Application of mild-subcritical alkaline water extraction: optimum condition for phenolic antioxidant extracted from cold-pressed defatted KDML 105 rice bran and its phenolic profile

Abstract

This research was aimed at optimizing the process of the mild-subcritical alkaline water (pH 9.5) extraction (mild SAW) of cold-pressed defatted Khao Dawk Mali 105 rice bran (CDRB) in order to achieve the maximum antioxidants with minimal brown colour. Response surface methodology and central composite design were performed with two variables: extraction temperature (107-129°C) and time (21-149 mins). The elucidated optimum conditions were 119°C and 85 mins with predicted response values: the total phenolic content of 16.9 mg gallic acid/g; protein of 64.3 mg/g; an ABTS radical scavenging activity of 14.4 mg Trolox/g; a browning index of 0.41; and reducing sugar of 62.0 mg/g. Proto-catechuic acid and p-coumaric acid were major phenolic compounds in the CDRB, while trans-ferulic acid, proto-catechuic acid, and p-coumaric acid were all abundant in the mild SAW extract. The results confirmed that the mild SAW extraction process for antioxidants is an environmentally friendly approach, which can increase the release of value-added compounds from rice bran residues.