Woolliness Control and Pectin Solubilization of Douradão Peach After Heat Shock Treatment

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1 Woolliness Control and Pectin Solubilization of Douradão Peach After Heat Shock Treatment F.F. Sasaki, T.S. Cerqueira, I. Sestari, J.S. del Aguila R.A. Kluge Department of Biological Science, University of São Paulo (ESALQ/USP), Av. Pádua Dias, 11 C.P: 9, CEP: Piracicaba, Brazil. Keywords: Prunus persica, chilling injury, cold storage, pectic substances, postharvest. Abstract Peach fruit ripens and senesces rapidly at room temperatures. The use of cold storage is limited by chilling injury which results in internal breakdown where internal browning and woolliness are the symptoms, and it is difficult to extend their storage life. In this study, effect of high and moderate temperatures on incidence of woolliness and changes of pectin solubilization of Douradão peach fruit during cold storage were investigated. The treatments were: heating at 5 C during 1 and 2 hours (5 C/1h and 5 C/2h); heating at 2 C during 48 hours (2 C/48hs) and non treated fruit (control). Fruit were stored at 1ºC for 3 days and were analyzed every 1 days (plus 3 days at 25ºC). Treatments with high temperature (5 C) advanced the onset of woolliness symptoms when compared with control treatment. The treatment with heating at 2 C/48hs reduced the woolliness symptoms, but induced greater solubilization of pectin and consequently high loss of firmness. Heat shock treatment appears problematic for the extension of the postharvest storage life of peach fruits. INTRODUCTION Peach fruit usually have a very short postharvest life at ambient temperature due to rapid ripening, drying, loss of firmness and high susceptibility to pathogens. Therefore, cold storage is used to slow these processes and decay development. However, chilling injury (CI) limits the storage life of peaches under low temperature (Lurie and Crisosto, 25). Thus, the storage of peaches at low temperatures for prolonged periods can induce a form of CI called woolliness (mealiness), characterized by a lack of juiciness and a dry, woolly texture (Lill et al., 1989; Zhou et al., 2). This flesh undesirable texture due to CI has been associated with an imbalance in cell wall metabolism. Woolliness has been attributed to impaired solubilization of pectic substances with accumulation of insoluble low methoxyl pectin of high molecular weight that combine with calcium forming calcium-pectate gel complexes (Ben-Arie and Lavee, 1971; Zhou et al., 2). It has been hypothesized that the accumulation of high molecular weight pectin with a low degree of esterification may enable the binding of extracellular water into a gel-like form, causing the apparent lack of juice (Zhou et al, 2). Watkins (1964) reported a considerable loss of total pectic substances in normally ripened fruit, and associated abnormal ripened of overstored fruit with an increase in total substances. However, Appleman and Conrad (1926) showed that the total amount of pectic substances in the fruit was fairly constant to irrespective of the ripening treatment. In the attempt to alleviate CI symptoms postharvest heat treatments has been used in different crops (Lurie, 1998). High temperatures have been reported to induce CI resistance (Barkai-Golan and Philips, 1991; Lurie, 1998) and delay ripening (Mitchell, 1986) in many fruit. Heat shock treatments were used to prevent CI in many fruits including apples (Klein & Lurie, 199), mangoes (McCollum et al., 1993, Nair et al., 21), citrus (Kluge et al, 27), and peaches (Li and Han, 1998, Budde et al., 22) Proc. VI International Postharvest Symposium Eds.: M. Erkan and U. Aksoy Acta Hort. 877, ISHS

