Total phenolics, total carotenoids, individual phenolics and antioxidant activity of ginger (Zingiber officinale) rhizome as affected by drying methods

This study was conducted to evaluate total phenolic content, antioxidant activity, total carotenoids and phenolic compounds of ginger (Zingiber officinale) rhizomes dried using different drying methods (oven, microwave, freeze and room-air drying). Freeze-dried ginger rhizomes exhibited significantly (p < 0.05) higher total phenolics (931.94 mgGAE/100 g), antioxidant activity (82.00%) and total carotenoids (13.17 mu g/g) than those dried using other techniques. Oven-dried ginger showed higher values for all individual phenolic compounds detected in this study as compared to those dried using other methods. The dominant phenolic compounds of dried ginger included (+)-catechin (250.02 mg/100 g), gallic acid (197.03 mg/100 g) and 3, 4-dihydroxybenzoic acid (116.07 mg/100 g). Drying of ginger rhizome using oven and freeze-drying methods my result in improved contents of bioactive compounds and higher antioxidant activity. Correlation analyses for biochemical composition of ginger rhizomes showed that total phenolics were positively correlated with antioxidant activity (r(2) = 0.973, p < 0.001).