Phenolic compounds and related enzymes are not rate-limiting in browning development of fresh-cut potatoes

The effect of minimal processing on polyphenol oxidase (PPO), peroxidase (POD), phenylalanine ammonia-lyase (PAL), and phenolic compounds was studied in five potato cultivars (Agria, Cara, Liseta, Monalisa, and Spunta). Minimal processing caused an overall increase in PPO, POD, and PAL activities. The isoform pattern of PPO was the same for all of the cultivars before and after processing. No latent PPO was detected. The isoperoxidase pattern was approximately the same among cultivars. An increase in POD activity was related to the specific induction of an acidic isoperoxidase. PAL showed an induction pattern characterized by the presence of a maximum peak of activity after 4 days of processing for all of the cultivars. The sequence of browning susceptibility of potato cultivars was as follows: Monalisa > Spunta > Liseta > Cara > Agria. Browning development was only partially correlated to PAL activity (only during the first 4 days after wounding). However, this correlation could not explain the above sequence of browning susceptibility. Minimal processing caused an increase of chlorogenic acid, whereas tyrosine content remained unchanged. In summary, no significant correlation was found between either rate or degree of browning and any other biochemical and physiological attribute investigated (PPO, POD, hydrogen peroxide, ascorbic acid content, and initial phenolics content as well as total and individual phenolics accumulation).