Teagasc Food Research Centre, Food Chemistry & Technology Department, Moorepark, Fermoy, P61 C996 Cork, Ireland.
School of Food and Nutritional Sciences, University College Cork, T12 YT20 Cork, Ireland.
Molecules. 2021 May 19;26(10):3015. doi: 10.3390/molecules26103015.
Soy protein isolate (SPI) powders often have poor water solubility, particularly at pH values close to neutral, which is an attribute that is an issue for its incorporation into complex nutritional systems. Therefore, the objective of this study was to improve SPI solubility while maintaining low viscosity. Thus, the intention was to examine the solubility and rheological properties of a commercial SPI powder at pH values of 2.0, 6.9, and 9.0, and determine if heat treatment at acidic or alkaline conditions might positively influence protein solubility, once re-adjusted back to pH 6.9. Adjusting the pH of SPI dispersions from pH 6.9 to 2.0 or 9.0 led to an increase in protein solubility with a concomitant increase in viscosity at 20 °C. Meanwhile, heat treatment at 90 °C significantly improved the solubility at all pH values and resulted in a decrease in viscosity in samples heated at pH 9.0. All SPI dispersions measured under low-amplitude rheological conditions showed elastic-like behaviour (i.e., ' > ″), indicating a weak "gel-like" structure at frequencies less than 10 Hz. In summary, the physical properties of SPI can be manipulated through heat treatment under acidic or alkaline conditions when the protein subunits are dissociated, before re-adjusting to pH 6.9.
大豆分离蛋白（SPI）粉末通常水溶性较差，尤其是在接近中性 pH 值的条件下，这一特性使其在复杂营养体系中的应用受到限制。因此，本研究旨在提高 SPI 的溶解度，同时保持低黏度。为此，研究人员检测了在 pH 值为 2.0、6.9 和 9.0 条件下，商业 SPI 粉末的溶解度和流变性能，并确定在酸性或碱性条件下进行热处理后，能否在重新调整至 pH 值 6.9 时，对蛋白质溶解度产生积极影响。将 SPI 分散体的 pH 值从 6.9 调节至 2.0 或 9.0 会导致蛋白质溶解度增加，同时在 20°C 时黏度也会增加。而在 90°C 下进行热处理则能显著提高所有 pH 值下的溶解度，并降低在 pH 值为 9.0 下加热的样品的黏度。在低幅度流变条件下测量的所有 SPI 分散体均表现出弹性行为（即“ > ″），这表明在低于 10 Hz 的频率下存在较弱的“凝胶状”结构。综上所述，通过在酸性或碱性条件下对 SPI 进行热处理，使蛋白质亚基解离，然后再将其调整至 pH 值 6.9，可以改变 SPI 的物理性质。
