engleski

Antioxidant activity, protein, peptide and polyphenol content of barley as affected by extraction pH

The aim of this study was to determine pH dependence of barley grain protein, peptide and polyphenol solubility and their contribution to the antioxidant activity of six barley varieties. Extracts prepared by extraction of wholemeal barley flour with Britton-Robinson buffer (pH range 3-11, 1 pH unit increment) and their corresponding TCA-supernatants prepared by TCA protein precipitation from the extracts, were examined for protein/peptide, free amino group and polyphenol content, as well as their antioxidant activity. Significant increase in the protein, free amino group and polyphenol content in wholemeal barley flour extracts were observed with the increase of pH of extraction, but antioxidant activity decreased at basic pH. Different pattern of pH dependence was observed for TCA supernatants. TCA soluble peptide content was found to be highest at the lowest pH of extraction, free amino group content and antioxidant activity slightly increased with pH increase, while polyphenol content showed “S” shaped curve of pH dependence. The most striking was the difference in polyphenol content between extracts and their corresponding TCA-supernatants, being higher in supernatants than in extracts at basic pH. Similarly was observed for antioxidant activity, which was found to be higher in supernatants than in extracts at basic pH. This indicates that barley proteins soluble at basic pH significantly interfere with the polyphenols detection and probably act as quenchers of antioxidant activity.

antioxidant activity; barley grain; free amino groups; peptide; polyphenols; protein; solubility

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