Bioactive polyphenols: their role in quality and storability of fruit and vegetables.

Phenolic compounds are plant secondary metabolites that are naturally present in essentially all plant material, including food products of plant origin. They are particularly prominent in fruit and vegetables where they are important in determining colour, appearance, flavour and taste. These compounds form one of the main classes of secondary metabolites, with a large range of structures: monomeric, dimeric and polymeric phenolics have been identified. Given a free choice the consumer selects foods with a low content of lignin (toughness) and/or tannin (astringency), but sometimes with a relatively high anthocyanin content (appearance and/or ripeness indicator). During the postharvest life of fruit and vegetables and the different technological treatments to which these plant tissues are submitted in order to extend their shelf life, some changes in secondary metabolism occur. These metabolic changes of phenolic compounds, often coupled with the activity of polyphenol oxidase, are responsible for some phenomena affecting the quality of stored plant commodities. In this connection two important aspects, related to the presence of phenolics, receiving increasing attention from biochemists, plant physiologists and food technologists, are the role of phenolics in browning reactions and the resistance mechanism against storage fungi. This paper emphasizes some aspects related to low temperature metabolism of endogenous phenolics in plant tissue under chill stress with reference to shelf life of cold stored fresh fruit and vegetables.