Polyphenol oxidase, total phenolics and ascorbic acid changes during storage of minimally processed ‘California Wonder’ and ‘Quadrato d'Asti’ sweet peppers

A growing sector of ‘minimally processed’ vegetables market is represented by sweet peppers, whose quality may be affected by enzymatic activities. Among these, polyphenol oxidase leads to browning reactions, which is a major cause of quality loss. This research aimed at assessing the changes in PPO activity, total phenolics and ascorbic acid throughout a 30-days cold storage in minimally processed green (cv. ‘California Wonder’), yellow and red (cv. ‘Quadrato d’Asti’) sweet peppers. At day 0 PPO was active in red and yellow fruits but not in green ones, where it started to show relevant activity from the 3rd week of storage. At the end of the storage period (day 30), PPO activity was 1.36, 0.94 and 0.61 U/g d.m. in yellow, red and green peppers, respectively. Total phenols content was highest in green peppers, followed by red and yellow ones. In green fruits it increased up to the 3rd week of storage, decreasing afterwards, whilst in red and yellow fruits phenols content progressively declined after the 2nd week. Yellow fruits showed the highest ascorbic acid content, followed by red and green ones. Results confirm that green peppers ‘California Wonder’ are more suitable to minimal processing than yellow and red fruits.