruits. As for the combination of chitosan and calcium chloride, its potential as fungal decay inhibitors has been reported also by Muñoz et al. (2008MUÑOZ, P. H. et al. Effect of chitosan coating combined with postharvest calcium treatment on strawberry (Fragara ananassa) quality during refrigerated storage. Food Chemistry , 110(2):428-435, 2008.).

The results of pre-harvest chitosan efficiency in reducing decay percentages are in accordance with those obtained by Reddy et al. (2000REDDY, B. M. V. et al. Effect of pre-harvest chitosan sprays on post-harvest infection by Botrytis cinereal and quality of strawberry fruit. Postharvest Biology and Technology , 20:39-51, 2000.) that evidenced the protection effect against infection due to pre-harvest chitosan spray of Botrytis cinerea. Similar findings have been also reported on grape (Meng et al., 2008MENG, W. et al. Physiological responses and quality attributes of table grape fruit to chitosan preharvest spray and postharvest coating during storage. Food Chemistry , 106:501-508, 2008.), citrus (Chien; Sheu; Yang, 2007CHIEN, P. J.; SHEU, F.; YANG, F. H. Effects of edible chitosan coating on quality and shelf-life of sliced mango fruit. Journal of Food Engineering, 78(1):225-229, 2007.), ‘Florida prince’ peach (El-Badawy, 2012EL-BADAWY, H. E. M. Effect of chitosan and calcium chloride spraying on fruits quality of Florida Prince peach under cold storage. Research Journal of Agriculture and Biological Sciences, 8(2): 272-281, 2012.).

Fruit firmness (kg/cm2)

Fruit firmness is one of the most crucial factors in determining the post-harvest quality and physiology of fruits (Kirmani et al., 2013KIRMANI, S. N. et al. Effect of preharvest application of calcium chloride (CaCl2), gibberlic acid (GA3) and napthelenic acetic acid (NAA) on storage of plum (Prunus salicina L.), cv. Santa Rosa, under ambient storage conditions. African Journal of Agricultural Research, 8(9):812-818, 2013.). Data presented in Table 3 show that fruit firmness has significantly decreased as the storage period increased, reaching its lowest values at the end of storage period, regardless of the pre-harvest treatments. All treatments recorded significantly high firmness than control fruits; however, in both seasons, 2% CaCal2+1% chitosan showed, at each period, with few exceptions, the highest values of peach firmness. It should be noted that all the treatments had an effect in preserving fruit firmness as, at the end of the storage period, the lowest firmness value was obtained by the untreated fruits.

Table 3:
Effect of some pre-harvest treatments on firmness (kg/cm2) of ‘Early Swelling’ peach fruits stored at 0±1 ºC during 2014 and 2015 seasons. Different letters indicate significantly different values by ANOVA followed by Duncan test at P≤0.05 (small letters refer to values recorded in each season, capital letters refer to mean values).

