Antioxidant capacity of fresh and dried rhizomes from four clones of turmeric (Curcuma longa L.) grown in vitro

Plant genotype, field conditions, and postharvest processing of turmeric (Curcuma longa L.) can alter the combinations of phytochemicals in rhizomes. We investigated the effects of drying upon the antioxidant potential of methanolic extracts from rhizomes of four clones of turmeric grown in vitro under controlled conditions. Antioxidant properties of microrhizomes were also compared with commercially available rhizome powder. The antioxidant capacities of extracts were assayed for their ability to scavenge the DPPH* radical and chelate ferrous iron. Tissue drying negatively affected the ability of extracts to scavenge the DPPH* radical in all four accessions tested, whereas the effect of tissue drying on ferrous iron chelating ability of extracts was cultivar specific. Fresh tissue extracts were more potent than extracts from commercially available turmeric powder in all cases for
both assays. The iron chelation assay revealed that extracts from recently dried tissue were significantly more potent than extracts from aged commercially available turmeric powder. DPPH* scavenging capacity of the dried tissue was usually of similar intensity to the commercially available powder with only one clone showing a significant difference in potency. Commercial drying methods may have negative effects on the antioxidants present in the rhizomes of turmeric. Genotypic selection minimized this effect. In vitro prepared rhizomes are a readily available source of fresh turmeric tissue from controlled environments irrespective of uncertainty associated with international outsource of seasonal, agricultural products.