In general, the higher the content of the protein particle, the fasterthe soymilk coagulates in response to calcium ions and theharder the final gel is. However, the rapid coagulation processhas an adverse effect on the formation of fine gel networks, therebyresulting in the decrease in yields (Guo & Ono, 2005; Li, Cheng,Tatsumi, Saito, & Yin, 2014). Results showed that by applying HTPCtreatment during soymilk preparation, the yield increased and abetter texture of the resulting tofu product was obtained. Thus,the coagulation process of the whole soymilk, particulate proteins,and non-particulate proteins was analyzed with the addition ofCa2+. The results are shown in Fig. 3. The protein solubility of TCsoymilk decreased when the concentration of Ca2+ reached4 mM. Nearly all proteins were precipitated when the concentrationof Ca2+ was 10 mM. Compared with the TC soymilk, the onsetof protein precipitation in HTPC soymilk occurred later, whichrequired the concentration of Ca2 to reach 6 mM. The final concentrationof Ca2+ that allowed protein precipitation was even higher(12 mM, as shown in Fig. 3A). The above-mentioned results suggestthat the HTPC process on soymilk lowers the sensitivity of soymilkproteins in response to Ca2+ and forms more protein particles. Arelatively low sensitivity to Ca2+ reportedly contributes to sufficientinteraction among soymilk proteins and that the obtainedgel network is denser and more homogeneous (Obatolu, 2008;Prabhakaran, Perera, & Valiyaveettil, 2006).Thus, the lowsensitivity of protein in response to Ca2+ may possibly explainthe high yield and the water and solid contents of the tofu preparedfrom HTPC soymilk.Phytic acids of soymilk affect the coagulation process during theproduction of tofu. With increasing phytic acid content, the onsetof soymilk coagulation occurs at a higher concentration of Ca2+,and the optimum concentration of Ca2+ used for the productionof tofu also increases. As a result, the whole coagulation processbecomes quite slow (Ishiguro, Ono, & Nakasato, 2008; Wanget al., 2015). In this study, the same soybean variety was utilized,and the total phytic acid content of the soymilks was3.07 ± 0.27 mM. Regardless of the cooking process, the proportionsof free phytic acid in HTPC and TC soymilks were similar and comprised52% of the total phytic acid content. It suggests that theHTPC treatment on soymilk does not alter the protein-phytic acidinteraction. The difference of the two soymilks in the coagulationprocess is consequently not affected by the variation in the levelof free phytic acids.The Ca2+-induced coagulation of particulate and non-particulateprotein fractions was analyzed (shown in Fig. 3B). Compared withthe non-particulate protein fraction, particulate proteins exhibitedhigher sensitivity to Ca2+. Regardless of the cooking method, theCa2+-induced coagulation process was similar, where the proteinsolubility began to lose at the Ca2+ concentration of 2 mM, thendrastically decreased with the addition of Ca2+, and reached theminimum at the Ca2+ concentration of 6 mM. This result is inaccordance with previous studies (Guo et al., 1999; Ono et al.,1993). Although both exhibited a low sensitivity to Ca2+, the nonparticulateproteins fractionated from HTPC soymilk had an evenlower sensitivity to Ca2+ than that from TC soymilk; thus, thedecrease in its protein solubility occurred and reached maximumlevel at high Ca2+ levels. In summary, the hysteresis of proteincoagulation occurs