Stabilizing Mechanism Of Set Yoghurt Induced By γ-Polyglutamic Acid

y-Polyglutamic acid is a new stabilizer, it can improve the two main problems cxsit in set yoghurt including acidic denaturation of lactoprotein and whey separation, meanwhile it also can provide certain theoretical basis and guidance for the production and process optimization of high quality fermented dairy production. In this research, different concentrations of γ- polyglutamic acid (0%～0.08%, a gradient for 0.02%, w/w) were added to the set yoghurts which were investigated from texture, thermodynamics, reology and micro perspective, aiming’to study the stabilizing mechanism of set yoghurt induced by γ-polyglutamic acid. Firstly, the texture properties of set yoghurts with different concentrations ofy-polyglutamic acid were determined, and results indicated that proper concentrations of γ-polyglutamic acid could strengthen the hardness, adhesiveness, gumminess and chewiness of set yoghurts. Then the thermodynamics results pointed out that the addition of γ-polyglutamic acid would make phase transition of the yoghurt systems occurred more easily before fermentation and lead to longer phase transition after fermentation. Then the flow, thixotropy, and viscoelasticity properties of all set yoghurts were studied using rheo meter, and the results demonstrated that the addition of γ-polyglutamic acid had a positive effect on the anti-shear ability of set yoghurt systems, but it could weaken the viscoelasticity properties of them which meant that γ- polyglutamic acid had an interference effect on the formation of network structure. In this research, Zeta potential and particle-size measurement were applied to discuss the interaction between γ-polyglutamic acid and casein, then the scanning electron microscope (SEM) was adopted to observe the network structure. Those results confirmed that suitable concentrations of γ- polyglutamic acid could improve the stability of set yoghurt systems. Later, the results obtained by measuring the change of pH value, acidity, viscosity, water hold capacity and sensory evaluation of all samples during storage revealed that y-polyglutamic acid could significanmy improve the refrigerated stability of yoghurts. Finally, headspace solid phase micro-extraction combined with gas chromatography-mass spectrometry was used to analyze the volatile compounds of set yoghurts, and the final results showed that the addition of γ- polyglutamic acid could significantly increase the varieties of volatile compounds in set yoghurts within certain limits. Furthermore, compared to the controlled sample, the content of all the volatile compounds in set yoghurts added with γ-polyglutamic acid were lower.