大豆蛋白部分替代牛乳蛋白对酸奶理化性质及结构的影响

Effect of partial replacement of milk protein by soy protein on the physicochemical properties and structure of yogurt

用大豆蛋白(soy protein isolate,SPI)部分替代奶粉中的牛乳蛋白制备酸奶,通过对酸奶的理化性质(pH值、滴定酸度、持水力、色差)、质构特性等指标的测定,探究其对酸奶性质的影响,并通过测定电位、粒径、疏水性、微观结构及蛋白质二级结构,探究其对酸奶内部结构的影响。实验结果表明,随SPI替代量的增加(0%~50%),改善了酸奶感官品质,增强了其结构性质;酸奶滴定酸度降低了17.66°T(P<0.05)、持水力提高到59.17%(P<0.05)、质构特性均有所增强(P<0.05)、粒径与电位显著增大(P<0.05)。在物理结构上,随SPI替代量的增大,酸奶中2种蛋白相互交联形成了致密的网络凝乳,替代量30%时优于传统酸奶凝乳,替代量50%时更接近豆腐凝乳。在化学结构上随着SPI替代量的增加,β-折叠的含量有下降的趋势,相对的α-螺旋、β-转角、无规卷曲有不同程度的增加;SPI的加入明显增强酸奶的理化性质及凝乳结构且30%为最佳替代量。

The yogurt was prepared by partially replacing cow milk protein in milk powder with soy protein isolate(SPI).The influence of substitution of SPI for milk protein on the properties of yogurt was investigated by measuring the physicochemical properties(pH,titratable acidity,water-holding capacity,and color difference)and textural characteristics.And its influence on the internal structure of yogurt was explored by measuring the potential,particle size,hydrophobicity,microstructure,and protein secondary structure.The results showed that with the increasing of SPI substitution(0%to 50%),the sensory quality of the yogurt was improved,and the structural properties was enhanced.The titratable acidity of the yogurt decreased by 17.66°T(P<0.05),and the water holding capacity increased to 59.17%(P<0.05).The textural properties were all enhanced(P<0.05),and the particle size and zeta potential increased significantly(P<0.05).In terms of physical structure,as the substitution amount of SPI increased,the soy protein and casein in the yogurt cross-linked with each other to form curd with dense network,which was better than conventional yogurt curd at 30%substitution of SPI,and closer to tofu curd when adding 50%substitution of SPI.In terms of chemical structure,theβ-fold content tended to decrease with increase of SPI substitution,while the relativeα-helix,β-turn and random curl increased in varying degrees.The addition of SPI significantly enhanced the physicochemical properties and curd structure of the yogurt,and 30%was the optimal substitution amount of SPI.