Texture evaluation of tofu (soybean curd) by viscoelastic tests

摘要

Viscoelastic tests (stress-strain and stress relaxation tests) were applied to evaluate the texture of tofu. Tofu was made in the laboratory by using different concentrations of soymilk (5%, 6%, 7%, 8% and 9%, w/v) and coagulants, such as glucono-delta-lactone (GDL) and calcium sulfate. The parameters of stress-strain behaviors of GDL-coagulated tofu were higher than that of CaSO{sub}4-coagulated tofu at the same soymilk concentration. A 4-element model, composed of 2 Maxwell models, was conformed to fit the stress relaxation curves. The elastic parameters E{sub}1, E{sub}2 for the 4-element model did not significantly change while viscous parameters η{sub}1, η{sub}2 and relaxation time τ{sub}1, τ{sub}2 increased with increasing soymilk concentration. Viscoelastic behaviors of tofu suggested the stronger structures accompanying with the increase of soymilk concentration. It seemed that the stress-strain behavior was involved more with the viscous parameters than the elastic ones. These results showed that viscoelastic tests were effective for texture evaluation of tofu. Using this method, the commercial tofu in a local market of China was analyzed. The results showed that very hard tofu was being distributed in the market of China and it was possible to produce tofu by the production method of kinugoshi tofu (no press tofu) with a texture similar to the commercial tofu in China when using CaSO{sub}4 as a coagulant.