Fruit softening is caused either by breakdown of insoluble proto-pectins into soluble pectin or by hydrolysis of starch (Matto et al., 1975MATTO, A. K. et al. Chemical changes during ripening and senescence. In: PANTASTICO, E. B. Postharvest physiology, handling and utilisation of subtropical fruits and vegetables. AVI Publishing Co. Inc. Westport, Connecticut, 1975. p.103-127.), or by increased membrane permeability caused by cellular disintegration (Oogaki; Wang; Gemma, 1990OOGAKI, C.; WANG, H. G.; GEMMA, H. Physiological and biochemical characteristics and keeping qualities of temperate fruits during chilled storage. Acta Horticulturae, 279:541-558, 1990.). The loss of pectic substances in the middle lamellae of the cell wall is perhaps the key step in ripening process that leads to the loss of cell integrity or firmness (Solomes; Latics, 1973SOLOMES, T.; LATICS, G. G. Cellular organisation and fruit ripening. Nature, 245:390-392, 1973.). The desired effect of calcium in maintaining fruit firmness may be due to the calcium binding to free carboxyl groups of polygalacturonate polymer, stabilizing and strengthening the cell wall, which in turn may strengthen the tissue thus becoming more resistant to hydrolytic enzyme activity, where calcium inhibits the polygalacturonase activity in cell walls (Buescher; Hobson, 1982BUESCHER, R. W.; HOBSON, G. E. Role of calcium and chelating agents in regulating the degradation of tomato fruit tissue by polygalacharonase. Journal of Food Biochemistry, 6:78-84, 1982.). Results here regarding the role of CaCl2 in the reduction of fruit softening are in correlation with those obtained on plums (Kirmani et al., 2013KIRMANI, S. N. et al. Effect of preharvest application of calcium chloride (CaCl2), gibberlic acid (GA3) and napthelenic acetic acid (NAA) on storage of plum (Prunus salicina L.), cv. Santa Rosa, under ambient storage conditions. African Journal of Agricultural Research, 8(9):812-818, 2013.) and strawberry (Muñoz et al., 2008MUÑOZ, P. H. et al. Effect of chitosan coating combined with postharvest calcium treatment on strawberry (Fragara ananassa) quality during refrigerated storage. Food Chemistry , 110(2):428-435, 2008.). All these reports evidenced a similar reduction in the firmness loss following the pre-harvest application of CaCl2.

Pre-harvest beneficial effect of chitosan on fruit firmness could be due to the formation of a chitosan film on fruit which can act as a barrier for O2 uptake, thereby slowing the metabolic activity, and consequently the ripening process (Reddy et al., 2000REDDY, B. M. V. et al. Effect of pre-harvest chitosan sprays on post-harvest infection by Botrytis cinereal and quality of strawberry fruit. Postharvest Biology and Technology , 20:39-51, 2000.). Higher firmness during the storage period of ‘Early swelling’ peach fruits following pre-harvest chitosan treatments are in harmony with those observed in previous studies on peach fruits (Brar; Simnani; Kaundal, 1997BRAR, S. S.; SIMNANI, S. S. A.; KAUNDAL, G. S. Effect of pre-harvest sprays of calcium nitrate on the storage life of Shan-I-Punjab peach. Journal of Research, 34(2):174-180, 1997.; Li; Yu, 2000LI, H.; YU, T. Effect of chitosan on incidence of brown rot, quality and physiological attributes of postharvest peach fruit. Journal of the Science of Food and Agriculture , 81:269-274, 2000.), as they reported that chitosan treatments delayed the loss of firmness. In addition, Reddy et al. (2000)REDDY, B. M. V. et al. Effect of pre-harvest chitosan sprays on post-harvest infection by Botrytis cinereal and quality of strawberry fruit. Postharvest Biology and Technology , 20:39-51, 2000. reported the beneficial effect of pre-harvest chitosan sprays on flesh firmness of strawberries; moreover, they found that fruit firmness correlated with the increasing of chitosan concentration.

Hue angle (ho)

Hue angle (ho) values showed a significant decline along the storage periods, irrespective of the applied treatments (Table 4). Indeed, all the treatments exerted a gradual decrease of h° along the storage periods, with the highest mean value in the first season (2014) recorded by 0.5% chitosan. In the second season (2015), no significant differences between treatments were recorded. At the end of the storage period (35 days), highest ho values were shown with fruits treated with 0.5 and 1% chitosan, in the first and second season, respectively. Muñoz et al. (2008MUÑOZ, P. H. et al. Effect of chitosan coating combined with postharvest calcium treatment on strawberry (Fragara ananassa) quality during refrigerated storage. Food Chemistry , 110(2):428-435, 2008.) reported that the h° of un-treated strawberry fruits began to decrease after the second day of storage and, at the end of the storage period (7 days) the decline was 32%. Moreover, calcium and chitosan treated fruits failed to show significant change during the storage period. They suggested that the control of moisture loss by chitosan coating contributes to minimizing external color changes in fully ripe strawberries. Wang et al. (2007WANG, J. et al. Quality and shelf life of mango (Mangifera indica L., cv. Tainong) coated by using chitosanand polyphenols. Food Science and Technology International, 13(4):317-322, 2007.) reported that post-harvest treatments with ‘Chito-care’ significantly reduced the color change rate of mango fruits during their storage, compared to untreated fruits.

