CARATTERIZZAZIONE DELLE PRINCIPALI ATTIVITA' OSSIDASICHE COINVOLTE NELL'IMBRUNIMENTO DELLE FRAGOLE

Strawberries represent one of the most used berries by food industry and their susceptibility to post-harvest decay mainly depends by endogeneous enzymatic reactions carried out by polyphenol oxidase (PPO) and peroxidase (POD). In present work the characterized oxidases were extracted from two different varieties of strawberry fruit (Fragaria x ananassa D. cv. ‘Elsanta’ and Fragaria vesca L. cv. ‘Madame Moutot’). In all cases the enzymes followed the Michaelis-Menten kinetics but showing different values of kinetics parameters Km and Vmax. Physiological pH of fruit at red ripe condition negatively affected the expression of both oxidases, except for PPO from ‘Madame Moutot’ that showed the highest residual activity (68% of the maximum). POD from both cultivars resulted much more thermolable than PPO and its activation energy resulted much lower than PPO. Results obtained from D-glucose and D-fructose inhibition tests evidenced a decreasing course of PPO and POD activities from both cultivars as sugars concentration in the assay medium increased. PPO and POD from cv. ‘Elsanta’ were very well correlated with the parameter L* (r2 =0.86 and 0.89 for PPO and POD, respectively) and Hue angle (r2 =0.85 and 0.93 for PPO and POD, respectively). These results confirmed the involvement of PPO in browning of all samples tested, while only the commercial cv. ‘Elsanta’ showed a good correlation between POD activity and color loss of the strawberries.