Screening Of Cheese Starter And Study On Processing Technology Of Cheese

In this research lactic acid bacterial that suited for the starter of cheese-making was isolated and screened from the characteristic diary products produced by the minority of xinjiang province. The character of the starter and the rennet used in the experiment, the processing technology of the cheese and the physicochemical characteristics and microorganism changes during the ripening process of cheese was studied. The project included several parts such as:1. 44 stains lactic acid bacterial were isolated from 15 samples of dairy and dairy products, which produced by the Kazakstan herdsman living in the nanshan pasture area which lies to the south of the shihezi city of xinjiang province. And among them 25 were bacilli and 19 are cocci. According to their characteristics of morphology, physiology and biochemistry they were ascribed to 4 genuses of Lactobacillus, Lactococcus, Enterococcus and Leuconostococcus. In bacilli, 7 strains were Lactobacillus casei, 7 strains were Lactobacillus plantarum, 3 strains were Lactobacillus helveticus, 1 strain was Lactobacillus curvatus, 5 strains were Lactobacillus coryniformis subsp and so forth. In cocci, 6 strains were L.lactis subsp. Lactis, 4 strains were L.lactis subsp and so on..2.The ability of fermenting milk to produce acid, viscosity, diacetyl and proteolysis was tested by experiments. L.lactis subsp was screened from 7 stains lactic acid bacterial which contain Lactobacillus plantarum, Lactobacillus coryniformis subsp,Lactobacillus casei, Lactobacillus helveticus, Lactobacillus coryniformis subsp, L.lactis subsp. Lactis and L.lactis subsp, and confirmed the suitable starter for cheese making. Further investigation on the property of the starter showed that the starter had maximum cell number and acid-producing ability when cultured at 32℃.3. The activity of rennet was 55556U/mL at the temperature of 35℃. The influence of temperature, pH value and the addition amount of CaCl₂ on the activity of rennet was studied. The optimum gel formation condition of milk was that pH value was between 5.6～6.0, the temperature is at 38～42℃and the addition amount of CaCl₂ was 10g/100L.4. In order to improve the texture and flavor of cheese,experiment was conducted to determine the optimal technology. The optimal technological parameters were that the addition amount of rennet were 3g/100Kg,at absence of CaCl₂,the concentration of NaCl are 20% and ripening at the temperature of 7℃. And the addition amount of rennet and the ripening temperature had more important influence on the character of cheese.5. Through studying the value changes of physico-chemical characteristics and microorganism under optimal technological conditions during cheese ripening, experiment results showed that pH 4.6-SN of cheese increased gradually at first and subsequently slowly raised, while 12%TCA-SN of cheese increased continually. The hardness gradually decreased but had no significance. The total acid increased quickly at first, afterward it increased slowly and at last kept stable. The value of pH decreased in the first week, but from the second week, it increased gradually to the top at the fifth week, lately it slowly reduced and kept invariable. The number of lactic acid bacteria gradually reduced at first and kept stable in the main subsequently. From these changes, we could see the optimum ripening time of cheese was about 6 weeks.