39C-2

Z. Y. JU and N. S. HETTIARACHCHY. Department of Food Science, University of Arkansas, Fayetteville, AR 72704

Isoflavones in soybean have attracted interest because of their biological activities and potential health benefits. Over 15-million Americans consume tofu, hence tofu is a suitable vehicle to deliver isoflavones. Approximately 60% isoflavones are lost in soy whey, okara or soaking solution during tofu production.

The purpose of this study was to investigate the retention of isoflavones in tofu by incorporating selected proteins during tofu preparation.

Control tofu was prepared by soaking whole soybean (50 g) in water (1:2.7,w/v) for 10 hours and grinding with distilled water (1:3 w/v). Filtrate from the slurry (soymilk) was boiled, cooled to 80^oC and coagulant (0.2% CaSO₄.1/2 H₂O) added. The curd (tofu) formed at 80^oC for 20 min was pressed to drain whey. To enhance the retention of isoflavones in tofu, 4% casein /whey protein isolate (WPI) /Rice protein isolate (RPI) /gluten (optimum amount) were incorporated during grinding step of tofu preparation. The isoflavones contents in soybean, tofu, whey, okara and soaking solution were determined by reverse-phase HPLC. Textural properties were determined by Texture Analyzer.

Tofu yields with additions of casein, WPI, RPI and gluten were 154, 155, 158 and 127g respectively (123g, control). Control tofu, okara, soy whey and soaking solution contained 38.0, 21.4, 39.1 and 1.4% of total soybean genistin+genistein (97.6mg), and 45.0, 13.2, 35.8 and 6.0% of total soybean daidzin+daidzein (15.1mg), respectively. An increase in retention of genistin+genistein (64.0%, 64.4% & 42.8%) and daidzin+daidzein (51.7%, 71.5% & 55.6%) in tofu was observed upon additions of casein, WPI and RPI. Gluten addition had very little effect on the retention of the isoflavones. WPI /casein incorporated tofu had significant improvement in textural properties (hardness, cohesiveness, springiness, gumminess and chewiness) (P < 0.05).

The data suggest that WPI and casein can be used in tofu manufacturing to improve isoflavone retention and textural properties.