Effect of soybean process by products (okara) incorporation on the quality and physicochemical properties of tofu

Okara (the insoluble portion of soymilk remaining after tofu production) has the potential to strengthen the structure of tofu. In this study, the effects of different coagulants (GDL/CaCl₂) and the okara volume ratio on tofu quality were investigated. The optimal okara additions required to increase the water holding capacity of tofu were 15 % (w/w soybean, upon acidification with glucono-δ-lactone, GDL) and 2.5 % (w/w soybean, upon electrostatic setting of proteins by CaCl₂). Under this ratio, the β-fold content of tofu increased significantly and the random curling structure decreased (p < 0.05). Crystallinity increased from 11.89 % to 13.36 % for GDL-okara tofu and from 8.08 % to 14.33 % for CaCl₂-okara tofu. Furthermore, SEM results displayed that GDL-okara tofu has a more homogeneous and dense gel network with filamentous and homogeneous pores, when compared to plain tofu. This study provided a comprehensive understanding of the gelling properties of soymilk at tofu preparation in the presence of okara under either GDL or CaCl₂, confirming that okara has the potential to improve the structure of tofu.