Optimization of the Fermentation Process of Industrialized Independent Fermentation Coagulated Fermented Milk by Response Surface Methodology

Industrialized independent fermentation coagulated fermented milk is prone to the phenomenon of excessive whey precipitation and poor coagulation state of the finished product affected by factors such as fermentation temperature fluctuation, fermentation time and shear damage after fermentation. The effects of fermentation temperature fluctuation, fermentation temperature, fermentation time, fermentation strain ratio, and simulated industrial filling damage on product texture and flavor were studied. On the basis of single-factor experiments, a response surface methodology Box-Behnken combination experiment was designed. The process parameters of fermentation temperature, fermentation time and fermentation strain ratio were optimized. The single-factor experiment results showed that the shear damage had little effect within 2 hours of fermentation after filling, but it could seriously affect the product texture and acidification speed when the time exceeded, suggesting that in the industrial fermentation process, the temporary storage time of the liquid milk in the room temperature environment should be shortened as much as possible, and the liquid milk waiting for filling delayed over 2 hours due to machine failure should be directly fermented into finished products for secondary use. It wasn’t suitable for filling after cutting through the pipeline. The results of the optimal solution of the response surface model showed that the texture integrity rate of the industrialized independent fermented coagulated fermented milk prepared under the optimal technological conditions of the actual fermentation temperature of 42 ℃, the fermentation time of 5.6 h, and the bacterial species ratio of 1:1 was 100%, the acidity of terminating fermentation was 68.56°T, and the acidity of 12 h after cold storage was 70.2°T. The comprehensive sensory score of fermented milk was 8.24, which was close to the predicted value, proving the validity of the model. The results of the rheological characteristic curve showed that the fermented milk had weak shear resistance, and the yogurt viscosity recovery rate after 200 s⁻¹ high shear was only 25.55%, which was in line with the sensory characteristics of the coagulated fermented milk in the form of crisp, soft and smooth. The response surface methodology can effectively fit the relationship among the fermentation temperature, fermentation time and fermentation strain ratio of the coagulated fermented milk. It provides certain theoretical guidance for the unavoidable error of strain proportioning and weighing, the fluctuation of fermentation temperature and heat transfer, and the error of fermentation time caused by artificial sampling opportunity in industrial production, which is convenient for putting forward corresponding countermeasures quickly in practical operation.