Emulsifying and emulsion-stabilizing properties of gluten hydrolysates

Gluten is produced as a coproduct of the wheat starch isolation process. In this study, gluten was hydrolyzed to degrees of hydrolysis (DH) of 3-6-10 and 1-2-3 with alcalase and trypsin, respectively. These peptidases have a clearly distinct substrate specificity. Corn oil-in-water emulsions (10 wt % oil) were prepared by high-pressure homogenization at pH 7.5. Gluten peptides with DH 3 proved to be the most effective in producing peptides displaying emulsifying properties. Higher levels of alcalase hydrolysates (2.0 wt %) than of trypsin hydrolysates (1.0 wt %) were required to produce stable emulsions with small droplet sizes, which is attributed to differences in the nature of the peptides formed. The emulsions had small mean droplet diameters (d32 < 1000 nm). Emulsions produced with trypsin hydrolysates (stable after 9 days at 55 °C) displayed better thermal stability compared to those produced with alcalase hydrolysates (destabilized after 2 days at 37 °C). The hydrolysate-containing emulsions, however, were quickly destabilized by salt addition (≤100 mM NaCl) and when the pH approached the isoelectric point of the coated droplets (pH ~5.5). Microscopic analysis revealed the formation of air-in-oil-in-water emulsions at lower hydrolysate concentrations, whereas at higher concentrations (≥3.0 wt %) extensive flocculation occurred. Both phenomena contributed to creaming of the emulsions. These results may be useful for the utilization of gluten hydrolysates in food and beverage products.