Gastrointestinal digestion in vitro and technological properties of brewery residue protein isolate: effect of colloidal grinding

Abstract

Around 40 million tons of brewery spent grain (BSG), the main by-product of the brewing industry, are generated annually. This residue has a high protein content, up to 30%, and a considerable proportion of essential amino acids, including lysine, which is commonly limiting in cereal proteins. It also presents interesting technological properties, such as high emulsifying capacity. These characteristics enhance its reinsertion into the food ingredients and supplements industry as a product with high added value. However, the protein fraction of BSG, composed mainly of glutelins and prolamins, may present low digestibility, due, in part, to the complexity of the lignocellulosic matrix, which hinders the access of proteases from the gastrointestinal tract. In this context, the use of colloidal grinding, which can promote the cleavage of molecular bonds and alter the three-dimensional protein structure, is a physical method with the potential to improve the protein digestibility of foods of plant origin. The main objective of this work is to investigate the effect of colloidal grinding, in comparison with grinding in a knife mill, of BSG on the in vitro digestibility of its protein isolate obtained by alkaline extraction under different conditions. The influence of the type of grinding combined with different alkaline extraction conditions on particle size, protein solubility, water and oil retention capacity, performance as an emulsifying and foaming agent of protein isolates will also be investigated. It is expected, therefore, that the results obtained will contribute to the advancement of the reinsertion of this agro-industrial residue in the development of vegetable protein products with high digestibility for humans.