Generation and characterisation of novel health enhancing ingredients from brewers’ spent grain (BSG)

The primary objective of this study was to evaluate the potential of pale and black brewers’ spent grain (BSG), brewery barley by-products, as starting materials for the generation of protein-enriched isolates (BSG-PI). A second objective was to characterise the resulting BSG-PI in terms of their techno- and biofunctional properties. The effect of enzymatic hydrolysis of BSG-PI, using commercially available proteolytic preparations, on the techno- and biofunctional properties was also studied. The technofunctional properties studied were Nitrogen solubility, heat stability, viscosity, turbidity, and emulsion and foaming properties. The biofunctional properties studied were α-amylase, α-glucosidase, angiotensin converting enzyme (ACE) and dipeptidyl peptidase IV (DPP-IV) inhibitory activity. The stability of the in vitro biologically active BSG-PI hydrolysates to simulated gastrointestinal digestion (SGID) was determined. In addition, different peptide fractionation techniques were assessed with the goal of obtaining fractions enriched in bioactive sequences. Extraction using NaOH combined with high temperature (50 oC) and a high speed shearing pretreatment step followed by isoelectric precipitation and subsequent spraydrying resulted in a pale BSG-PI containing 52% protein. However, due to consistently low protein yield (circa 15% protein) black BSG was not further studied as a potential source of cereal protein. Polyphenol-rich co-product fractions were obtained throughout the pale and black BSG protein extraction procedures which demonstrated high antioxidant capacity. In comparison to unhydrolysed pale BSG-PI, pale BSG-PI hydrolysates demonstrated improved Nitrogen solubility between pH 2.0 to 12.0, while the apparent viscosity significantly decreased in the alkaline pH range. Pale BSG-PI exhibited good emulsion properties, particularly in the neutral to alkaline pH range, however, this improved on hydrolysis with Alcalase and Corolase PP. Pale BSG-PI and the associated hydrolysates were stable to heating at 140 oC. However, pale BSG-PI and its hydrolysates displayed poor foaming properties in the neutral to acidic pH range. The DPP-IV and ACE inhibitory potential of pale BSG-PI significantly improved on hydrolysis with commercial proteolytic preparations from different sources with the exception of papain derived hydrolysates. The Flavourzyme hydrolysate resulted in an a DPP-IV IC50 value of 2.64 mg mL-1 while the Alcalase hydrolysate exhibited an ACE IC50 of 0.32 mg mL-1 . The bioactive potential of the BSG-PI hydrolysates was retained, and in some cases increased, after SGID. Ultrafiltration (UF) resulted in improved ACE and DPP-IV IC50 values for BSG-PI hydrolysates generated using Alcalase and Flavourzyme, while semi-preparative RP-HPLC resulted in the generation of fractions with increased ACE and DPP-IV inhibitory potency. Semi-preparative RP-HPLC also demonstrated that certain peptides in the Alcalase hydrolysate may be stable to digestion by gastrointestinal enzymes. Two peptide fractions were isolated which had increased levels of both ACE and DPP-IV inhibitory activity.