Mass balance study of isoflavones during soybean processing

The effects of processing techniques on the distribution of isoflavones were investigated by manufacturing tempeh, soymilk, tofu, and protein isolate. The manufacturing steps causing significant losses (p < 0.05) of isoflavones were as follows: soaking (12%) and heat processing (49%) in tempeh production; coagulation (44%) in tofu processing; and alkaline extraction (53%) in soy protein isolate production. In the production of tempeh, soymilk, and tofu, malonyldaidzin and malonylgenistin decreased after soaking and cooking. Concomitantly, acetyldaidzin and acetyl-genistin were generated during heat processing. After fermentation, daidzein and genistein concentrations increased in tempeh, apparently as a result of fungal enzymatic hydrolysis. In protein isolate processing, alkaline extraction caused the generation of daidzein and genistein, probably through alkaline hydrolysis.