Inhibitory effect of rice bran protein and its fractions on enzymatic browning in potato puree

Abstract

The protein was extracted from defatted rice bran (Oryza sativa L.) cv. Khao Pathum Thani 1, Khao Suphan Buri 1, Khao Dawk Mali 105, Khao Chinat 1 and Khao Gokho 15 using alkali extraction at pH 9.5, followed by precipitation at pH 4.5 to obtain rice bran protein extract (RBPE). The RBPE from Khao Dawk Mali 105 (K-RBPE) inhibited browning in potato puree more than the RBPE from the other cultivars. The protein concentration of K-RBPE was varied to 0%, 0.25%, 0.5%, 0.75%, 1.0%, 1.5% and 2.0% (g protein/100 mL extract). K-RBPE at 1.0% inhibited potato puree browning to a similar level as 1.5% and 2.0% during storage for 6 hr. Khao Dawk Mali 105 rice bran proteins were fractionated using the Osborne procedure and the effect was investigated
of its protein fractions on the inhibition of enzymatic browning in potato puree. The albumin rice bran protein fraction (Ab-RBPF) inhibited potato puree browning to a similar level as the glutelin fraction (Gt-RBPF) but the former had the highest potato polyphenol oxidase (PPO) inhibition among all the fractions. However, 1.0% K-RBPE inhibited potato puree browning more effectively than 1.0% Ab-RBPF. Furthermore, 1.0% K-RBPE had an inhibitory effect on browning similar to that of 10 mM ascorbic acid and 4-hexylresorcinol; and higher than for 10 mM ethylenediaminetetraacetic acid (EDTA) and citric acid; however, it was less effective than 10 mM cysteine and sodium metabisulfite. In addition, K-RBPE could inhibit potato PPO more effectively than Ab-RBPF,
citric acid and EDTA, respectively.