Studies On The Critic Procedures Of Quarg Cheese Processing

Quarg cheese is one of the most important fresh cheeses, which is originated in Germany. As a wholesome low calorie food, it has a relatively strong market potential in our country.This dissertation intensively studied the critical parameters which are of great importance to Quarg cheese, include the species and ratio of starter cultures, the amount of coagulant, the parameters of sterilization, cut pH and centrifugation to investigate their effects on Quarg cheese. The results are as follow: the addition of small amount of Streptococcus thermophilus to the starter culture of Quarg cheese can remarkably improve the corrected yield as well as reduce the wheying-off during the storage of Quarg cheese., when the ratios of Lactococcus lactis subsp. Lactis to Streptococcus thermophilus are 1 : 0, 125 : 1, 25 : 1,5: 1,1 : 1, the ratio of 25 : 1 is the best one for Quarg cheese. The addition of small amount of rennet can remarkably improve the corrected yield, the recovery rate of protein and solids, and not affecting the proteolysis during the storage of Quarg cheese, the appropriate amount of rennet is 40RU/100L milk. The heat treatment of raw milk can remarkably improve the corrected yield of Quarg cheese, and of the three kinds of heat treatment (63 ℃, 30min, 85 ℃, 20min, 95 ℃, 5min), the best one is 95 ℃, 5min. The cutting pH can remarkably affect the corrected yield and sensory property of Quarg cheese, in the range of 4.7-4.5, the higher the cutting pH, the cheese becomes more granular and the yield becomes lower, when the cutting pH is 4.5, the cheese becomes over acid, the cutting pH of 4.5-4.6 is preferred. The centrifugation can also affect the Quarg cheese remarkably, and when the centrifuge force is 300g, time is 20 min, the chemical composition of the product is accordant with the typical Quarg cheese.An experiment was designed to optimize the key parameters of Quarg cheese. The results indicated that for the sensory property of Quarg cheese, the sequence of the parameters is : cutting pH>heating time > rennet amount> heating temperature(the parameters are sequenced by their effect intensity), and the best combination is 4.60, 5min, 30RU/100L milk, 55 ℃ for the aforesaid parameters. For the corrected yield, the sequence of the parameter is rennet amount>heating temperature>cutting pH> heating time, and the best combination is 50RU/100L, 55 ℃, 4.50,5min. For the WSN content, the sequence of the parameters are rennet amount>heating time>heating temperature>cutting pH, and the best combination is 30RU/100L milk, 55℃,10min. Combined the three index, the optimized parameters are 30-40RU/100L milk for the rennet amount, 4.55-4.60 for the cutting pH, 60℃,10min for the heat treatment of the curd.