Background and methodology:
Enzymatic browning of fruit and raw vegetables is related to oxidation of phenolic compounds into quinones, which are later poly-merized to brown, red and black pigments. In this study, polyphenoloxidase (PPO) activity and total polyphenol content were tested in organically and conventionally grown peach (Prunus persica L., cv. Regina bianca) and pear (Pyrus communis L., cv. Williams), in order to evaluate the existence of a relationship between these parameters and of differences between fruits obtained with the two cultivation practices. Whole fruits (cortex and peel) of peach and pear were obtained from an experimental orchard at Rome. Organic fruits were obtained on three different grounds: subterranean clover (sample A), spontaneous weed cover (sample B) and tilled (sample C). From the latter soil, the conventionally grown fruits were produced. Immediately on arrival, parts of the fruit samples were lyophilized (for determination of total polyphenols) and parts were frozen at -40�C (for activity assays). Total polyphenols were determined by the spectro- photometric method of Joslyn.
All organic peach samples showed a highly significant increase in polyphenols (milligram equivalents of tannic acid/100 g fresh sample) compared with conventional peaches, while of the three organic pear samples, samples B and C displayed an increased polyphenol content with respect to the conventionally grown sample. Activity of PPO, extracted in appropriate conditions and tested towards chlorogenic and caffeic acid, was significantly higher in most of the organic peach and pear samples analyzed with respect to the conventional samples.
Carbonaro, M., & Mattera. M. (2001). Polyphenoloxidase activity and polyphenol levels in organically and conventionally grown peach (Prunus persica L., cv. Regina bianca) and pear (Pyrus communis L., cv. Williams). Food Chemistry, 72, 419-424.