# Effects of Organic Acid Coagulants on the Textural and Physical-Chemical Properties of Tofu
## 3 Results and Discussion
### Texture Profile Analysis (TPA)
In a study in which defatted soybean meal was added to the tofu to improve its physical properties by applying the coagulant magnesium chloride and 0.5% glucono delta lactone (GDL), the texture profile of white tofu (without adding defatted soybean meal) was evaluated with TPA in cubic samples of a 2-cm diameter by applying 50% compression and speed of 2.00 mm/s, which obtained the following results: a hardness of 0.52 N, a cohesiveness of 0.60, an adhesiveness of 0.31 g/cm, and an elasticity of 0.40 [16]. Meanwhile, another study evaluated the technological and sensorial properties of a tofu-similar product by applying milk whey to the soybean extract and using the coagulant lactic acid and 0.5% glucono delta lactone (GDL), in which the texture profile was studied by performing TPA on cubic samples of 1 cm diameter, a speed of 1.0 mm/s, and a compression of 75% [17]. They obtained the following results: a hardness of 2.52 N, a cohesiveness of 0.58, an adhesiveness of 1.47 g/cm, and an elasticity of 0.44. Thus, the results reached in this research do not coincide with any cited author; this is because the above-cited authors applied glucono delta lactone (GDL) in their research, and this coagulant has an incidence on textural properties. As mentioned, glucono delta lactone (GDL) was used as an acidity regulator, providing a gradual decrease in the pH, which caused very slow acidification, and thus no flocculation of proteins occurred (as with strong acids); on the contrary, protein gelification was produced, thus obtaining products of soft but fragile textures in the form of gels [25]. Therefore, comparing the obtained results with the ones obtained by the authors mentioned above, it is possible to indicate that the tofu from this research showed different textural properties; that is, the tofu samples with higher hardness values were less cohesive and more adhesive, while the least hard ones showed higher cohesiveness and lower adhesiveness, thus proving that the tofu obtained by using different kinds of vinegar as coagulants had excellent textural properties. These findings can be explained because, within the evaluated matrix for the set-up of the treatments, when applying the coagulant, pH values from 4.7 to 5.0 were managed upon coagulation, as well as applying high temperatures for cooking the soymik. Then, it was reduced to begin the coagulation process, thus utilizing the textural properties of the reserve globulins (7S and 11S), preserving the proteins in the soybean. The protein content played a crucial role in determining the texture of the tofu, mainly when different types of vinegar were used as coagulants. The most critical proteins in soybean are reserve globulins 7S (\(\beta\)-congylcin) and 11S (glycinin), with a quaternary structure, which has a high presence of amino acids, such as lysine, leucine, and isoleucine; these proteins are essential in forming the tofu's structure and precipitate at pH from 4.5 to 4.8. These proteins denature and aggregate upon heating, forming a gel that dictates the tofu's textural properties [26]. The 11S/7S ratio is particularly significant, with higher ratios contributing to the increased hardness, elasticity, and chewability of tofu [27]. Another study mentions that, independently from the coagulant types used, everything depends on the protein subunits of group IIb, which play an essential role in contributing to the tofu firmness. In contrast, the subunit of group IIa negatively affects the hardness and firmness of the tofu [27]. Additionally, it is mentioned that such proteins show SH (thiol) groups and SS (disulfide) bonds, which influence their properties (gelification, adhesion, cohesion, and elasticity); these properties are influenced by the pH, temperature warming, and cooling speed. When using different types of vinegar, the acidic environment affects the protein structure and interactions. Vinegar with lower pH values, such as apple vinegar, can enhance the denaturation and aggregation of proteins, resulting in firmer and more elastic tofu.