Manufacture Procedures Of Quark Cheese By Ultrafiltration

The Quark cheese with the mildly acidic flavour is one kind of low fat, high calcium and protein dairy product, which is easily digested and popular with people. The high quality Quark should be smooth and easy to be spreaded. It is usually mixed with cream and consumed in various family dishes. The traditional Quark cheese is cultured with Streptococcus lactis and Streptococcus cremoris, combined with Streptococcus diacetilactis and Leuconostoc citrovorum or not, to produce lactic acid and form coagulation. The incubation time of traditional method is long, the starter culture is easily contaminated and the culture preserved condition is strict, which has increased the production cost, moreover the yield is low. Gluconic acid lactone with membranetechnology was used in this experiment to simulate traditional starter culture for producing acid, to avoid many disadvantages of traditional method, to reduc the cost, to enhance the yield and to favor the continuous industrial production.The milk was concentrated by ultrafiltration. Gluconic acid lactone was used to substitute the traditional starter culture to produce lactic acid. The critical technology parameters were optimumed that influence the Quark cheese chemical compontent, the incubation time, the yield and the sensory quality, including ultrafiltration factor, the temperature of sterilization and the dosages of gluconic acid lactone and rennet.The acid-produced speed of retentate gradually reduced with ultrafiltration fold increasing. The milk pH was very difficult to reach 4.6 when concentration fold reached 3 times and above; the adjustment yield enhanced 2.86% compared with the traditional method when concentration factor was 3, but sensory quality was relative bad.The adjustment yield obviously enhanced 2.17% when the gluconic acid lactone substituted traditional starter culture. The product with best sensory quality could be obtained from the milk pH5.6 and 0.3% of gluconic acid lactone.The rennet could enhance Quark cheese yield, reaching highest yield when rennet level was 200μl/100g. The product hardness increased with the increasing rennet level. The bitterness became more obvious with the storage time extension.Different sterilization processing raw milk indicated the high temperature could obviously enhance the yield, the total solid returns-ratio and the protein returns-ratio. The microstructure of product was more exquisite, but the sensory quality was still inferior to the pasteurization product.Through the orthogonal experiment of critical technology parameters, the influence extent on the sensory quality was in the decenting order of curd temperature, whey separation condition, the posterior heat treatment time and the posterior the heat treatment temperature, the optimal combination was: 45℃of curd temperature, 50℃of posterior heat treatment temperature, 5min of posterior heat treatment time, 3600g/20min of whey separation condition; the influence extent on the product adjustment yield was in the decenting order of curd temperature, posterior heat treatment temperature, whey separation condition, and posterior heat treatment time. The optimal combination is: 35℃of curd temperature, 50℃of posterior heat treatment temperature, 5min of posterior heat treatment time, 3000g/20min of whey separation condition. Based on the sensory quality and the adjustment yield, the best procedure combination was: 35~45℃of curd temperature, 50℃of posterior heat treatment temperature, 5min of posterior heat treatment time, 3000～3600g/20min of whey separation condition.