Nutritional and Techno-Functional Characterisation of Brewers’ Spent Grain and Legume Proteins for Blended Protein Systems in Plant-Based Yoghurt Alternatives

Abstract

Brewers’ spent grain (BSG) is a brewing by-product with potential as a sustainable protein source. However, its limited amino acid profile and weak gelation properties limit its use in plant-based yoghurt alternatives (YAs). This study evaluated the compositional and techno-functional properties of brewers’ spent grain protein isolate (BSGI), pea protein isolate (PPI), mung bean protein isolate (MBP), and chickpea protein concentrate (CPC), and investigated their suitability in fermented YAs. BSGI was deficient in lysine, while PPI and MBP were limited in sulfur amino acids, highlighting the potential nutritional complementarity of cereal-legume protein blends. BSGI was blended with each legume ingredient at a fixed 50:50 ratio and fermented to a pH of 4.5 using a Streptococcus thermophilus culture. All YAs contained over 3.0% protein and showed improved indispensable amino acid profiles. The BSGI + MBP blend demonstrated the highest water retention, firmness, consistency, and rheological strength, followed by BSGI + PPI, whereas BSGI + CPC had the weakest gel structure. These formulation-level differences cannot be attributed solely to the intrinsic functionality of the individual protein ingredients, as protein content and non-protein components, particularly dietary fibre, differed among formulations. Overall, BSGI shows potential for incorporation into mixed plant-protein YAs and supports further optimisation of sustainable cereal-legume protein systems.