Protein hydrolysates from agricultural crops have shown encouraging bioactive and techno-functional characteristics that may be used in the development of functional foods( 1 ). It is important that bioactive protein hydrolysates demonstrate an ability to retain their bioactivity during digestion. Brewers' spent grain (BSG), a by-product of the brewing industry, is a potential source for the development of protein hydrolysates. The aim of this study was to incorporate a bioactive, BSG-derived protein hydrolysate into commercially available low-fat milk and assess the cytotoxicity and immunomodulatory effects of digestates, following in vitro gastrointestinal digestion.
Hydrolysate U was obtained on Alcalase 2·4L digestion of a BSG protein-rich isolate. The hydrolysate was freeze-dried whole (U) or fractionated using 5 and 3 kDa molecular cut-off membranes, and permeates and retentate were designated U, U < 3, U < 5 and U > 5. Samples were added to low-fat milk at a concentration of 0·125% (v/v). A static gastrointestinal digestion model, as previously described( 2 ) was used to mimic human digestion. The (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) (MTT) assay was used to assess the effect of digestates (0–10% ; v/v) on Jurkat T cell proliferation. The effect of digestates on interferon-gamma (IFN-gamma) and interleukin-6 (IL-6) secretion in concanavalin-A (con-A) stimulated Jurkat T cells was measured by ELISA. Data were expressed as a percentage of untreated (control) cells.
Values are mean of three independent experiments. Statistical analysis by ANOVA followed by Dunnett's test.
* Denote significant difference in cell viability, relative to untreated Jurkat cells (P < 0·05).
Treatment with digestates of milk with added hydrolysates U, U < 3 and U < 5 at 10% (v/v) and hydrolysates U > 5 at 5% and 10% (v/v), for 24 hours significantly reduced viability of Jurkat T cells. Following on from the cytotoxicity results, the highest non-toxic concentration of digestates (2·5%) was selected for further investigation. Preliminary results suggest that milk digestates with added >5 kDa hydrolysate can decrease IFN-gamma and IL-6 secretion in stimulated Jurkat T cells (data not shown). In conclusion, these results suggest that low-fat milk fortified with BSG hydrolysate can attenuate cytokine production in stimulated Jurkat T cells.
This research was supported through the Food Institutional Research Measure, administered by the Department of Agriculture, Food and the Marine, Ireland.