Impact of heat treatment on the acid induced gelation of brewers’ spent grain protein isolate

Abstract

Brewers’ spent grain (BSG) is a major side stream of the beer-brewing sector, which comprises a plethora of food macromolecules and micronutrients. In the present work, BSG protein isolates were assessed for their ability to form gels via delta-gluconolactone induced acidification. The impact of the thermal pre-treatment (native, heating at 72, 85 or 92 °C for 20 min, or autoclaving) of the BSG-PI dispersions (5% w/w) on the acid-induced gelation kinetics and the microstructural, rheological and water holding capacity characteristics of the acid gels was investigated. The gelation lag phase and the maximal gelation rate values were reduced proportionally to the intensity of the heat treatment allowing a better-controlled aggregation of the protein protofibrils into clusters, which in turn resulted in a percolated network formed by the protein clusters supramolecular interactions. The thermal treatment of the BSG-PI dispersions favoured the occurrence of segregative phase separation between glutelins and alkali-soluble cell wall dietary fibres. The arrestment of the segregative phase separation during the acidification process resulted in the development of composite acid gels of enhanced elasticity, stiffness and deformation resilience. All gel systems had high water holding capacity (>86%), which postulates the occurrence of covalent (disulphide bonds) interactions between the protein inter-flocs.