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.
Highlights
In the year 2018, the annual production of rice in Thailand was 11.08 million tons (Thai Rice Exporters Association, 2019)
All models of responses indicated that the P values were lower than 0.05 (except for that of ferric reducing antioxidant power (FRAP) (Y4) (p = 0.1857), which suggested that the model was adequately represented the experimental data
Optimization of the antioxidant extraction conditions applied to the cold-pressed defatted KDML105 rice bran using the mild SAW technology was successfully performed
Summary
In the year 2018, the annual production of rice in Thailand was 11.08 million tons (Thai Rice Exporters Association, 2019). Various phenolic compounds are found in rice bran, such as caffeic acid, ferulic acid, tannins, catechuic acid, sinapic acid, hydroxybenzoic acid, syringic acid, pcoumaric acid, and quercetin, as well as in rice (i.e., kaempferol, naringin, rutin, and catechin) (Tian et al, 2004; Shao et al, 2014; Setyaningsih et al, 2016). This research aimed at investigating the optimized conditions of mild-subcritical alkaline water extraction of cold-pressed defatted KDML 105 rice bran (CDRB) by providing the maximum antioxidant activity with a minimum of brown colour extract using response surface methodology (RSM). The phenolic profiles of the CDRB and the extract were elucidated
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