Effects of particle size and substitution level of brewer’s spent grain on physicochemical, nutritional, and sensory properties of cookies

Abstract Brewer’s spent grain (BSG), a major by-product of beer production, is rich in nutrients, inexpensive, and annually produced in large quantities, but is currently underutilized. In this research, the influences of particle size, i.e. coarse, medium, and fine particle size with a d4,3 value of 756.67, 561.67, and 158.33 µm, respectively, and substitution level, i.e. 10, 20, and 30% dried and ground BSG powder for wheat flour, on the physicochemical, nutritional, and sensory properties of cookies were investigated. The water and oil holding capacity of BSG powder was higher than that of wheat flour and increased with increasing particle size. The protein, fiber, ash and total phenolic content as well as the antioxidant capacity of the BSG-enriched cookies were higher than those of the control cookies and increased with increasing substitution level. The addition of BSG led to a reduction in the hardness and spread ratio of cookies, the intensity of which increased with increasing substitution level (only for hardness) and particle size of BSG. The color parameters L* and b* values decreased, while the a* value increased with increasing substitution level and decreasing particle size of BSG. The sensory evaluation showed that the acceptable substitution level of BSG increased with the reduction of particle size from 20% for coarse BSG powder to 30% for medium and fine BSG powder. The appropriate particle size is therefore a medium particle size with a substitution level of up to 30%.