In vitro antioxidant and anti-inflammatory effects of brewers' spent grain protein rich isolate and its associated hydrolysates

Brewers' spent grain (BSG) is a protein-rich by-product of the brewing industry. The present study examined the in vitro bioactivity of a BSG protein enriched preparation and its associated enzymatic hydrolysates (assigned A-J). Cytotoxicity was measured using the (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) MTT assay in U937 and Jurkat T cells. IC₅₀ values were lower in the U937 cell line, ranging from 4.93 to 9.27% v/v versus a range of 4.11% v/v to undetectable in Jurkat T cells. The superoxide dismutase (SOD) and comet assays were performed on U937 cells pre-incubated with test samples and subsequently exposed to an oxidant. Hydrogen peroxide (H₂O₂) significantly reduced SOD activity by 37.7% and none of the test samples provided protection. None of the samples protected against DNA damage induced by tert-butylhydroperoxide (t-BOOH); hydrolysate H, prepared with Alcalase at 60°C, protected against H₂O₂-induced DNA damage. The total phenolic content (TPC) was found to range from 0.021 to 0.055mg GAE/mg dry powder. The effect of the BSG-derived test samples on cytokine production (IL-2, IL-4, IL-10, IFN-γ) in Concanavalin A (conA) stimulated Jurkat T cells was measured using an enzyme linked immunosorbent assay (ELISA). The samples had no effect on IL-2 and IL-4 production. The unhydrolysed sample C significantly reduced IL-10, while the protein rich isolate, unhydrolysed control samples and hydrolysates D, E, F, and J significantly reduced IFN-γ production. The BSG preparations possess little antioxidant potential and exhibit selective immunomodulatory effects that may be of benefit in the control of inflammatory diseases.