Potential of brewers' spent grain in yogurt fermentation and evaluation of its impact in rheological behaviour, consistency, microstructural properties and acidity profile during the refrigerated storage

Abstract

Brewers' spent grain (BSG) contains high amounts of dietary fiber, which may regulate the food matrix behaviour. The study aimed to evaluate the impact of spent grain on yogurt. Different levels of BSG were substituted in yogurt fermentation and its impacts on microstructural properties including surface chemical properties and confocal microstructures were studied. The quality of the yogurt was evaluated by determining rheological behavior, syneresis, color, acidity and the amount of lactic acid bacteria (LAB) at 1, 7 and 14 days of storage. The addition of BSG shortened the fermentation time, increased the viscosity and shear stress. FTIR analysis showed that BSG intensifies the band region stretching which describes a modification in a certain functional group. Confocal laser scanning microscopy identified a disruption in the cross-link between fat-protein and yogurt matrix due to the addition of BSG. During the storage, BSG was able to maintain the flow behaviour and stability, which was shown as the change in flow behaviour and syneresis. Furthermore, BSG provided the nutrients for the survival of LAB during the storage and maintained the amount of lactic acid in yogurt during the 14 days of refrigerated storage. The substitution 5%-10% of BSG improved the quality of yogurt as the maximum quality such as acidity, rheological behavior and LAB growth. Even though 15%-20% of BSG generated the same level of acidity and LAB, and had the lowest syneresis, it diminished the flow performance of the yogurt.