2 The purpose of this work was to investigate the effect of prestorage treatment with high (5 C) and moderate (24 C) temperatures on the incidence of woolliness and changes of pectin solubilization of Douradão peach fruit during cold storage. MATERIAL AND METHODS Douradão peaches (Prunus persica) were harvested from a commercial orchard at pre-climateric but physiologically mature stage and selected for uniformity of size, maturity and freedom from defects. The treatments were: hot air heating at 5 C for 1 or 2 hours (5 C/1h and 5 C/2h); heating at 2 C during 48 hours (2 C/48hs) and non- treated fruit (control). Fruit were stored at 1ºC for 3 days and were analyzed each 1 days plus 3 days at 25±2ºC shelf-life. The degree of CI (woolliness) was assessed by eye and gentle hand squeezing and fruit were divided into five classes: absent; 1 very slight (VS); 2 moderate (M); 4 severe (E). The CI index recording the extent of damage on a 1 scale was calculated as follows: CI index = (1*N VS + 2*N S + 3*N M + 4*N E )/4 where N VS, N S, N M and N E were the percentages of fruit showing the different degrees of CI (Fernández-Trujillo and Artés, 1998). Total pectic substances and water-soluble pectin were extracted according the methods described by McCread and McComb (1952). For total pectic substances (TPS) 5g of frozen flesh samples were ground in 25ml of 95% ethanol and then were incubated for 3min. at 4 C. The samples were filtered 3 times washing with 1ml of 75% ethanol. The ethanol was discarded, and the moist (no wet) pulp was transfered to a 125ml erlenmeyer with 5ml,5% Versene solution, at ph 11,5 (with 1N NaOH) and was incubated for 3min. (4 C). The ph was reduced to 5,-5,5 (with glacial acetic acid), 1mg of pectinase was added and the samples were incubated on a shaker for 1 hour at room temperature. Then, the samples were filtered and the volume of filtrate brought to 1ml with,5% Versene solution. The watersoluble pectin (WSP) was obtained by extracting in ethanol as above and then incubating the pulp in 2ml of distilled water at room temperature with shaking. The samples were filtered and the filtrate brought to 1 ml with distilled water. The amount of total pectic substances and water-soluble pectin was measured according to Ahmed and Labavitch (1977). The pectin solubilization was calculated as follows: Solubilization = (WSP/TPS)*1 where WSP was the amount of water-soluble pectin and TPS was the amount of total pectic substances. The data were subjected to analysis of variance and the least significant differences were calculated for the completely randomized experimental design with four replicates of four fruit for each day of analysis. Differences between any two treatments greater than the sum of two standard deviations were considered significant at 5% probability. RESULTS AND DISCUSSION Heat shock treatments with high temperature (5 C) advanced the onset of woolliness symptoms when compared with control treatment. Fruit treated with 5 C/1h and 5 C/2hs showed chilling injury (CI) index at 1 days of cold storage plus 3 days at 25 C (1+3) and unheated fruits showed the CI symptoms at 2 days of cold storage plus 3 days at 25 C (2+3). On the other hand, the treatment with heating at 2 C/48hs reduced the woolliness symptoms; fruits of this treatment had a 3.3 CI index only at 3 days of cold storage plus 3 days at 25 C (3+3) (Figure 1A). These results were similar to those found by Vitti et al. (27) for Dourado 2 peach submitted at heat shock treatment with 5 C/2hs and 2 C/48hs. Choice and Lee (21) noticed also that peach heated with 2 C/24hs showed low woolliness symptoms. The early woolliness symptoms in fruit treated with 5 C/1h and 5 C/2hs can be due the optimum temperature to pectinmethylesterase (PME) activity which is around 4 C (Kluge et al., 22) or 45 C (Ben-Arie and Lavee, 1971), while the PG activity is inhibited at 54

3 high temperatures (Kluge et al., 22). This imbalance of PME and PG activities can promote the accumulation of high molecular weight pectin with a low degree of esterification, and may enable the binding of extracellular water into a gel-like form (Ben Arie and Sonego, 198; Zhou et al, 2), causing a wooly texture. Regardless of treatment, there was an increase in pectin solubilization, water-soluble pectins, and total pectic substances content, from the day to the day 1+3 of storage (Figures 1B, 1C and 1D). This was due to expose at 25 C witch promotes rapid ripening of fruit. After the 1+3 day, percent of pectin solubilization was gradually declined in woolly fruit (5 C/1h, 5 C/2hs and control treatments). Furthermore, pectin solubilizations in 24 C/48hs treated fruit increased during storage (Figure 1B). There were no significant changes in water pectin-soluble content during storage, for all treatments (Figure 1C). The total amount of pectin substances in 24 C/48hs treated fruit (non-woolly fruit) decreased at 3+3 days of storage. However, in control fruit and 5 C/1h or 5 C/2hs treatments (woolly fruit) there was generally a rise in the pectic content (Figure 1D). The changes in pectin solubilization were due to degradation of the total pectin substances content to free galacturonic acid (Figures 1B and 1D). Similar results were noticed for Ben-Arie and Lavee (1971) in normally ripening peach and woolly fruit. According these authors, total amount of pectic substances decreased in healthy fruit, due to a degradation of the soluble pectin in addition to a continued decrease in insoluble pectin, in woolly fruit they began to rise as a result of an increased quantity of the water-insoluble fractions (protopectin and pectates), and in spite of a continued decrease in water-soluble pectin. They suggest also that the chain length of the pectic substances in woolly fruit was considerably greater than in healthy fruit. Overall, our results showed that treatments with high temperature (5 C) advanced the onset of woolliness symptoms when compared with control treatment. On other hand treatment with heating at 2 C/48hs reduced the woolliness symptoms, but induced greater solubilization of pectin due greater decrease of total pectic substances content and consequently high loss of firmness (data no shown). Heat shock treatment needs further research to see if it can extend the postharvest storage life of peach fruits. ACKNOWLEDGEMENTS This research was financed by FAPESP: Fundação de Amparo à Pesquisa do Estado de São Paulo. (Process numbers: 25/ and 25/2422-3). Literature Cited Ahmed, A.R. and Labavitch, J.M A simple method for accurate determination of cell wall urinate content. J. Food Biochem. 1: Appleman, C. O. and Conrad, C. M Pectic constituents of peaches and their relation to softening of the fruit. Maryland Exp. Sta. Bull. 283: Barkai-Golan, R. and Phillips, D.J Postharvest heat treatments on fresh fruits and vegetables for decay control. Plant Dis.75: Ben-Arie, R. and Lavee, S Pectic changes occurring in Elberta peaches suffering from woolly breakdown. Phytochem.1: Ben-Arie, R. and Sonego, L Pectolytic enzyme activity involve woolly breakdown of stored peaches. Phytochem. 19: Brummell, D.A., Dal Cin, V.; Lurie, S., Crisosto, C.H. and Labavitch, J.M. 24. Cell wall metabolism during the development of chilling injury in cold-stored peach fruit: association of mealiness with arrested disassembly of cell wall pectins. J. Exp. Botany. 55:

