Phenolic composition and antioxidant potential of dry sweet cherry fruits.

Abstract

Three sweet cherry cultivars, ‛Carmen’ (early-medium ripening cultivar), ‛Kordia’ (late ripening cultivar), and ‛Regina’ (very late ripening cultivar) were studied for total phenolic content (TPC), total flavonoid content (TFC), total phenolic acids content (TPAC) and antioxidant potential. All cultivars have large to very large fruits with an average weight of 8 to 10 g. The fruits were picked at the full maturity stage, in the cherry orchard at the experimental farm "Radmilovac" of the Faculty of Agriculture in Belgrade. Drying was performed at the experimental dryer using the convective drying method (two constant air temperatures, 70 and 80 °C, air flow speed 4 m/s) until a constant mass was reached. The extracts of the dried fruits were prepared with methanol (1:5 ratio) in an ultrasonic bath (240 W, 35 kHz) at 25°C for 30 minutes. The results of TPC, TFC and TPAC were expressed as corresponding equivalents per gram of dry extract (gallic acid GAE/g, quercetin QE/g, and caffeic acid CAE/g, respectively). The antioxidant potential of the extracts was evaluated by total antioxidant capacity (TAC), DPPH radical and ABTS radical-cation scavenging potential assays and expressed either as equivalents of ascorbic acid (AA) or as IC50 values for DPPH⦁ and ABTS⦁+ assays. The highest TPC was determined in the extract of ‛Kordia’ fruits dried at both temperatures (70 °C - 12.59 and 80 °C - 10.89 mg GAE/g), but without significant differences (p>0.05). The ‛Kordia’ cultivars dried at 70 °C had the highest TFC content (1.10 mg QE/g), which was significantly different from that dried at 80 °C (p<0.05), while no flavonoids were detected in ‛Regina’ and ‛Carmen’ (dried at 70 °C). On the other hand, cultivars ‛Carmen’ and ‛Regina’ dried at 70 °C had the highest TPAC, 3.49 and 3.96 mg CAE/g, respectively. In all three assays, the extract of ‘Kordia’ cherry fruits dried at 70°C stood out with the highest antioxidant potential, and differed significantly from the extract of the sample dried at 80 °C (p<0.05). The opposite trend was observed for ‛Carmen’ and ‛Regina’ cultivars, however with no significant differences between extracts of samples dried at 70 and 80 °C (p>0.05). The increased contents of polyphenols, flavonoids and phenolic acids in the extract of ‛Kordia’ cherry fruits were associated with the lower drying temperature of the fruits.