Study On Processing And Quality Control Technology Of Long-shelf High-protein Yoghurt

Long shelf life yoghurt is a kind of high-selling product on the market.It has developed rapidly in recent years.The difference between long shelf life yoghurt and traditional chilled yoghurt is that the long shelf life yoghurt under secondary sterilization stored at room temperature has the high content of modified starch.The taste is poor,which reduces the consumer's preference.In order to develop a long shelf life yoghurt with high quality and good taste,this topic adds protein to the raw milk by adding MPC.Since MPC has good gel and emulsification compared with other substances that can improve protein,it can improve the texture,viscosity,stability and taste of yoghurt protein at the same time.It can also improve the problem of poor taste caused by excessive content of modified starch.In addition,the subject concentrates the raw milk by membrane technology,improves the protein content of the milk product without adding a stabilizer,and simultaneously sterilizes the milk product,thereby effectively increasing the protein and taste of the yogurt and prolonging its Shelf life.Based on the above reasons,this study studied the processing technology and quality control technology of long shelf life high protein yogurt,hoping to provide guidance for the production of long shelf life yogurt.The main research and results of this topic are as follows:(1)Through the response surface optimization experiment to optimize the preparation process of long shelf life high protein yogurt,it is found that the influence degree of each factor on the sensory score of long shelf life yogurt is: total protein addition amount > the amount of modified starch > the amount of agar added,according to the senses The optimal process values obtained from the evaluation results were: the addition amount of protein was 5.64%,the addition amount of modified starch was zero,and the addition amount of agar was 0.6%.It was found by verification experiments that the sensory evaluation result obtained under this condition was 89.4.There is no significant difference from the theoretical prediction value of 90.1.(2)From the sensory evaluation,acidity,p H value,viscosity,water holding capacity and microbial indicators,the long shelf life high protein yogurt prepared by the above process conditions and the commercial long shelf life yogurt were compared during the 75 d storage period.The results showed that,similar to the commercially available yoghurt,the MPC protein-fortified yoghurt had sensory indexes that were more acceptable to consumers,and the sensory score was higher;and the stability was better than the commercially available long-life yoghurt,during the 75-day storage period.(3)The use of microfiltration technology to concentrate the raw milk to increase the protein content of the milk,and then use the micro-filtered milk to produce yogurt.The milk microfiltration of the milk is 0.2 ?m ceramic membrane,the temperature of the liquid is kept at 50? by heat exchange,and the pressure difference between inlet pressure and outlet pressure is 0.1 MPa.The concentration times of 2× and 3× are 60 min and 116 min,respectively.The flux of 2× concentrated membrane is basically maintained at 77 L/(m2·h),and the flux of 3× concentrated membrane is basically maintained at 61.5 L/(m2·h).The content of solids,protein and fat in each concentration multiple retention liquid increased significantly with the microfiltration,but there was no significant difference in the lactose content between the raw milk and each concentrated retentate;as the concentration multiple increased,the rates of lactose,ash and minerals have increased to varying degrees,but not completely.The long shelf life high protein yogurt produced by different concentrations of milk after microfiltration was compared in acidity,p H value,viscosity,water holding capacity,sensory evaluation and microbial index in 75 days at 4? and 25? storage temperature.The results showed that the higher the concentration of the cow's milk,the more stable the yogurt,but because the protein content of the 3× concentrated milk was too high,it was 9.02%,which led to a decrease in the hard taste score of the product.Therefore,the 2× concentrated milk,the protein content was 6.32%,this product is manufactured to ensure stability during storage,as well as good taste and sensory score.It is also found that yogurt stored at 4? has a more acceptable sensory evaluation index and stability than yogurt stored at 25?.(4)By measuring the rheological parameters of high-protein yogurt during fermentation,it was found that protein-fortified yogurt has greater storage modulus and loss tangent than non-protein-fortified yogurt,and higher shear stress values.Long shelf life high protein yogurt produced by the membrane concentration process,with the increase of the raw milk concentration multiple,the yogurt has greater storage modulus and loss tangent,and higher shear stress values.And storage modulus,loss tangent and shear stress values increase with increasing protein content,and both methods of strengthening the protein improve the hardness and taste of the product.