4 Budde, C.O., Lucangeli, C.D.; PolentA, G. and Murray, R.E Golpe de altas temperaturas aplicado en poscosecha afectó la calidad de melocotón. ITEA 98. 2: Choi, J.H. and Lee, S.K. 21. Effect of pre-ripening on woollines of peaches. Acta Hort. 553: Fernández-Trujillo, J.P.; Cano, A. and Artés, F Physiological changes in peaches related to chilling injury and ripenig. Postharvest Biol and Technol. 13: Klein, J.D. and Lurie, S Prestorage heat treatment as a means of improving post storage quality of apples. J. Am. Soc. Hortic. Sci. 115: Kluge, R.A., Nachtigal, J.C., Fachinello, J.C. and Bilhalva, A.B. 22. Fisiologia e manejo pós-colheita de frutas de clima temperado. Rural, Campinas. Kluge, R. A., Jomori, M.L.L., Dall'Orto, F.C., Jacomino, A. P., Del Aguila, J. 27.Danos de frio e qualidade de frutas cítricas tratadas termicamente e armazenadas sob refrigeração. Rev. Bras. Frutic.29: Li, L.P. and Han, T Storage response of Okuba peaches after heat shock treatment. Acta Hort. 464: Lill, R.E., O Donoghue, E.M. and King, G.A Postharvest physiology of peaches and nectarines during. Hort. Rev. 11: Lurie, S Postharvest heat treatments. Postharvest Biol. and Technol. 14: Lurie, S. and Crisosto, C.H. 25. Chilling injury in peach and nectarine. Postharvest Biology. and Technol.37: McCollum, T.G., D Aquino, S. and McDonald, R.E Heat treatment inhibits mango chilling injury. HortScience. 28: McCready, R.M. and McCoomb, E.A Extraction and determinationof total pectic materials in fruits. Analytical Chem. 24: Mitchell, F.G Influence of cooling and temperature maintenance on stone fruit quality. Deciduous Fruit Grower. 36: Nair, S., Singh, Z. and Tan, S.C. 21. Heat treatments affect development chilling injury respiration, ethylene production and fruit quality of mango. Acta Hort. 553: Vitti, D.C.C., Kluge, R.A., Jacomino, A.P. and Lima, G.P.P. 27. Tratamento térmico para controle da lanosidade em pêssegos Douradão-2 refrigerados. Pesq. Agropec. Bras. 42: Zhou, H., Ben-Arie, R. and Lurie, S. 2. Pectin esterase, polygalacturonase and gel formation in peach pectin fractions. Phytochem.55;

5 Water soluble pectin (mg. 1g -1 ) Total pectic sustances (mg. 1g -1 ) Total pectic sustances (mg. 1g -1 ) Chilling injury index Pectin solubilization (%) Figures A C Controle 5 C/1h 5 C/2hs 2 C/48hs B Controle 5 C/1h 5 C/2hs 2 C/48hs D Controle 5 C/1h 5 C/2hs 2 C/48hs Control 5 C/1h 5 C/2hsControle 2 C/48hs 5 C/1h 5 C/2hs 2 C/48hs Figure 1. Heat shock treatment effects on changes in CI index (A), pectin solubilization (B), water-soluble pectin content (C) and total pectic substances content (D) in Douradão peach during cold storage and shelf-life. Vertical bars indicate S.E. (n=4) 543