The influence of postharvest calcium chloride treatments on apple (Malus domestica Borkh) fruit quality and polyphenol oxidase, peroxidase, and pectin methyl esterase activities

The purpose of this study was to determine the following; (1) optimum postharvest, pressure infiltrated calcium chloride (CaCl₂) treatments for fresh and processed 'Golden Delicious' and 'Delicious' apple (Malus domestica Borkh.) fruit quality, and (2) to examine the effect of increased calcium concentrations on enzymes associated with softening (pectin methyl esterase), browning (polyphenol oxidase), and senescence (peroxidase). Apple tissue calcium concentrations were determined and fresh and processed fruit qualities were evaluated at harvest and after three and six months in storage at 1°C. PPO and POD activities were determined at harvest and after three and six months in storage at 1°C. HVE activity was measured at harvest and after two, four, and six months in storage at 1°C.

Firmness, ascorbic acid content (mg·100g fresh wt⁻¹), and total phenols (μg·g fresh wt⁻¹) were maintained at levels comparable to initial values as calcium concentrations increased for both testing intervals. Soluble solids (%) and titratable acidity (% malic acid) were not significantly affected by any calcium treatment for either cultivar or storage interval.

Sauce made from apples with calcium concentrations of 2000 μg·g dry wt⁻¹ for 'Golden Delicious' and 1200 μg·g dry wt⁻¹ for 'Delicious' tended to flow less (lower consistency values) and have less free liquid. Sauce made from 'Golden Delicious' after six months of storage did not meet USDA requirements for sauce grades probably because the apples were in an advanced stage of senescence. A decrease in luminosity (lower 'L' Hunter Colorimeter values) was observed in applesauce made from calcium treated apples at both time intervals. Apple juice produced from calcium-treated fruit reflected a lighter colored juice at both time intervals as expressed by higher 'L' values.

PPO activity, (δOD) min¹⁻ mg protein¹⁻, decreased as calcium concentrations increased at both testing intervals. PPO activity, after six months in storage, was higher than that at three months. POD activity, (also measured as δOD·min¹⁻·mg protein¹⁻) increased as calcium concentration was increased at both time intervals, and activity in both cultivars was higher after six months than after three months in storage. PME activity (meq H⁺·min¹⁻·mg protein¹⁻) decreased as calcium concentrations were increased at all three testing intervals and reached highest activity after approximately four months in storage.