Microbial Fermentation of Industrial Rice-Starch Byproduct as Valuable Source of Peptide Fractions with Health-Related Activity

Abstract

The rice-starch processing industry produces large amounts of a protein-rich byproducts during the conversion of broken rice to powder and crystal starch. Given the poor protein solubility, this material is currently discarded or used as animal feed. To fully exploit rice's nutritional properties and reduce this waste, a biotechnological approach was adopted, inducing fermentation with selected microorganisms capable of converting the substrate into peptide fractions with health-related bioactivity. Lactic acid bacteria were preferred to other microorganisms for their safety, efficient proteolytic system, and adaptability to different environments. Peptide fractions with different molecular weight ranges were recovered from the fermented substrate by means of cross-flow membrane filtration. The fractions displayed in vitro antioxidant, antihypertensive, and anti-tyrosinase activities as well as cell-based anti-inflammatory and anti-aging effects. In the future, the peptide fractions isolated from this rice byproduct could be directly exploited as health-promoting functional foods, dietary supplements, and pharmaceutical preparations. The suggested biotechnological process harnessing microbial bioconversion may represent a potential solution for many different protein-containing substrates currently treated as byproducts (or worse, waste) by the food industry.

Keywords: Lactobacillus spp.; bioactive peptides; protein hydrolysates; rice byproduct; rice protein.

Figure 1

Tricine SDS-PAGE (at incubation times 0, 24, 48, and 72 h), of rice protein byproduct (BR) not inoculated (control samples), and of BR incubated with strains LrC1122, Lp82, and LrPRRH, in three different experimental conditions (50 mL scale): (A) standard conditions; (B) with addition of fermentation substrate (FS); (C) with rice protein byproduct containing the solid fraction concentrated five times (BR5X), and addition of FS. Equal volumes of samples were loaded on gel.

Figure 2

Antioxidant activity by ABTS assay (mg AA eq/g of proteins, A), antihypertensive activity IC50 (mg/L, B), and anti-tyrosinase activity (mg KAeq/g, C), of peptide fractions 1 to 5 (1 = fraction with particle size higher than 0.2 μm; 2 = fraction with size below 0.2 µm and MW higher than 8 kDa; 3 = fraction with MW between 8 and 5 kDa; 4 = fraction with MW between 5 and 1 kDa; 5 = fraction with MW lower than 1 kDa) obtained from 1 L rice protein byproduct fermentation with strains LrC1122 (A1 to A5), Lp82 (B1 to B5), and LrPRRH (C1 to C5). N.D.: not detectable. Means followed by the same letter did not differ significantly (Tukey’s test, p > 0.05).