Quality attributes and biochemical changes in white and colored table grapes as influenced by harvest maturity and ambient postharvest storage

Abstract

Maturity is a key factor that determines fruit quality and shelflife. Determination of the correct harvest stage is always challenging in non-climacteric fruits, and more complex with grapes because of varietal and climatic variations. Thus, the current study was conducted to determine the effect of different maturity levels on berry composition and postharvest quality of table grapes. Three grape cultivars (‘Sultanina-C’, ‘Flame Seedless’ and ‘NARC Black’) were harvested at early (M1) mid (M2) and late (M3) maturity stages, based on berry color development. Harvested fruits were kept at ambient conditions (25°C with 60-65% Relative Humidity) for physico-chemical and antioxidant evaluation until onset of decay. Results indicated that, regardless of storage duration, the fruit harvested at the second (M2) or third (M3) maturity stages exhibited significantly lower weight loss and berry shattering with better skin color (L*, a*, b*). Titratable acidity (TA) was significantly lower while total soluble solids (TSS), pH and TSS:TA ratio were significantly higher at M3. No significant difference in ethylene production was recorded in maturity stages but a significant linear increase was observed during ambient storage whereas, respiration rate was found to be higher in fruit harvest at early stage of maturity (M1) that increased gradually during ambient storage and start decreasing at the end of shelf life. Total phenolic content (TPC), antioxidant scavenging activity (ASA), and activities of antioxidative enzymes like superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), and polyphenol oxidase (PPO) significantly decreased with increasing maturity level. During ambient storage for 4 days, ASA and activity of SOD, CAT and PPO increased initially and then decreased, while TPC and POX activity decreased linearly. ‘NARC Black’ grapes had higher TPC, ASA, anthocyanins, SOD and POX than the other cultivars. Conclusively, grapes harvested at M3 exhibited better fruit physico-chemical quality attributes with least antioxidative characters which was higher at M1 irrespective to white or colored table grapes at ambient storage.