Postharvest Fruit Softening and Quality Management of Peach

Abstract

Peach being climacteric fruit ripe quickly after harvest and exhibit fast ripening at ambient conditions. Rapid postharvest fruit softening and quality deterioration limit its postharvest storage life. Therefore, this integrated study was carried out to understand the role of various factors, such as cultivars, harvest locations and application of pre-storage chemicals including salicylic acid (SA), oxalic acid (OA), putrescine (PUT) and CaCl2 to manage postharvest fruit softening and quality of peach. The degree of fruit softening was measured by determining the activities of fruit softening enzymes including pectin esterase (PE), endo-1-4-β glucanase (EGase), endo- polygalacturonase (endo-PG) and exo-polygalacturonase (exo-PG). Fruit quality parameters including activities of antioxidative enzymes [superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD)], total phenolic contents (TPC) and antioxidants scavenging activity (ASA), soluble solid contents (SSC), titratable acidity (TA), SSC: TA ratio and ascorbic acid contents were also determined during ripening and cold storage periods (35-days with 7-days interval). In the first study, the effects of cultivars and harvest locations on postharvest fruit softening and quality were evaluated. It was found that peach cv. ‘Flordaking’ exhibited reduced fruit softening and better fruit quality, as compared to cv. ‘Early Grand’ during cold storage (0±1°C and 80-85% RH) and under ambient conditions (25±2°C and 60-65% RH). Moreover, it was found that peach fruit harvested from Soan Valley, district Khushab revealed reduced fruit softening and activities of fruit softening enzymes with better fruit quality than fruit from Sillanwali, district Sargodha. Irrespective to peach cultivars and harvest locations, peach fruit exhibited full ripening (eating soft stage) on day-4 at ambient conditions. From this study, peach cv. ‘Flordaking’ harvested from Soan Valley were screened and selected for further trials. Among applications of different pre- storage chemicals, 1st trial was conducted regarding effects of SA (0, 2, 4 or 6 mM) on fruit softening and quality of ‘Flordaking’ peach fruit during ripening, under cold storage and at ripening following cold storage. Application of 6 mM SA significantly reduced the ethylene production and maintained higher fruit firmness during ripening and under cold storage conditions. Activities of fruit softening enzymes viz. PE, EGase, endo-PG and exo-PG were significantly reduced by application of SA in a concentration dependent manner. Peach fruit treated with higher concentrations of SA (6 mM) revealed relatively higher TPC, ASA, activities of antioxidative enzymes (SOD, POD and CAT) than untreated fruit. Moreover, peach fruit treated with 6 mM SA exhibited lower SSC: TA ratio, as compared to untreated fruit. The 2nd trial was carried out to check the effects of different concentrations of OA (0, 1, 2 or 3 mM) on fruit softening and quality of ‘Flordaking’ peach during ripening, under cold storage and at ripening followed by cold storage. Peach fruit treated with 3 mM OA showed reduced ethylene production, respiration rate and fruit softening. Reduction in fruit softening was associated with reduced activities of fruit softening enzymes (PE, EGase, endo-PG and exo-PG) in OA-treated fruit. Application of 3 mM OA significantly enhanced the TPC, ASA and activities of antioxidative enzymes viz. SOD, POD, CAT. During 3rd trial, effects of postharvest application of PUT (0, 0.5, 1 or 2 mM) were investigated on fruit softening and quality of ‘Flordaking’ peach during ripening, under cold storage and at ripening followed by cold storage. Application of 2 mM PUT significantly delayed ethylene production, reduced respiration rate and retained firm fruit, as compared to untreated fruit. PUT-treated (2mM) fruit exhibited reduced activities of fruit softening enzymes (PE, EGase, endo- PG and exo-PG). Moreover, low SSC: TA ratio, higher ascorbic acid contents, enhanced TPC, ASA and activities of antioxidative enzymes (SOD, POD and CAT) were exhibited by 2 mM PU- treated fruit. The 4th trial was carried out to study the effects of postharvest application of different concentrations of CaCl2 (0, 2, 4 or 6%) on fruit softening and quality of ‘Flordaking’ peach during ripening, under cold storage and at ripening followed by cold storage. CaCl2-treated fruit, at higher concentration (6% CaCl2) revealed reduced ethylene production and respiration rate. Application of 6% CaCl2 reduced fruit softening and activities of fruit softening enzymes including PE, EGase, endo-PG and exo-PG, in peach fruit. Higher TPC, ASA and activities of antioxidative enzymes (SOD, POD and CAT) were exhibited by 6% CaCl2-treated fruit. Although, the higher dose of CaCl2 (6%) was most effective in reducing fruit softening and improving quality of peach fruit but it caused toxicity symptoms on peach fruit. From above pre-storage trials best doses of different chemicals (6 mM SA, 3 mM OA, 2 mM PUT and 4% CaCl2) were screened and these were confirmed in another study. In confirmatory trial, it was found that among all tested anti-ripening chemicals, application of 2 mM PUT was more effective in reducing ethylene production, respiration rate and retaining higher fruit firmness. However, the activities of fruit softening enzymes were significantly suppressed by 4% CaCl2 treatment. In conclusion, application of 6 mM SA, 3 mM OA, 2 mM PUT or 4% CaCl2 were found beneficial to reduce fruit softening and activities of fruit softening enzymes, enhance antioxidative enzymes and retain better fruit quality of ‘Flordaking’ peach fruit upto 35-days of cold storage.