Arii Yasuhiro
Department of Innovative Food Sciences, School of Food Sciences and Nutrition, Mukogawa Women's University, Nishinomiya, Hyogo, 663-8558, Japan.
Heliyon. 2024 Oct 16;10(20):e39319. doi: 10.1016/j.heliyon.2024.e39319. eCollection 2024 Oct 30.
Uncertainty surrounds the role of pH in tofu-like precipitate (TLP) formation using MgCl. In this study, to clarify the role of MgCl-induced pH decrease in TLP formation, the protein concentration in the supernatant, weight of wet precipitate, and the solubility in 2 M urea at constant pH (6.5 or 6.2) were measured using a buffer and comparing the buffering effect under variable pH conditions to the effect observed without buffer. Analysis of protein concentration in the supernatant showed no precipitation of soymilk proteins under stable pH conditions of 6.5. Wet precipitate formation varied substantially during TLP formation at three different pHs; the weight slightly increased with the increase in MgCl concentration up to 20 mM at a constant pH of 6.5. However, wet precipitation was substantially enhanced by MgCl (≥10 mM) at a constant pH of 6.2 but rapidly increased by MgCl (≥7 mM) under variable pH conditions. The protein concentrations and wet precipitate weight at 20 mM MgCl under constant pH conditions showed contrasting patterns. However, the weight of dry precipitate was almost the same under both constant pH (6.5 and 6.2) conditions. Urea solubility under constant and variable pH conditions differed; no urea-insoluble precipitates were produced under constant pH conditions. These results suggest that pH decrease is essential for bringing proteins closer together for MgCl-mediated TLP formation. This study will aid in understanding the mechanisms underlying TLP formation and support further discovery of new coagulants for the effective production of new tofu-like and tofu-based foods.
使用氯化镁（MgCl）形成豆腐状沉淀（TLP）时，pH值所起的作用尚不确定。在本研究中，为了阐明MgCl诱导的pH值降低在TLP形成中的作用，使用缓冲液测量了上清液中的蛋白质浓度、湿沉淀的重量以及在恒定pH值（6.5或6.2）下在2M尿素中的溶解度，并将可变pH条件下的缓冲效果与无缓冲液时观察到的效果进行比较。上清液中蛋白质浓度的分析表明，在稳定的pH值6.5条件下，豆浆蛋白没有沉淀。在三种不同pH值的TLP形成过程中，湿沉淀的形成有很大差异；在恒定pH值6.5下，随着MgCl浓度增加至20mM，重量略有增加。然而，在恒定pH值6.2时，MgCl（≥10mM）可显著增强湿沉淀，但在可变pH条件下，MgCl（≥7mM）可使湿沉淀迅速增加。在恒定pH条件下，20mM MgCl时的蛋白质浓度和湿沉淀重量呈现出相反的模式。然而，在恒定pH（6.5和6.2）条件下，干沉淀的重量几乎相同。恒定和可变pH条件下的尿素溶解度不同；在恒定pH条件下未产生尿素不溶性沉淀。这些结果表明，pH值降低对于使蛋白质更紧密聚集以实现MgCl介导的TLP形成至关重要。本研究将有助于理解TLP形成的潜在机制，并支持进一步发现用于有效生产新型豆腐状和豆腐基食品的新型凝固剂。
