Effects of organic acid coagulants on the physical properties of and chemical interactions in tofu

- Acidification rate during coagulation critically impacts tofu quality.
- Gentler acidification promotes hydrophobic interactions.
- Stronger hydrophobic interactions increase non-freezable water content.
- Stronger hydrophobic interactions also improve tofu texture.
- Stronger protein-protein interactions generate a more compact tofu microstructure.

To improve tofu quality, the effects of using 0.12-0.18 g/100 mL citric acid, l-(-)-malic acid, or tartaric acid as coagulation agents were investigated. The results showed that storage modulus, hardness, water-holding capacity, non-freezable water content, and in-gel hydrophobic interactions were optimal when tofu was prepared with 0.14 g/100 mL organic acids, but deteriorated when more than 0.16 g/100 mL was used. Slower acidification during gelling in the presence of 0.14 g/100 mL organic acid promoted protein-protein hydrophobic interactions, resulting in a higher elastic modulus. Moreover, the tofu products showed higher water-holding capacity and non-freezable water content, as well as more compact gel microstructures. Notably, tofu prepared with citric or l-(-)-malic acid was of better quality than tofu prepared with tartaric acid. Collectively, the results demonstrate that soft or firm tofu with desirable physicochemical properties can be prepared with organic acids if acidification is adequately controlled during gelation.