Table 4:
Effect of some pre-harvest treatments on hue angle (ho) of ‘Early Swelling’ peach fruits stored at 0±1 ºC during 2014 and 2015 seasons. Different letters indicate significantly different values by ANOVA followed by Duncan test at P≤0.05 (small letters refer to values recorded in each season, capital letters refer to mean values).

Shelf life (days)

The application of chitosan or CaCl2 at different concentrations had a high effect on post-harvest shelf-life of ‘Early swelling’ peach fruits (Table 5). In both seasons, maximum effect was achieved by the treatment with 2% CaCl2+1% chitosan, and the recorded value (4.33) was significantly greater than all other treatments in the second season (2015).

Table 5:
Effect of some pre-harvest treatments on shelf life (days) of ‘Early Swelling’ peach fruits after 35 days of cold storage at 0±1 ºC during 2014 and 2015 seasons. Different letters indicate significantly different values by ANOVA followed by Duncan test at P≤0.05.

Calcium chloride has been extensively used for improving fruit quality, delaying deterioration in storage and thereby increasing the shelf life of various fruits (Kirmani et al., 2013KIRMANI, S. N. et al. Effect of preharvest application of calcium chloride (CaCl2), gibberlic acid (GA3) and napthelenic acetic acid (NAA) on storage of plum (Prunus salicina L.), cv. Santa Rosa, under ambient storage conditions. African Journal of Agricultural Research, 8(9):812-818, 2013.). For instance, El-Badawy (2012), Mahajan and Sharma (2000MAHAJAN, B. C.; SHARMA, R. C. Effect of pre-harvest application of growth regulators and calcium chloride on chemical characteristic and storage life of peach, cv. Shane e Punjab Haryana. Journal of Horticultural Sciences, 29(1-2):41-43, 2000.) on peaches, and Kirmani et al. (2013)KIRMANI, S. N. et al. Effect of preharvest application of calcium chloride (CaCl2), gibberlic acid (GA3) and napthelenic acetic acid (NAA) on storage of plum (Prunus salicina L.), cv. Santa Rosa, under ambient storage conditions. African Journal of Agricultural Research, 8(9):812-818, 2013. on plums, reported that shelf life was longer in pre-harvest Ca-treated fruits. Calcium treatment has been shown to decrease respiration, reduce ethylene production and slow down the onset of ripening in apple (Ferguson, 1984FERGUSON, I. B. Calcium in plant senescence and fruit ripening. Plant Cell Environment, 7(6):477-489, 1984.) and avocado (Wills; Sirivatanapa, 1988WILLS, R. B. H.; SIRIVATANAPA, S. Evaluation of postharvest infiltration of calcium to delay the ripening of avocados. Australian Journal of Experimental Agriculture, 28(8):801-804, 1988.).

