THE COMPLEX AGING BEHAVIOUR OF BERRY FRUIT JUICES: CONSEQUENCES FOR BIOACTIVES CONTENT AND QUALITY

Abstract

It is well known that the processing of berry fruits into juices and nectars has a major impact on the concentration of secondary plant metabolites. The anthocyanins are more sensitive against aging than other polyphenols. The corresponding colour and quality change are limiting the shelf life and sensory acceptance by the consumer. The kinetics of anthocyanin degradation at 4 and 20°C are presented exemplarily for berry fruit juices. It is shown that the assumption of a first order reaction is only a rough approximation as many parallel and subsequent reactions can occur, leading to different aged pigments. Several mechanisms of anthocyanin-polyphenol reactions are known in fruit juices, among others the formation of pyranoanthocyanins and direct condensation to anthocyanin-tannin adducts. Furthermore, native anthocyanins can be bound to pectic polysaccharides during aging. The molecular fractionation by gel filtration revealed that the apparent molecular weights of these polymeric anthocyanin complexes can be higher than 10,000 Daltons. It can be expected that the resorption and bioavailability of anthocyanins is significantly influenced by these aging reactions. This leads to the question of realistic shelf life of the products.