Valorization of Heat-Treated Brewers' Spent Grain Through the Identification of Bioactive Phenolics by UPLC-PDA and Evaluation of Their Antioxidant Activities.

Md Jiaur Rahman,Michael Eskin,Lovemore Nkhata Malunga,Usha Thiyam-Hollander,Sijo Joseph Thandapilly,Peter Eck

doi:10.3389/fnut.2021.634519

Md Jiaur Rahman, Michael Eskin + Show 4 more

Open Access

https://doi.org/10.3389/fnut.2021.634519

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Abstract

Thermal processing not only disrupts cell membranes and cell walls, but also cleaves covalent bonds releasing low molecular phenolic. This study examined the impact of various heat treatments (100, 140, and 160°C) on the composition of phenolic acids and antioxidant activities in extracts obtained from defatted brewers spent grain (BSG) meal. Heating BSG at 160°C resulted in a 2-fold increase in total phenolic content [TPC, 172.98 ± 7.3 mg Gallic acid equivalent (GAE)/100 g defatted meal] and total flavonoid content [TFC, 16.15 ± 2.22 catechin equivalents (CE)/100 g defatted meal] compared to the untreated BSG extracts. The antioxidant activities of treated BSG extracts, determined by radical scavenging and ferric reducing antioxidant power (FRAP) were significantly (p < 0.5) higher than the corresponding untreated BSG extracts. Eleven phenolic acids were identified and quantified in BSG extracts by Ultra Performance Liquid Chromatography with Photodiode Array (UPLC-PDA). The amounts varied significantly (p < 0.05) depending on the degree of toasting BSG was subjected to. Chlorogenic acid, an ester of caffeic and quinic acid was the predominant phenolic acid present in all fractions. Significant (p < 0.05) increases in TPC, TFC, individual phenolic acids and antioxidant activity were observed in BSG extracts exposed to increasing oven temperatures. These results confirm the ability of heat processing to release bioactive phenolic from their bound forms thereby enhancing the phenolic acids and the digestibility of BSG meal in the intestinal tract.

Highlights

Brewers’ spent grain (BGS), a by-product of brewing industry, is produced from barley malt during the production of wort
An almost 2-fold increase in total phenolic content (TPC) was observed at 1600C while brewers spent grain (BSG) treating at 140◦C showed 1.5-fold increase in TPC compared to the sample heated at 100◦C or the control
This finding was in agreement with previous studies that reported TPC increased significantly in citrus peel, camelina meal, and Pleurotus eryngii when heated at the higher temperatures [28,29,30,31]

Summary

Introduction

Brewers’ spent grain (BGS), a by-product of brewing industry, is produced from barley malt during the production of wort. According to the literature, ∼20 kg (WB) of BSG are produced during the production of 100 L beer which represents around 31% of original malted barley weight [1,2,3]. BSG is an inexpensive and underutilized by-product available in large amounts throughout the year [2, 3]. It is good source of protein (20% w/w), fiber (70 % w/w) and essential amino acids. The potential of BSG as a functional ingredient and a good source of health-promoting bioactive is gradually being recognized. BSG’s polyphenols, arabinoxylans, and protein hydrolysate are receiving increasing attention because of their potential health benefits [3, 5]

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