Antioxidant degradation kinetics in apples

Abstract

The effect of shelf storage under ambient conditions of cut apple dices on degradation of bioactive compounds such ascorbic acid, total phenols, antioxidant activity (% DPPH inhibition) and PPO activity were investigated. The results indicated that antioxidant activity declined significantly over 80 min storage of diced apples at ambient temperature. Similar trend was observed for ascorbic acid, total phenols and PPO activity. Ascorbic acid, total phenols and antioxidant activity degradation followed first-order kinetics where the rate constant (k) was found to be in range for all the thirteen cultivars, though initial ascorbic acid and phenol content varied in different apple cultivars. The reaction rate constant (k) for first order degradation ranged from 1.16 to 1.97, 0.89 to 1.29 and 0.37 to 1.54 for antioxidant activity, total phenols and ascorbic acid, respectively. This explains that antioxidant activity degrades at higher rate than total phenols and ascorbic acid, which also corroborates that antioxidant activity is affected by both total phenols and ascorbic acid content. In general, total antioxidant activity for apple dices kept for 80 min under ambient conditions exhibited lower values as compared to control.

Keywords: Antioxidant activity; Ascorbic acid; Degradation kinetics; Polyphenol oxidase activity; Total phenols.

Fig. 1

Degradation curves (% degradation) of antioxidant activity (expessed as % DPPH inhibition) for cultivars a ‘Starkrimson’, b ‘Royal Gala’ and c ‘Scarlet spur I’

Fig. 2

Degradation curves of total phenols for cultivars a ‘Scarlet Spur I’ and b ‘Super Chief’

Fig. 3

Degradation curves of PPO activity for cultivars a ‘Royal Delicious’, b ‘Scarlet Gala’ and c ‘Top Red’

Fig. 4

Change in ascorbic acid content of apple dices over 80 min shelf storage