Quality and functional characteristics of tofu prepared rapidly from soybeans dried after soaking in water

In this study, Soybeans dried after soaking (SDSs) were prepared for rapid tofu production, and quality and functional characteristics of SDS‐tofu were analyzed. SDS40, SDS50, and SDS60 were prepared by soaking for 12 hr and then drying at 40, 50, and 60℃, respectively. During the soaking process in tofu production, the water absorption rate of SDSs was higher than that of control soybeans. SDS‐tofu was prepared by soaking SDSs for 1 hr. Quality, texture, and sensory characteristics were similar among tofu samples. SDS‐tofu had a higher aglycone isoflavone content (AIC) than did control tofu. SDS60‐tofu had the highest AIC, indicating high nitric oxide inhibitory effect. Antioxidant components, activities and cell viabilities were similar among control tofu and SDS‐tofu. Consequently, this study presents the possibility of enhancing efficiency of tofu production process and functionality of tofu by using SDSs because of reduction of the soaking time and the improvement of aglycone isoflavone content. NOVELTY IMPACT STATEMENT: Soybeans dried after soaking (SDSs) contained much higher contents of aglycone isoflavones than did general‐use soybeans because the former was prepared by drying soybeans at 40–60℃ after they had been completely soaked for a long time, thus allowing endogenous β‐glucosidase (optimal temperature, 60℃) to be activated, and in particular, glycitein, which was not detected in general‐use soybeans, was detected in the SDSs. The use of SDSs can shorten the moisture reabsorption time because the cross‐sectional area for moisture absorption is larger in SDSs than in general‐use soybeans, likely as the result of porous structures that form in the soybean as it dries after swelling from being soaked. By manufacturing tofu using SDSs, tofu with enhanced characteristics, can be produced quickly due to improvement of the manufacturing process, namely, the time needed for soaking is shorter, and the resulting tofu has a higher content of aglycone isoflavones from the conversion of isoflavones to aglycone isoflavones.