Studies On The Stability Of Fermented Milk Beverage By The Addition Of Whey Protein Concentrate

Whey protein concentrate was widely used in fermented milk beverage (FMB), but the effects on the stability of the products were rarely reported. In this paper, the effects of WPC types, adding methods and usage of WPC, acidification and heat treatment on the particle size, the change rates of particle sizes,ξ-potential, free sulfydeyl, surface hydrophobicity index, protein particle state and rheological properties were studied. The results may provide a theoretical basis for the industrial production of FMB.Four types of WPC34, WPC70, WPC72and WPC80were chosen as the object of this study to examine the effects of different types of WPC on the stability of FMB. The results showed that:among the four types of WPC chosen in the test, WPC72made the best stability of the products; The influence of the amount of WPC used on the stability of FMB was related to the type of WPC, the product had the best stability when WPC72provide protein content was0.3%. It was beneficial to the stability of the product when WPC added to the FMB before fermentation.For the samples which WPC was added before fermentation, protein network structure had formed in the process of yoghourt making and subsequent acidification would not make large effects on the stability of FMB. In the process of acidification, particles size and free sulfydeyl only slightly changed,ξ-potential reduced gradually, surface hydrophobicity increased and the distribution of protein particles became more uniform. The main effects of heat treatment on the stability of FMB system showed in the aspects of particle size, free sulfydeyl content and surface hydrophobicity etc but ξ-potential didn’t change greatly. When the heat treatment condition was95℃5min, particle size and free sulfydeyl content got its minimum value, surface hydrophobicity index got the maximum value and protein particles had the best dispersibility.For the samples which WPC was added after fermentation, acidification and heat treatment had a great influence on the stability of FMB system. Particle size and free sulfydeyl content decreased at first and then increased during acidification. When the pH value was about3.9, particle size and free sulfydeyl content reached the minimum. The value of ξ-potential was reduced continuously and hydrophobic gradually increased during acidification but when pH was about3.9hydrophobic wasn’t increased substantially any more with the acidification. At the same time CLSM photos also showed protein aggregation state appeared first dispersion state with the decrease of pH, when pH was about3.9sample had the minimum particle size and the best dispersion. The effects of heat treatment on the stability of FMB were similar to the samples which WPC was added in the form of fermented and the difference was the degree of the influence. Each index fluctuate greatly for the samples which WPC was added in the form of unfermented and that indicated free whey protein structure was instable when heating.FMB system was typical pseudo plastic fluid. The acidification process, the increasing use of WPC and heat treatment temperature would lead to K decrease and liquidity of the system was enhanced. The value of n decreased with WPC usage increases and system had clearer pseudo plasticity. On the contrary, the value of n decreased with the heat treatment temperature increases, and the pseudo plasticity of the system weakened. At low shear rate the amount of WPC addition had no effect on the system energy storage modulus G’ but it increased with the increasing of WPC amount at high shear rate, which means system elasticity increased gradually. Besides, G" increased with the increasing of shear rate. When the amount of protein provided by WPC was0.3%, G" got the minimum value and the system became the most easily flow.