Anthocyanin Fluorescence for Monitoring Oxidation of the Chokeberry Fruit During Drying and Storage of Fruit Lyophilizates.

The appearance of the "oxidation band" in the fluorescence spectrum of anthocyanins is an indicator of oxidative deterioration of anthocyanins and can be a useful preliminary index of food freshness. Chokeberry (Aronia melanocarpa) fruit, rich in anthocyanins, can be subject to drying or lyophilization for domestic or industrial applications. The study was aimed at determining whether the measurement of fluorescence of dried chokeberry extracts can provide information on the extent of anthocyanin oxidation during prolonged drying at 60°C, and if fluorescence of fruit extracts can monitor anthocyanin oxidation during storage of the lyophilizates at various temperatures under air exposure. The increase in the fluorescence intensity of the extracts of chokeberry fruits or their lyophilizates at the "oxidation band" was a regular function of the time of fruit drying and the time of lyophilizate storage at 22°C and 37°C, confirming the usefulness of this parameter for estimation of oxidative changes in dried fruits and their lyophilizates. However, fluorescence of whole fruits, pulverized fruits and pulverized lyophilizate did not show a regular increase as a function of the time of fruit drying and lyophilizate storage, apparently due mainly to the effects of light scattering. The results point to the necessity of controlling the drying process of chokeberry fruits and storing their lyophilizates at ambient or higher temperatures with air access to avoid anthocyanin oxidation.