Evaluation of the In Vitro Bioactivities’ Profiles of Brewers’ Spent Grain Protein and Hydrolysates with and without Cellulase Pretreatment

Abstract

Brewer’s spent grain is the residue left after the separation of wort during the beer-brewing process. Although this by-product has been reported to have a high protein content, it is normally treated as waste. This work aims to isolate bioactive hydrolysates from BSG, and then explore their bioactivities. Two groups (A and B) of BSG were subjected to protein extraction using the alkaline extraction method at pH 12, where group A was pre-treated with cellulase, while group B was not pre-treated and was directly extracted. The final isolate yielded 50.18 ± 1.22% recovery of the BSGP from group A and 66.41 ± 0.37% recovery from group B. RP-HPLC profiles showed that the extracted BSGPs are mainly hydrophilic proteins. The proteins extracted by the two methods were hydrolyzed enzymatically using Alcalase and α-chymotrypsin. The hydrolysates obtained displayed blood pressure regulation activity and antioxidant properties, when assayed with angiotensin-converting enzyme assay, 2,2-diphenyl-picryl-hydrazyl assay, and ferric antioxidant power assay. It can be concluded that it is possible to extract good quality proteins from BSG and this by-product presents potential as a source for the extraction of a variety of proteins that might be of interest to the food industries.

Extraction, Composition, Functionality, and Utilization of Brewer’s Spent Grain Protein in Food Formulations

“…As wet BSG obtained after the brewing process contains high amounts of moisture (75–80%); it is first dried to enhance the shelf life, reduce the volume, and ease material handling [ 35 ]. After drying, a variety of extraction methods and conditions have been reported to obtain protein products from BSG ( Table 3 ), with alkaline extraction being the most commonly used approach [ 36 , 37 , 38 , 39 , 40 ]. Most extraction methods, in general, include two steps: protein solubilization followed by protein recovery.…”

“…The BSG is first mixed with water-based solutions, which may contain a variety of reagents that help disintegrate the BSG matrix and decrease interactions between proteins and other macromolecules, thus facilitating their release. The solubilized proteins are then recovered either through centrifugation and isoelectric point precipitation [ 37 , 38 , 40 , 41 , 42 ] or membrane filtration [ 39 , 43 , 44 , 45 ].…”

“…A set of different pretreatments are often used before extraction, to assist protein release from the BSG matrix. Defatting, particle size reduction through milling or shearing, enzymatic hydrolyzation, and ultrasound are the most common pretreatments, with the latter two also being used independently as ‘chemical free’ alternatives to traditional alkaline extraction ( Table 3 ) [ 37 , 38 , 39 , 40 , 41 , 42 , 44 , 47 , 48 , 54 ]. Mixed results, however, have been reported after studying the effects of these pretreatments.…”

“…Alkaline extraction is a well-studied method to recover proteins from different kinds of agricultural sources, including BSG. In this method, the alkaline conditions facilitate protein solubilization by altering protein structure, charge, and, consequently, interactions [ 36 , 37 , 38 , 39 , 40 , 44 , 47 , 48 , 58 ]. A wide range of extraction yields (~18 to 82%) and protein purities (37 to 69%) have been obtained through this method upon varying the process conditions, as shown in Table 3 .…”

“…Multi-step extraction approaches such as acid−alkaline and enzyme−alkaline techniques did not necessarily demonstrate a positive effect on extraction yield. For example, while an increase in protein recovery from ~50 to 65% was observed upon adding an acid pretreatment prior to alkaline extraction [ 46 ], cellulase pretreatment prior to alkaline extraction decreased protein recovery from 66% to 50% [ 40 ]. These results show that processing parameters have to be carefully selected to achieve and maintain optimum protein solubility.…”