Preparation, characterization, nanostructures and bio functional analysis of sonicated protein co-precipitates from brewers' spent grain and soybean flour

•Sonication decrease the protein content in protein co-precipitates.•Sonicated protein co-precipitates had microstructure with aggregates and nanometer particles.•Decreased levels of free and bound phenolics from sonicated protein co-precipitates.•Bound phenolics of sonicated protein co-precipitates decreased antioxidant and ACE activities.•Phenolics from sonicated protein co-precipitates improved α-amylase inhibitory activity.

This investigation was performed to assess the effects of sonication on the structure of protein, extractability of phenolics, and biological properties of isolated proteins and protein co-precipitates prepared from brewers' spent grain and soybean flour. Scanning electron micrographs revealed that the sonicated protein isolates and co-precipitates had different microstructures with fewer aggregates and smaller particles down to the nanometer scale compared to non-sonicated samples. However, the levels of free and bound phenolics extracted from non-sonicated protein isolates and protein co-precipitates increased compared to sonicated samples. The bound phenolics extracted after acid hydrolysis of sonicated protein co-precipitates showed improved ACE inhibitory activity and diminished antioxidant potency compared to non-sonicated samples. However, the free phenolics extracted from sonicated protein co-precipitates showed decreased ACE inhibitory activity and increased antioxidant activities compared to non-sonicated samples. The free and bound phenolics extracted from sonicated protein co-precipitates showed increased alpha-amylase inhibitory activity compared to non-sonicated samples.