Comparative Antioxidant Properties of Some Gingerols and Shogaols, and the Relationship of Their Contents with the Antioxidant Potencies of Fresh and Dried Ginger (Zingiber officinale Roscoe)

Abstract

Ginger (Zingiber officinale Roscoe) contains the biological properties of the major standard non–volatile pungent compounds of ginger, namely, [6]–, [8]–, and [10]– gingerols, as well as [6]– , [8]–, and [10]–shogaols. So far, the comparative antioxidant potencies among shogaols and gingerols have not been studied in detail and reported. Accordingly, this study aimed to examine and compare the antioxidant abilities of the six main compounds. Results showed that [6]–, [8]–, and [10]–gingerols, as well as [6]–, [8]–, and [10]–shogaols exhibited substantial in vitro antioxidant activities. The DPPH• , ABTS•+ , and FRAP assays results showed that the antioxidant abilities of [6]–shogaol were greatest among the six gingerols and shogaols studied (P< 0.05), and those of [6]–, [8]–, and [10]– shogaols were greater than those of [6]–, [8]–, and [10]–gingerols, respectively, which can be attributed to the presence of α, β–unsaturated ketones moieties. Moreover, the observation that the antioxidant abilities of [6]–gingerol were greater than those of [8]– and [10]–gingerols (P< 0.05) indicated that the short carbon chains of [6]–gingerol and [6]–shogaol played a significant role in making them more potent antioxidants than the other four longer carbon chain compounds. This finding can be attributed to gingerols undergoing dehydration transformations into shogaols during oven drying. Our results provided some new information on the antioxidant abilities of gingerols and shogaols. Keywords: α, β–unsaturated ketones moieties, Antioxidant potency, Gingerol, Shogaol, HPLC–UVD