Effect Of Fermentation Amount And Maturity Time On Fat Degradation Of Yak Milk Hard Cheese

In this experiment,fresh yak milk from Zhuaxixiulong Township of Gansu Tianzhu was used as raw material,and 1.0%,2.0%,and 3.0% fermentation doses were added to make three kinds of yak milk hard cheese.The microstructure of yak milk hard cheese was determined by laser confocal scanning microscopy during the ripening of yak milk hard cheese for 0?90days.The change of fatty acid in cheese was determined by gas chromatography-mass spectrometry.And the effect of maturity time on the physical and chemical properties,texture,microstructure,color and fat degradation degree of yak milk hard cheese.The main research results are as follows:(1)When the fermentation dose of 2.0% is added,the yield of yak milk hard cheese is the highest;when the amount is 3.0%,the yield is the lowest.The 1.0% starter added amount of cheese has the lowest moisture content but its p H,Na Cl content and fat content are higher than the other two cheeses.With the prolongation of maturity,the p H value of cheese first decreased and then increased,water and fat content decreased,but Na Cl content increased.(2)The chromaticity in the 3.0% starter added amount of cheese was less than 1.0% and2.0% of the added color in the cheese throughout the ripening process.3.0% starter added amount of cheese hardness,elasticity,cohesiveness and chewiness were less than 1.0% and2.0% added cheese in mature 0?90 d.With the increase of maturity time and the increase of fermentation dose,the microstructure of cheese is affected and the particle size of fat globule is increased,which makes the cavity larger and the structure loose.The total number of colonies decreased with the prolongation of maturity.The total number of colonies in 3.0%cheese and the total number of lactic acid bacteria colonies were higher than 1.0% and 2.0%in the whole ripening process,indicating that the high amount of starter added can accelerate the oxidation of fat in cheese.(3)The 3.0% oxidizer addition amount of the lipoxygenase activity in the cheese was significantly higher than the esterase activity in the 1.0% and 2.0% cheese at 90 days of ripening(p < 0.05).As the maturity time increases,the ADV,CV,and TBA values in the cheeses of the three starter additions also increase.The 3.0% increase was significantly higher than 1.0% and 2.0%(p < 0.05).Cheese POV increased first and then decreased with the prolongation of maturity time,and the value was the highest at 60 d.(4)The contents of TFA,SCFA,MCFA,LCFA,SFA,MUFA and PUFA in the 3.0%added cheese were significantly higher than those in the 1% and 2% starter cheese(p < 0.05).The amount of starter added can promote the degree of fat degradation in cheese,and with the increase of maturity time,the contents of TFA,SCFA,MCFA,LCFA,SFA,MUFA and PUFA in the three cheeses also showed an increasing trend,indicating the maturity time and The amount of starter added has a synergistic effect with the oxidative degradation of yak milk hard cheese fat.