Effect of drying techniques on the total phenolic contents and antioxidant activity of selected fruits

Abstract

The effect of drying techniques (ambient-drying and oven-drying) on the total phenolic contents and antioxidant activity of selected fruits (apple (Malus pumila, var. skysuper), plum (Prunus salicina, var. Fezele manani), apricot (Prunus armeniaca L, var. Nuri), strawberry (Fragaria ananassa var. Corona) and mulberry (Morus alba L, var. serrata) were studied. The antioxidant attributes of the fruits were evaluated following different colorimetric assays, while the composition of phenolic acids of the fresh fruits was analyzed by the reverse phase high performance liquid chromatography (RP-HPLC). The amounts of total phenolics (TP) were higher in mulberry samples followed by strawberry, plum, apple and apricot. The tested fruits exhibited appreciable radical scavenging capacity ranging from 58.7 to 82.2% and inhibition of linoleic acid peroxidation activity ranging from 61.8 to 86.1%. The RP-HPLC analysis of the fresh fruits revealed the presence of vanillic- (16.9), syringic- (12.7), p-coumaric- (2.30 to 47.5), ferulic- (0.9 to 32.9), sinapic- (3.10 to23.3), caffeic- (6.70-32.8), and gallic- (2.60 to 5.60) acids mg/kg of fresh fruit; p-coumaric acid being the most prominent component detected. The results of this study revealed that the amounts of TP and antioxidant activity of all the tested fruits, except those of apricot, decreased after drying treatment; relatively more pronounced decline was observed for the ambient-dried samples as against oven-drying. Therefore, it could be suggested that oven-drying at optimum temperature is comparatively a better means to dry and preserve fruits retaining maximum amounts of antioxidant compounds. Key words: Fruits, drying, DPPH scavenging, inhibition of per oxidation, phenolic acids, high performance liquid chromatography (HPLC).