| The fresh cheese is consumed without storage or aging. It is manufactured by fermentation of lactic acid bacteria and addition of a small amount of rennet. Fresh cheese is packed after whey separation from the curd.Fresh cheese is tasted with sour feeling and daintily and preferred by many customers. However, it has bad propertise with whey-off during shelf life because of high water content. it has high water content but low water holding capacity(WHC), resulting in bad texure Although the influences of external factors as incubation temperature,homogenization pressure,strains,stabilizers on the formation of fresh cheese have been studied, the internal factors including milk protein, milk fat and ratio of casein and whey protein were seldom investigated. Especially the milk protein is the primary substance for forming cheese gels, and has the most direct impact on the physical chemistry properties and microstructure of cheese gels.Several factors were examined in this experiments, including ultrafiltration of raw milk, addition of skim milk powder (SMP), addition whey protein concentrate powder(WPC80) and addition of a food thickener to improve water holding capacity of fresh cheese(WHC), microstructure and sensory.1.Ultrafiltration of raw milk: the water holding capacity of fresh cheese (WHC) was increased and reduced later with the increase of CF. The Maximum of WHC was 92.37% when CF was 3. Hardness, viscosity and colloid texture of fresh Cheese were also optimal. Taste and smell of fresh cheese ultrafiltrated were inferior to control group. When CF was 3 the yield reached the maximum 24.71%. The microstructure was more regular and denser with the increase of CF, but destroyed when CF was 4. So the optimal CF is 3.2. Skim milk powder (SMP) strengthening milk protein with the increase of addition level of SMP, the water holding capacity of fresh cheese significantly increased; and the maximum value was 91.85% when the addition level of SMP was 4%. The hardness, viscosity, and gel-property of fresh cheese were proportional to the addition level of SMP, and the maximum value appeared when the addition level of SMP was 5.5%. The result of sensory evaluation is optimal when the addition level of SMP was 4%. The yield of fresh Cheese was proportional to the addition level of SMP, the value achieved 22.90% when the addition level of SMP was 5.5%. With the increase of addition level of SMP, the microstructure of the gels was denser and more ordered. Finally the optimal addition level of SMP was determined as 4%.3. Whey protein concentration powder (WPC80) strengthening milk protein: With the increase of addition level of WPC80, the water holding capacity of fresh cheese significantly increased; and the maximum value was 91.02% when the addition level of WPC80 was 3%. The hardness of fresh cheese was proportional to the addition level of WPC80, and the maximum value appeared when the addition level of WPC80 was 4%; and the viscosity and gel-property of fresh cheese were optimal when the addition level of WPC80 was 3%. In addition, the 3% addition level could optimize the flavor of fresh cheese and increase the yield of fresh cheese to 24.93%. What's more, the microstructure of the gels was dense and had lots of branches when the addition level of WPC80 was 3%. At last he optimal addition level of WPC80 was determined as 3%.4. Determine the optimum proportion of casein and whey protein: when casein: whey protein was 1︰1, the water holding capacity of fresh cheese significantly increased to the maximum 92.54%. When casein︰ whey protein was between 1︰1 and 2︰1, texture parameters were optimal. In addition, when casein︰ whey protein was 2︰1, sensory quality of fresh cheese was significantly increased and the microstructure of the gels was dense and ordered. Then casein︰ whey protein was 3︰1, the maximal yield of fresh Cheese was 24.03%. At last optimum proportion of casein and whey protein was determined as 2︰1.5. Addition of food thickening agents: adding 0.2% food thickening agents (carrageenan︰ sophora bean gum=1︰1) could improve the water holding capacity of Fresh Cheese and increase the yield of fresh cheese. However the effect of ameliorating the sensory quality was unremarkable.It was concluded thatprotein content in cheese milk have a significant effect on the water holding capacity and rheological texture, particarly by enhancing whey protein content with suitable ratio of caisein to whey. Food thickeners play a slight role in improving the water holding capacity and eating quality, but inferior to whey.
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