Research On Yak's Milk Soft Cheese Technology And Flavor Compounds In Ripening Process

Soft cheese was made from Yak`s milk in Gannan pasturing area, and its processing technics were optimized. Analysis the physicochemical determinations and volatile flavor compounds change regular pattern with different ripening temperature and time. The main results include following aspects:1. Optimize the process technical of Yak's milk soft cheese, finally confirm the best technics parameter: added rennet at 100.9 U/mL, starter at 0.03 g/L, clabber temperature at 34℃, pH at 5.8 and CaCl2 concentration at 0.02 g/100mL.2. Measured the moisture, ash, fat, protein (pH4.6-WSN,12% TCA-WSN), FAA of cheese samples with different ripening temperature (5,10,15℃) and time (0～90d), etc. The results indicated that the higher ripening temperature, the sharply decrease moisture content of samples. With three different ripening temperature, the tendency was similar about ash which showed an upward trend after the first reduction. The fat content tendency was also decreased with the extension of ripening time. The pH4.6-WSN, 12% TCA-WSN, FAA were rapided increase during ripening time. Combined with sensory evaluation of Yak`s milk soft cheese obtaining the best maturity time was 3 months, in 10℃storage conditions, a good mature cheese sensory characteristics and moderate hardness.3. The flavor compounds in Yak`s milk soft cheese were extracted by simultaneous distillation-extraction (SDE) equipment. Screening the extraction time were optimized experimental conditions, results showed that the distillation time was 5h would be more appropriate. The 63, 56 and 41 flavor compounds in which were identified by gas chromatography-mass spectrometry (GC-MS) analysis on the conditions of 5,10 and 15℃storage. Besides, the relative content of each compounds was determined by area normalizing method.4. The soft cheese on the conditions of 5,10 and 15℃storage, the flavor compounds were extracted by solid phase microextraction (SPME) in which 32, 46 and 33 compounds and identified by gas chromatography-mass spectrometry (GC-MS) analysis. Besides, the relative content of each compounds was determined by area normalizing method. Screening the extraction fibres and temperature of solid phase microextraction were optimized experimental conditions, the results showed that the flavor compounds were good extracted by 75μm CAR/PDMS and temperature 50℃.5. The main volatile compounds in Yak's milk soft cheese were acids, alcohols and ketones, secondly volatile compounds were esters and aldehydes. The content of caproic acid, octanoic acid, decanoi cacid, 2-heptanone, 2-undecanone, 2-tridecanone and 2-pentadecanone in the cheese samples is relatively higher which constituted the main flavor compounds of Yak`s milk soft cheese.