*4.2. Antioxidant Activity*

Another study by Prakash and Srinivasan [141] showed that ginger can significantly enhance the activities of antioxidant enzymes (*p* < 0.05), including superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), and glutathione-S-transferase (GST), in both gastric and intestinal mucosa in vivo. For eight weeks, eight male Wistar rats were fed ad libitum with a basal diet enriched with 0.05% ginger powder. Compared to the control group provided with the basal diet only, the ginger group showed 48%, 11%, 67%, and 50% stimulation in the activities of CAT, SOD, GST, and GR, respectively, in the intestinal mucosa. In rats subjected to ethanol-induced oxidative stress, ginger treatment demonstrated higher SOD, GST, and GR activities in the gastric mucosa by 35%, 39%, and 30%, respectively, compared to controls. Moreover, the ginger-fed group also had 56% higher mucin content of gastric mucosa than the ethanol-treated controls. In short, this study illustrated the gastrointestinal protective effects of dietary ginger against oxidative stress.

The gingerol-related polyphenols and diarylheptanoids derived from the rhizomes of ginger possess remarkable free radical scavenging activities [142]. However, the antioxidant potency may vary across ginger varieties. In an in vitro experiment, Oboh et al. [143] studied the antioxidant effects of two types of gingers (red and white) against free iron radicals in rat brains. Although both variants possessed antioxidant capacities against Fe2, the study found red ginger (*Z. officinale* var. Rubra) superior to white ginger (*Z. officinale* Roscoe) at inhibiting Fe2-induced lipid peroxidation and chelating Fe2, likely due to its higher ascorbic acid, phenol, and flavonoid contents.

Hinneburg et al. [144] demonstrated in another study that the contents of total phenols in various spices had significant positive correlations with their antioxidant properties in terms of iron reduction (r2 = 0.8871, *p* < 0.001) and inhibition of lipid peroxidation (r<sup>2</sup> = 0.7327, *p* < 0.01). Specifically, the hydro-distilled ginger extract showed relatively low Fe3 to Fe2 reducing activity and Fe<sup>2</sup> chelating capacity compared to basil, parsley, juniper, cumin, and fennel extracts. The reduced antioxidant activities were attributed to the low total phenols/extractable compounds ratio of only 7.8% for ginger versus 59.7% for basil. The water-based extraction method used in Hinneburg et al. [144] could not preserve the antioxidant activity of essential oils from ginger. Hence, the variety, extraction and processing methods can greatly affect the antioxidant properties of ginger.