Chitosan is a well-known natural and edible fruit coating material, because of its potential to inhibit fungal growth and extend the shelf life of fruits (Han et al., 2004HAN, C. et al. Edible coatings to improve storability and enhance nutritional value of fresh and frozen strawberries (Fragaria × ananassa) and raspberries (Rubus ideaus). Postharvest Biology and Technology , 33(1):67-78, 2004.). These beneficial effects may due to the reduction of fruit respiration metabolism (El Ghaouth; Ponnampalam; Boulet, 1991; Hagenmaier, 2005HAGENMAIER, R. D. A comparison of ethane, ethylene and CO2 peel permeance for fruit with different coatings. Postharvest Biology and Technology, 37(1):56-64, 2005. ), respiration rate and creation of a modified atmosphere within fruits, thus leading to an increase of CO2 concentrations inside fruit (Sivakumar et al., 2005SIVAKUMAR, D. et al. Effect of the combined application of chitosan and carbonate salts on the incidence of anthracnose and on the quality of papaya during storage. The Journal of Horticultural Science and Biotechnology, 80(4):447-452, 2005.) and reducing color changes of skin and flesh and increased the shelf life of fruits (Maftoonazad; Ramaswamy, 2005MAFTOONAZAD, N.; RAMASWAMY, H. S. Postharvest shelf-life extension of avocados using methyl cellulose-based coating. LWT - Food Science and Technology, 38(6):617-624, 2005.). In addition, chitosan acts as an inhibitor of various enzymes, leading to delay fruit senescence (Dutta et al., 2009DUTTA, P. K. et al. Perspectives for chitosan based antimicrobial films in food applications. Food Chemistry, 114(4):1173-1182, 2009.). Here, the positive effect of chitosan on shelf life extension of peach fruits was consistent with what was reported for various other fruits, such as papaya (Chutichudet; Prasit, 2014CHUTICHUDET, B.; PRASIT, C. Effects of chitosan or calcium chloride on external postharvest qualities and shelf-life of ‘Holland’ papaya. Fruit Journal of Agricultural Science, 6(11):282-280, 2014.), longan (Jiang; Li, 2001JIANG, Y.; LI, Y. Effects of chitosan coating on postharvest life and quality of longan fruit. Food Chemistry , 73(2):139-143, 2001. ), and fresh-cut strawberry (Campaniello et al., 2008CAMPANIELLO, D. et al. Chitosan: Antimicrobial activity and potential applications for preserving minimally processed strawberries. Food Microbiology, 25(8):992-1000, 2008.). Moreover, chitosan and calcium chloride, separately and in combination, were an effective preservative for the increase of shelf life of peach (El-Badawy, 2012EL-BADAWY, H. E. M. Effect of chitosan and calcium chloride spraying on fruits quality of Florida Prince peach under cold storage. Research Journal of Agriculture and Biological Sciences, 8(2): 272-281, 2012.), and mango (Chauhan; Agrawal; Raje, 2014CHAUHAN, S.; AGRAWAL, M.; RAJE, V. Efficacy of chitosan and calcium chloride on postharvest storage period of mango with the application of hurdle technology. International Journal of Current Microbiology and Applied Sciences, 3(5):731-740, 2014.).

Total soluble solid (TSS)

TSS percentage showed a steady increase in firmness, commensurate with the advance in the storage period (Table 6), this was regardless of treatments. In both seasons, untreated fruits recorded the highest TSS mean percentage, compared to all the other treatments, while the lowest mean percentage was obtained with the treatment of 2% CaCl2+1% chitosan.

Table 6:
Effect of some pre-harvest treatments on total soluble solid (%) of ‘Early Swelling’ peach fruits stored at 0±1 ºC during 2014 and 2015 seasons. Different letters indicate significantly different values by ANOVA followed by Duncan test at P≤0.05 (small letters refer to values recorded in each season, capital letters refer to mean values).

Increased TSS percentages throughout the storage period are presumably due to increased activity of enzymes responsible for starch hydrolysis to soluble sugars and can be caused by the decline in the amount of carbohydrates, pectines, partial hydrolysis of protein and decomposition of glycosides into subunits during respiration (Abbasi et al., 2009ABBASI, N. K. et al. Postharvest quality of mango (Mangifera indica L.) fruit as affected by chitosan coating. Pakistan Journal of Botany, 41(1):343-357, 2009.). Wongmetha and Ke (2012WONGMETHA, O.; KE, L. S. The quality maintenance and extending storage life of mango fruit after post-harvest treatments. World Academy of Science Engineering and Technology, 69:936-941, 2012.) reported that chitosan had no effect on TSS of mango fruits. A similar response was also showed in strawberry (Muñoz et al., 2008MUÑOZ, P. H. et al. Effect of chitosan coating combined with postharvest calcium treatment on strawberry (Fragara ananassa) quality during refrigerated storage. Food Chemistry , 110(2):428-435, 2008.).

