Composition and Antioxidant Activity of Different Forms of Phenolic Compounds from Sorghum Bran
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Abstract:
The different forms of phenols, including free, soluble esterified, soluble glycosidic, insoluble-bound esterified, and insoluble-bound glycosidic polyphenols were extracted from sorghum bran. The content of 15 phenolic compounds were determined by high performance liquid chromatography. The antioxidant activities of different forms of phenols were evaluated by measuring the 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and superoxide (O2-) radical scavenging activities and Fe3+ reducing ability power. The results showed that the content of free, soluble esterified, soluble glycosidic, insoluble-bound esterified, and insoluble-bound glycosidic phenols in sorghum bran were 645.27, 138.57, 48.67, 118.92, and 176.06 mg GAE/100 g, respectively. The highest phenolic content were found in ferulic acid (39.04%) and salicylic acid (28.04%), while 3,4-dihydroxybenzoic acid showed the lowest phenolic content (0.09%). Ferulic acid was mainly found in insoluble-bound form, and the content of isochlorogenic acid was relatively high in the soluble phenolic compounds, while salicylic acid had the highest content among the free phenolic compounds. In different antioxidant systems, there were slight differences in the antioxidant activities of phenols in different forms. In general, soluble esterified, insoluble-bound esterified, and insoluble-bound glycosidic phenols possesses relatively high antioxidant activities, while free phenols have relatively low antioxidant activity, in spite of having the highest phenol content.
