Use of food-grade proteases to recover umami protein-peptide mixtures from rice middlings

The effects of enzymatic hydrolysis induced by food-grade exo- plus endo-proteases (i.e. Umamizyme and Flavourzyme) on the sensory characteristics and functional properties of rice middlings were investigated. Enzymatic hydrolysis was confirmed by sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE), by monitoring the rate of hydrolysis with the Coefficient of Protein Degradation (CPD). The presence of medium-low size polypeptides at the end point of 24 h was detected, resulting from 24.84 ± 1.28 % and 67.04 ± 0.55 % hydrolysis for Flavourzyme and Umamyzyme, respectively. Sensory and functional properties, including emulsifying and foaming properties, were evaluated on hydrolysates obtained after 24 h incubation. The sensory analysis described the umami taste as the most intense attribute for all the products. These results suggest that this protocol of enzymatic hydrolysis can be used as an effective technique to produce functional protein-peptide mixture for food use leading to new added-value umami flavor enhancers from under-utilized rice middlings. The quality of the hydrolysates was also demonstrated by emulsifying and foaming properties, especially apparent in the Umamizyme-derived hydrolysates. This results proves that our method may be convenient to provide ingredients for industrial applications characterized by not only a good taste profile, but also by useful functional properties for food processing, storage and consumption.