Results of calcium as a pre-harvest treatment are in harmony with those mentioned by Montanaro et al. (2006MONTANARO, G. et al. Light influences transpiration and calcium accumulation in fruit of kiwifruit plants. Plant Science, 170:520-527, 2006.) on kiwifruit, Bhat et al. (2012BHAT, M. Y. et al. Effect of harvest dates, pre-harvest calcium sprays and storage period on physico-chemical characteristics of pear, cv. Bartlett. Journal of Agricultural Research and Development, 2(4):101-106, 2012.) on pear and El-Badawy (2012)EL-BADAWY, H. E. M. Effect of chitosan and calcium chloride spraying on fruits quality of Florida Prince peach under cold storage. Research Journal of Agriculture and Biological Sciences, 8(2): 272-281, 2012. on ‘Florida Prince’ peach.

Titratable acid (TA)

TA content decreased with the prolonging of the storage period (Table 7). As for treatments, in both seasons highest means of TA contents were obtained with all the combinations of CaCl2 and chitosan, while the lowest TA contents were recorded with 2% and 1% CaCl2 treatments in the first and second season, respectively. These results can be due to the reduction in metabolic changes of organic acids into carbon dioxide and water, as a result of reducing respiration rate, and therefore maintaining higher rates of acids. The results reported in this study are in agreement with those found by Goutam, Dhaliwal and Mahajan (2010GOUTAM, M.; DHALIWAL, H. S.; MAHAJAN, B. V. C. Effect of pre-harvest calcium sprays on post-harvest life of winter guava (Psidium guajava L.). Journal of Food Science and Technology, 47(5):501-506, 2010.) on guava, and El-Shazly et al. (2013)EL-SHAZLY, S. M. et al. Effect of some agro-chemicals preharvest foliar application on yield and fruit quality of ‘Swelling’ peach trees. Alexandria Journal of Agriculture Research, 58(3): 219-229, 2013. on peach.

Table 7:
Effect of some pre-harvest treatments on titratable acidity (%) of ‘Early Swelling’ peach fruits stored at 0±1 ºC during 2014 and 2015 seasons. Different letters indicate significantly different values by ANOVA followed by Duncan test at P≤0.05 (small letters refer to values recorded in each season, capital letters refer to mean values).

Total phenolic content (%)

It is worthy to note that total phenolic content increased with the advance in the storage period (Table 8). This was observed in both the studied seasons, irrespective of the treatments. As for tested treatments, in both seasons the highest total phenolic content was obtained by untreated fruits followed by 1% CaCl2, while the lowest total phenolic content was recorded by the treatment with 2% CaCl2+1% chitosan.

Table 8:
Effect of some pre-harvest treatments on total phenols (%) of ‘Early Swelling’ peach fruits stored at 0±1 ºC during 2014 and 2015 seasons. Different letters indicate significantly different values by ANOVA followed by Duncan test at P≤0.05 (small letters refer to values recorded in each season, capital letters refer to mean values).

As for the effect of chitosan treatments, it has been reported that pre-harvest chitosan spray enhanced total phenol content of table grapes during further storage at 0 °C (Meng et al., 2008MENG, W. et al. Physiological responses and quality attributes of table grape fruit to chitosan preharvest spray and postharvest coating during storage. Food Chemistry , 106:501-508, 2008.).

CONCLUSIONS

The effect of pre-harvest application of calcium chloride, chitosan and their combinations on storability and quality attributes of ‘Early Swelling’ peach fruits was investigated in this study. CaCl2 at 2% and chitosan at 1% concentrations proved to be effective in reducing weight loss (%), decay (%), and maintaining maximum firmness and lengthening shelf life. Fruit color (hº) was not affected by any of the treatments, while untreated fruits and calcium chloride alone with both the applied concentrations, were found to maintain higher total soluble solids (%), total phenolic content, and lower titratable acidity percentage (%).

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Publication Dates

  • Publication in this collection
    Mar-Apr 2017

History

  • Received
    06 Jan 2017
  • Accepted
    24 Feb 2017
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