等电点附近的大豆蛋白由于所带电荷减少、疏水相互作用增强而以聚集体的形式存在且其溶解性较差，故鲜有研究者关注该条件下大豆蛋白的乳化特性。本研究从颗粒稳定乳液的角度出发，分别以等电点附近（pH 5.0）和远离等电点（pH 7.0）两个条件制备了大豆分离蛋白（soy protein isolate，SPI）稳定的乳液，比较了两种条件下SPI的界面性质及所得乳液的储藏稳定性。结果发现，pH 5.0时SPI的溶解度仅为4.70±0.15%，远远低于pH 7.0时的93.28±1.89%；然而SPI浓度为0.50%时，pH 5.0的界面压却高于pH 7.0；以pH 5.0条件制备的SPI乳液，其界面蛋白吸附量高达87.03±1.28%，而pH 7.0制备的乳液仅为36.15±1.48%；pH 5.0的乳液两个月后液滴的平均粒径为63.15±0.30 μm，与新鲜制备乳液（62.36±0.41 μm）相比基本不变；pH 7.0的乳液经过两个月储藏后其液滴平均粒径从45.78±0.38 μm增加至55.19±1.86 μm。可见，以等电点附近条件制备的SPI乳液依然具有良好的储藏稳定性。

At pH near the isoelectric point (pI), soy protein exhibits reduced electric charge and enhanced hydrophobic interactions, causing aggregation that results in poor solubility. Therefore, the emulsifying properties of soy protein under these conditions have received little attention. In this study, a soy protein isolate (SPI) was used to prepare stable emulsions at pH 5.0, which was near the pI, and pH 7.0, which was far from the pI. Soy protein aggregate particles were used to stabilize the emulsion. The interfacial properties of SPI under such conditions and the storage stability of the resulting emulsions were investigated. The results indicated that the solubility of SPI was 4.70 ± 0.15% at pH 5.0, which was much lower than that at pH 7.0 (93.28 ± 1.89%). At a concentration of 0.5% SPI, higher surface tension was observed at pH 5.0 when compared with that at pH 7.0. Moreover, the surface protein adsorption capacity of the emulsion prepared at pH 5.0 was 87.04 ± 1.28%, which was significantly higher than that prepared at pH 7.0 (36.15 ± 1.48%). After two months of storage, the average size of the droplets in the emulsion prepared at pH 5.0 was 63.15 ± 0.30 μm, which was similar to that of the droplets in freshly prepared emulsion (62.36 ± 0.41 μm). In the case of the emulsion prepared at pH 7.0, the average size of the droplets increased from 45.78 ± 0.38 to 55.19 ± 1.86 μm after storage for two months. Thus, we conclude that SPI prepared at pH near its isoelectric point can be used as an efficient emulsifier.

中国博士后科学基金一等资助（2013M530367）；中国博士后科学基金特别资助（2014T70811）；“十二五”国家科技支撑计划项目（2012BAD33B10）和国家自然科学基金面上项目（31371744）