Abstract: In this research, three different methods namely cooking soybean slurry before filtration, cooking soybean milk after filtration of soybean slurry to remove okara and adding hot water into soybean slurry with stirring before filtration were compared in terms of tofu yield and water retention to find the best one to produce northern Chinese tofu. Furthermore, the effects of soybean-to-water ratio for grounding, curding temperature, MgCl2 dosage and curding time on the quality characteristics of tofu were examined and tofu yield and water retention were correlated with texture properties of tofu. The results showed that tofu yield and water retention obtained from the second method were significantly higher than those obtained from the other two. The optimized conditions that provided maximum tofu yield and water retention were determined as follows: soybean-to-water ratio for grounding, 1:7 (g/mL); curding temperature, 80 ℃, 0.6 mol/L MgCl2 dosage, 18 mL/L; and curding time, 20 min. The correlation analysis showed that under different processing conditions, tofu yield and water retention were correlated negatively with hardness, cohesiveness and resilience but positively with chewiness, gumminess and flexibility.

Key words: northern Chinese tofu, tofu yield, water retention, processing, texture characteristics