Effects of low preharvest temperature on scald susceptibility and biochemical changes in `Granny Smith' apple peel

Abstract

An over-tree mist system provided evaporative cooling of the `Granny Smith' apple fruit. The temperatures of fruit under mist, control (without mist) and air were recorded from 1 September until harvest. Fruit were harvested when 30, 60, 80, 100, 120 and 160 h at less than 10°C had been recorded. Fruit maturity indices (flesh firmness, soluble solids, titratable acidity, starch index, internal ethylene concentration and color), lipid composition, membrane permeability, antioxidant concentration and activity were evaluated at harvest and after 60, 120 and 180 days of storage at 0°C plus 7 days at 20°C. Superficial scald was evaluated after storage and a shelf life period. Maturity indices significantly changed during the harvest period. However, there was no significant difference between maturity indices of fruit under mist and control at the same harvest date. Fruit at the first harvest date without mist had accumulated 30 h at less than 10°C and 100% of them developed storage scald, while fruit of the same harvest date under mist had accumulated 60 h at less than 10°C and developed 82% scald. Superficial scald decreased to 16% on fruit exposed to T<10°C for 100 h and was negligible on fruit exposed to T<10°C for 120–160 h. Total lipids, waxes and fatty acids of apple peel increased with duration of temperature less than 10°C. Unsaturated fatty acids significantly increased on fruit with 100–160 h exposure to less than 10°C. Fruit exposed to less than 100 h at less than 10°C had higher electrolyte leakage of peel tissue discs than fruit with more than 100 h at less than 10°C. The concentration and activity of peel antioxidants significantly increased with the low temperature duration before harvest.