Cellular in vitro bioactivity of protein hydrolysates from brewers' spent grain

Abstract

Protein hydrolysates have been used as components of nutrition products, including geriatric and sports products, and in weight-control diets(1). Brewers' spent grain (BSG), a co-product of the brewing industry, represents a unique source of protein hydrolysates. The aim of this study was to assess the in vitro bioactivity of BSG hydrolysates and fractionated hydrolysates. Hydrolysates (designated U-W) were prepared from BSG using either Alcalase 2.4L, Corolase PP or Flavourzyme. Cytotoxicity was measured using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay in both U937 and Jurkat T cells. The antioxidant activity of the hydrolysates was determined in U937 cells by two methods - ability to protect against hydrogen peroxide (H2O2)-induced (100 muM 60 min) oxidative stress, by the SOD assay and H2O2-induced (50 muMx30 min) DNA damage, by the comet assay. An enzyme-linked immunosorbent assay (ELISA) was used to measure the effect of the samples on concanavalin-A (con-A) stimulated production of interferon-gamma (IFN-gamma) in Jurkat T cells, indicating their immunomodulatory potential. (Table presented) BSG protein hydrolysates were more cytotoxic in U937 than in Jurkat T cells (data not shown). Addition of H2O2 to U937 cells decreased SOD activity to 57.2% and increased % tail DNA to approximately 41.8% (P<0.05). Lowest molecular weight (m.w.) hydrolysates (<3,<5 kDa) showed strong protection against SOD reduction (P<0.01), particularly for fractionated hydrolysates of U and W. Only W<5 kDa significantly (P<0.01) repaired H2O2-induced DNA damage. Contrastingly, unfractionated hydrolysates and hydrolysates with higher m.w. (>5 kDa) possessed significant (P<0.05) anti-inflammatory potential, reducing IFN-gamma production by up to 22.3%. In conclusion, this study suggests BSG protein hydrolysates have bioactive potential; with low m.w. and higher m.w. fractionated hydrolysates demonstrating antioxidant and anti-inflammatory effects, respectively. These hydrolysates represent novel bioactive ingredients for inclusion in functional foods.