Total phenolic and flavonoid contents and antioxidant activity of ginger (Zingiber officinale Rosc.) rhizome, callus and callus treated with some elicitors

The present study was aimed at determining total phenolic and flavonoid contents and studying the antioxidant activity of ginger (<i>Zingiber officinale</i> Rosc.) rhizome and callus, 6-gingerol and 6-shogaol and callus treated with elicitors. Petroleum ether (PE) and chloroform: methanol (1:1, v/v) (CM) extracts were prepared by maceration. Highest total phenolic content was obtained from the CM extract (60.34 ± 0.43 mg gallic acid/g) of rhizome while callus showed lower content detected in the CM extract (33.6 ± 0.07 mg gallic acid/g). Flavonoids were only detected in rhizome (CM extract 40.25 ± 0.21 mg quercetin/g). Both rhizome extracts exhibited good antioxidant activity with higher activity recorded in PE extract (IC₅₀ value 8.29 ± 1.73 μg/mL). Callus extracts revealed lower antioxidant activity (IC₅₀ value 1265.49 ± 59.9 μg/mL obtained from CM extract). 6-gingerol and 6-shogaol displayed high antioxidant activity in both assays with IC₅₀ 4.85 + 0.58_DPPH and 5.35 ± 0.33_ABTS μg/mL for the former and IC₅₀ 7.61 ± 0.81_DPPH and IC₅₀ 7.05 ± 0.23_ABTS μg/mL for the latter. Treatment of callus with elicitors showed significant (p < 0.05) effects in enhancing phenolic content and related antioxidant activity. The highest significant increase in phenolic content (37% and 34%) and antioxidant activity in DPPH assay (34% and 30%) was observed in callus treated with 100 mg/L yeast extract and 50 mg/L salicylic acid respectively. Therefore, studying the effect of the elicitation of ginger cultured tissues in phenolic accumulation would be of immense importance for pharmacological, cosmetic and agronomic industries.