Microwave drying of ginger (Zingiber officinale Roscoe) and its effects on polyphenolic content and antioxidant activity.

The effects of microwave (MW) drying on the total polyphenol content (TPP) and antioxidant properties
of ginger extract (column extraction using 50% ethanol at room temperature) were evaluated using the
Folin–Ciocalteau’s method, 2, 2′-diphenyl-1-picryl-hydrazyl assay, reducing power, antioxidant capacity
and ferric reducing ability of plasma assay. The results were compared to that of the convective cross-flow
drying (CD) at 50 ± 4 °C. Extract yield, TPP content (59–80 mg GAE per g) of the MW-dried samples
increased with increase in MW power levels (PL 40, 60, 80 and 100), which might be as a result of MW
energy causing breakdown of cellular constituents. The MW-dried (PL100, 800W) extract showed the
highest quantity (1.5 fold) in TPP, [6]-gingerol content and antioxidant activity, when compared to the
CD extract. Hence, it might be concluded that the optimal MW PL for drying of ginger slices with respect
to retention of nonvolatiles such as TPP including [6]-gingerol was PL 100.