From plums to prunes: Influence of drying parameters on polyphenols and antioxidant activity

Prunes, which are industrially obtained by dehydrating fresh plums at 85-90 degreesC for 18 h, contain higher levels of phenolic compounds than most other fruits. Prune phenolics have shown beneficial effects on human health. Reports are available in the literature on ascorbic acid, phenol composition, and antioxidant activity of fresh plums and prunes, but there is a lack of publications on the influence of drying parameters on the phenolic compounds and antioxidant activity. A study was carried out on two plum cullivars using two sets of air-drying temperatures: (i) air temperature at 85 degreesC until 50% of prune moisture level and then the temperature was lowered to 70 degreesC; (ii) air temperature at 60 degreesC. Whole fresh and dried fruits were assessed for phenolics (catechins, hydroxycinnamic acids, anthocyanins, and flavonols), ascorbic acid, and antioxidant activity (all parameters were calculated on a dry mat-ter basis). Analysis of data shows that chlorogenic and neochlorogenic acid changes were affected by both process parameters and cultivar. Drying destroyed anthocyanins, and there was a significant decrease in flavonols. Ascorbic acid was drastically reduced in relation to process temperature. The most striking result was that drying at 85 degreesC doubled antioxidant activity in both cultivars, while contradictory results were found for 60 degreesC processed plums.