Woolliness Control and Pectin Solubiliz - PDF document

539 Woolliness Control and Pectin Solubiliz ation 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: 09, CEP: 13418 - 9000 - Piracicaba, Brazil. Keywords: Prunus persica, chilling in jury, 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 pe ctin s olubilization of ‘ Douradão’ peach fruit during cold storage were investigated. The treatments were: heat ing at 50°C during 1 and 2 hours (50°C/1h and 50°C/2h) ; heat ing at 20°C during 48 hours (20°C/48hs) and no n treated fruit (control) . Fruit were stored a t 1 º C for 30 days and were analyzed every 10 days ( plus 3 days at 25ºC) . Treatments with high temperatu re (50°C) advanced the onset of woolliness symptoms when compared with control treatment. The treatment with heating at 20°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 l ife of peaches under low temperature (Lurie and Crisosto, 2005). Thus, t he 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 (L ill et al., 1989; Zhou et al., 2000). 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., 2000 ). It has been hypothesized that the accumulation of high molecular weight pectin with a low degree of est erification may enable the binding of extracellular water into a gel - like form, causing the apparent lack of juice ( Zhou et al, 2000 ). 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 allevia te 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 sh ock treatments were used to prevent CI in many fruits including apples (Klein & Lurie, 1990), mangoes (McCollum et al., 1993 , Nair et al., 2001 ), citrus (Kluge et al, 2007), and peaches (Li and Han, 1998, Budde et al., 2002) Proc. VI International Postharvest Symposium Eds.: M. Erkan and U. Aksoy Acta Hort. 877, ISHS 2010 540 The purpose of this work was t o investigate the effect of prestorage treatment w ith high (50°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 50°C for 1 or 2 hours (50°C/1h and 50°C/2h); heating at 20°C during 48 hours (20°C/48hs) and no n - treated fruit (control). Fruit were stored at 1 ºC for 30 days and were analyzed each 10 days plus 3 days at 25 ±2 ºC shelf - life . The degree of CI (woolliness) was assessed by eye and gentle hand squeezing and fruit were divided into five classes: 0 – absent; 1 – very slight (VS); 2 – moderate (M); 4 – severe (E). The CI index recording the extent of damage on a 0 – 100 scale was calculated as follows: CI index = (1*N VS + 2*N S + 3*N M + 4*N E )/4 whe re 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 fr ozen flesh samples were ground in 25ml of 95% ethanol and then were incubated for 30min. at 4°C . T he samples were filter ed 3 times washing with 10ml of 75% ethanol . T he ethanol was discarded , and t he moist (no wet) p ulp was transfer ed to a 125ml erlenmeyer with 50ml 0,5% Versene solution, at pH 11,5 ( with 1N NaOH) and was incubated for 30min. (4°C). The pH was reduced to 5,0 - 5,5 ( with glacial acetic acid), 100mg of pectinase was added and the samples were incubated on a shaker for 1 hour at room temperature. Then, the samples were filter ed and the volume of filtrate brought to 100ml with 0,5% Versene solution. The water - soluble pectin (WSP) was obtained by extracting in ethanol as above and then incubating the pulp in 20ml of distilled water at room temperature with shaking. The samples were filtered and the filtrate brought to 100 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)*100 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 signifi cant 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 significa nt at 5% probability . RESULTS AND DISCUSSION Heat shock treatments with high temperature (50°C) advanced the onset of woolliness symptoms when compared with control treatment . Fruit treated with 50°C/1h and 50°C/2hs showed chilling injury (CI) index at 10 days of cold storage plus 3 days at 25°C (10+3) and unheated fruits showed the CI symptoms at 20 days of cold storage plus 3 days at 25°C (20+3). On t he other hand , the treatment with heating at 20°C/48hs reduced the woolliness symptoms ; fruits of this treatment had a 3 . 3 CI index only at 30 days of cold storage plus 3 days at 25°C (30+3) (Figur e 1A). These r esults were similar to those found by Vitti et al. (2007) for ‘Dourado 2’ peach submitted at heat shock treatment with 50°C/2hs and 20°C/48hs. Choic e and Lee (2001) noticed also that peach heated with 20°C/24hs showed low woolliness symptoms. The early woolliness symptoms in fruit treated with 50°C/1h and 50°C/2hs can be due the optimum temperature to pectinmet hy lesterase (PME) activity which is arou nd 40°C (Kluge et al., 2002) or 45°C (Ben - Arie and Lavee, 1971) , while the PG activity is inhibit ed at 541 high temperatures ( Kluge et al. , 2002). This imbalance of PME and PG activitie s can promote the accumulation of high molecular weigh t pectin with a low d egree of esterification , and may enable the binding of extracellular water into a gel - like form ( Ben Ar i e and Sonego, 1980 ; Zhou et al, 2000), causing a wooly texture . Regardless of treatment , there was an increase in pectin solubilization , water - soluble p ectins, and total pectic substances content, f rom the day 0 to the day 10+3 of storage (Figures 1B, 1C and 1D) . This was due to expose at 25°C witch promote s rapid ripening of fruit. After the 10+3 day , percent of pectin solubilization was gradually declin ed in woolly fruit (50°C/1h, 50°C/2hs and control treatments). Furthermore , pectin solubilizations in 2 4°C/48hs treated fruit increase d during storage (Figure 1B). There were no significant changes in water pectin - soluble content during storage, for all tr eatments (Figur e 1C). The total amount of pectin substances in 24°C/48hs treated fruit (non - woolly fruit) decreased at 30+3 days of storage. However, in control fruit and 50°C/1h or 50°C/2hs treatments (woolly fruit) there w as generally a rise in the pect ic content (Figure 1D). T he 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 th ese 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 t reatments with high temperatu re (50°C) advanced the onset of woolliness symptoms when compared with control treatment. On other hand treatment with heating at 20°C/48hs reduced the woolliness symptoms, bu t induced greater solubilization of pectin due greater decrease of total pectic substances content and consequently high loss of firmness (data no show n ) . Heat shock treatment needs further research to see if it can extend the postharvest storage life of p each fruits. ACKNOWLEDGEMENTS This research was financed by FAPESP: Fundação de Amparo à Pesquisa do Estado de S ão Paulo. (Process numbers: 2005/02179 - 1 and 2005/02422 - 3). Literature Cited A h med , A.R. and L abavitch , J.M. 1977. A simple method for accur ate determination of cell wall urinate conten t. J. Food Biochem. 1: 361 - 36. A ppleman , C. O. and C onrad , C. M. 1926 . Pectic constituents of peaches and their relation to softening of the fruit. Maryland Exp. Sta. Bull. 283: 1926 . B arkai - G olan , R. and P hill ips , D.J. 1991. Postharvest heat treatments on fresh fruits and vegetables fo r decay control. Plant Dis. 75 : 1085 - 1089. B en - A rie , R. and L avee , S. 1971. Pectic changes occurring in ‘Elberta’ peaches suffering from woolly breakdown. Phytochem.1 0 : 531 - 538 . B en - A rie , R. and S onego , L. 1980. 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H eat shock treatmen t 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 b ars indicate  S.E. ( n=4 ) A D C B