Effect of different protein isolates and transglutaminase on rice flour properties

The effect of the addition of different protein isolates (pea, soybean, egg albumen and whey proteins) on the viscosimetric and rheological properties of the rice flour dough, and the development of a protein network through the use of microbial transglutaminase (TG) were evaluated. Protein isolates significantly (p < 0.05) modified the gelatinization and gelling behaviour of the rice starch determined in the rapid viscoanalyser (RVA). Pea, soybean and whey proteins significantly (p < 0.05) decreased the final viscosity in addition, whey protein also promoted a significant decrease (27.3%) in the peak viscosity. The elastic modulus value (G') recorded in the oscillatory tests was significantly (p < 0.01) affected by both the protein isolates and the TG. The extent of the effect was dependent on the protein source; pea and soybean increased this parameter, whereas egg albumen and whey protein drastically decreased it. A modification in the emulsifying properties was also observed by the addition of protein isolates and the TG treatment. The decrease in the amount of free amino groups after TG treatment confirmed the protein crosslinking catalysed by TG. Therefore, the use of protein isolates and TG broads the applications of rice flour in the bakery industry, and brings about an increase in the protein content with the subsequent nutritional improvement of the resulting products. (C) 2007 Elsevier Ltd. All rights reserved.