NaCl浓度和pH对甘薯蛋白肽乳化特性的影响

【目的】明确不同NaCl浓度和pH对甘薯蛋白肽乳化特性的影响，为甘薯蛋白肽在食品工业中的应用提供理论依据。【方法】测定不同NaCl浓度（0.2、0.4、0.6、0.8和1.0 mol·L^-1）和不同pH（3、5、7和9）条件下，甘薯蛋白肽乳化液的显微结构、乳化颗粒平均粒径（d_4,3）、乳化活性、乳化稳定性、流变学性质和甘薯蛋白肽的表面疏水活性。【结果】与未添加NaCl的相比，添加浓度为0.2 mol·L^-1的NaCl时，甘薯蛋白肽乳化液的d_4,3由54.19 μm增大至59.70 μm；乳化活性指数由86.29 m²·g^-1显著降低为56.35 m²·g^-1（P＜0.05）；乳化稳定性指数由14.84 min降为13.19 min。然而，随着NaCl浓度的增大，甘薯蛋白肽乳化颗粒均一程度降低，d_4,3进一步由0.2 mol·L^-1时的59.70 μm增加至69.72 μm；而乳化活性由56.35 m²·g^-1逐渐降低至32.32 m²·g^-1，乳化稳定性呈先升高后降低的趋势，在0.4 m²·g^-1时达最大值，为15.55 min；初始表观黏度增大，并有剪切变稀现象发生；表面疏水活性降低。此外，随着pH增加，乳化颗粒均一程度升高，d_4,3由pH 3时的64.45 μm减小至pH 9时的51.21 μm；而乳化活性由pH 3时的3.99 m²·g^-1升高至pH 9时的120.47 m²·g^-1，乳化稳定性呈先降低后升高的变化趋势，pH 3时其最佳值为29.13 min；初始表观黏度降低，并有剪切变稀现象发生；表面疏水活性升高。【结论】甘薯蛋白肽的乳化特性与NaCl浓度和pH密切相关，添加≥0.2 mol·L^-1 NaCl降低了甘薯蛋白肽的乳化活性和稳定性，而增加pH可有效提高甘薯蛋白肽的乳化活性。

Effects of NaCl Concentration and pH Value on the Emulsifying Properties of Sweet Potato Peptides

【Objective】 The study aims to clear the effects of different NaCl concentrations and pH values on the emulsifying properties of sweet potato peptides and provide a theoretical basis for the application of sweet potato peptides in the food industry. 【Method】Microstructure, average particle size (d_4,3), emulsifying activity, emulsifying stability, rheological property of emulsion and hydrophobicity of sweet potato peptides with different NaCl concentrations (0.2, 0.4, 0.6, 0.8 and 1.0 mol·L^-1) and different pH values (3, 5, 7 and 9) were measured. 【Result】Compared with the sweet potato peptide emulsion without NaCl, when 0.2 mol·L^-1 NaCl was added into the sweet potato peptide emulsion, d_4,3 was increased from 54.19 μm to 59.70 μm, the emulsifying activity index was decreased significantly from 86.29 m²·g^-1 to 56.35 m²·g^-1 (P＜0.05), and the emulsion stability index was decreased from 14.84 min to 13.19 min. However, with the increase of NaCl concentration, the uniformity of sweet potato peptide emulsion was decreased, d_4,3 was further increased from 59.70 μm to 69.72 μm, the emulsifying activity was decreased from 56.35 m²·g^-1 to 32.32 m²·g^-1, emulsifying stability was firstly increased and then decreased, reached a maximum of 15.55 min at 0.04 mol·L^-1, the initial apparent viscosity was increased and exhibited shear-thinning phenomenon, and surface hydrophobicity activity was decreased. In addition, with the increase of pH value, the uniformity of emulsion was increased, d_4,3 was decreased from 64.45 μm at pH 3 to 51.21 μm at pH 9, the emulsifying activity was increased from 3.99 m²·g^-1 at pH 3 to 120.47 m²·g^-1 at pH 9, the emulsifying stability was firstly increased and then decreased, reached a maximum of 29.13 min at pH 3, initial apparent viscosity was reduced and exhibited shear-thinning phenomenon, and the activity of surface hydrophobicity was increased. 【Conclusion】 Emulsifying properties of sweet potato peptides are closely related to the NaCl concentration and pH value. Addition of NaCl (≥0.2 mol·L^-1) reduced the emulsifying activity and stability of sweet potato peptides, while the increase of pH value could effectively improve the emulsifying activity of sweet potato peptides.