Bioprocessing of Brewers' Spent Grain Enhances Its Antioxidant Activity: Characterization of Phenolic Compounds and Bioactive Peptides.

Michela Verni,Elixabet Díaz-De-Cerio,Fabio Rinaldi,Sera Jacob,Rossana Coda,Carlo Giuseppe Rizzello,Erica Pontonio,Daniela Pinto,Vito Verardo,Annika Krona

doi:10.3389/fmicb.2020.01831

Abstract

Brewers’ spent grain (BSG) is the major by-product of the brewing industry which remain largely unutilized despite its nutritional quality. In this study, the effects of fermentation on BSG antioxidant potential were analyzed. A biotechnological protocol including the use of xylanase followed by fermentation with Lactiplantibacillus plantarum (Lactobacillus plantarum) PU1, PRO17, and H46 was used. Bioprocessed BSG exhibited enhanced antioxidant potential, characterized by high radical scavenging activity, long-term inhibition of linoleic acid oxidation and protective effect toward oxidative stress on human keratinocytes NCTC 2544. Immunolabelling and confocal laser microscopy showed that xylanase caused an extensive cell wall arabinoxylan disruption, contributing to the release of bound phenols molecules, thus available to further conversion through lactic acid bacteria metabolism. To clarify the role of fermentation on the antioxidant BSG potential, phenols were selectively extracted and characterized through HPLC-MS techniques. Novel antioxidant peptides were purified and identified in the most active bioprocessed BSG.

Highlights

Brewers’ spent grain (BSG), the major by-product of the beerbrewing industry, consists of the seed coat–pericarp–husk layers covering the original barley (Hordeum vulgare) grain (Lynch et al, 2016), and of insoluble residues deriving from other additional ingredients, such as raw or malted cereals, like maize (Zea mays) or wheat (Triticum durum and Triticum aestivum)
Cell density of presumptive lactic acid bacteria (LAB) in raw BSG (rBSG) was lower than 2 log cfu/g, while yeasts and total Enterobacteriaceae were 4.76 ± 0.03, and 3.58 ± 0.03 log10 cfu/g, respectively
At the end of fermentation, yeasts and Enterobacteriaceae cell density was lower than 4.12 ± 0.02 and 2.10 ± 0.03 log10 cfu/g, respectively, in all the BSG samples

Summary

Introduction

Brewers’ spent grain (BSG), the major by-product of the beerbrewing industry, consists of the seed coat–pericarp–husk layers covering the original barley (Hordeum vulgare) grain (Lynch et al, 2016), and of insoluble residues deriving from other additional ingredients, such as raw or malted cereals, like maize (Zea mays) or wheat (Triticum durum and Triticum aestivum). After extraction of the soluble compounds from the barley into the mash, the BSG is separated from the wort (liquid), which is boiled with hop and fermented. Brewers’ spent grain is essentially made of fiber (mainly hemicellulose and cellulose) which constitute half of its composition on dry basis; other important constituents are protein (up to 30%) and phenols. Arabinoxylans (AX), the main hemicellulose constituent, have a backbone of xylose residues, which can be substituted with arabinose residues (Lynch et al, 2016). BSG arabinoxylans include a significant water-extractable fraction and during enzymatic digestion they can release xylooligosaccharides with varying degree of polymerization (Wang et al, 2010)

Methods

Results

Conclusion