| Milk-clotting Enzyme is a key enzyme in cheese processing,among which calf rennet is a common commercial chymosin,but there are problems such as insufficient supply and high cost,so it is necessary to further develop new resources chymosin.In the early stage,the research team obtained chymosin from Moringa oleifera seeds.The main functional component was identified as aspartic endopeptidase,and its molecular characteristics and chymosin characteristics were revealed,which could be used in cheese processing.In this thesis,Moringa oleifera seed chymosin was applied to the processing of buffalo milk cheese,and the optimum parameters were determined through the optimization of processing technology,so as to further evaluate the influence of Moringa oleifera seed chymosin on cheese quality characteristics,provide reference for the development of new chymosin resources,and further improve the comprehensive utilization rate of Moringa oleifera protein resources.The specific research results are as follows:follows.1.Optimization of processing technology of buffalo cheese.The regression equation model of curd p H,chymosin addition and curd time on sensory score and degree of hydrolysis was established by single factor test combined with response surface analysis.The optimum technological parameters of Moringa oleifera seed rennet cheese were as follows: p H value of rennet was 5.56,rennet dosage was 0.14%,and rennet time was 32 min.Under these conditions,the theoretical sensory score of buffalo milk cheese was 75.5 points,and the degree of hydrolysis was 12.56.Further,1600 peptides with molecular weight less than 3 k Da were identified from the water-soluble peptides of cheese by LC-MS/MS,and the activity prediction showed that 613 peptides had good biological activity,of which 43 peptides were reported functional peptides.2.Optimization of buffalo cheese processing technology.(1)Physico-chemical composition and functional characteristics: The content of ash,fat and protein in the cheese processed by Moringa oleifera seed chymosin was similar to that of calf chymosin,but the moisture content was significantly higher than that of calf chymosin(P <0.05);There was no significant difference between the two kinds of cheeses in oil precipitation,meltability and drawability(P >0.05).(2)Texture and structural characteristics: The analysis of sensory texture parameters of cheese by texture analyzer shows that there is no significant difference in elasticity,cohesiveness and resilience between the two kinds of cheese,while the hardness,adhesiveness and chewiness of cheese processed by calf chymosin are significantly higher than those processed by Moringa oleifera seed chymosin,indicating that the cheese processed by Moringa oleifera seed chymosin is softer and easier to chew;Scanning electron microscope(SEM)showed that the cross-section of cheese processed by Moringa oleifera seed chymosin was small and evenly distributed,and the network structure was compact,forming a smooth and delicate texture.Rheological analysis shows that the G’>G’’of cheese samples processed by Moringa oleifera seed chymosin has more elastic components than viscous components,forming an elastic gel with better stability.(3)Flavor and quality characteristics: 25 kinds of free amino acids were detected in the cheese processed by Moringa oleifera seed chymosin,among which the contents of phosphoserine and glutamic acid were significantly higher than those of calf chymosin(P<0.05),and 8 kinds of characteristic free amino acids were screened out from the 25 kinds of free amino acids.At the same time,17 kinds of free fatty acids were detected,among which the contents of medium-chain fatty acids,long-chain fatty acids,total free fatty acids,saturated fatty acids and monounsaturated fatty acids were high(P <0.05),and 4kinds of characteristic free fatty acids were screened out from the 17 kinds of free fatty acids.A total of 45 volatile flavor compounds were detected by GC-MS,including 9hydrocarbons,6 alcohols,8 acids,6 aldehydes,6 ketones,8 esters and 2 lactones,and 17 characteristic volatile flavor compounds were screened out.The analysis of characteristic flavor substances shows that there is a certain correlation among free amino acids,free fatty acids and volatile flavor substances.3.Storage and analysis of buffalo cheese.During the 21 day storage period,the sensory scores of both types of cheese continued to decrease during the storage period;The p H values of the two types of cheese first increased and then decreased,reaching their maximum value on the 15 th day;The color change of the two kinds of cheese during storage showed a trend of first rising and then declining.Calf Chymosin cheese had a large color difference between 6-15 days,and horsewood seed Chymosin cheese had a large color difference between 9-18 days;The colony number of the two kinds of cheese continued to increase,and the growth rate was fast in the middle storage period.The total colony number of cheese processed by horseradish seed Chymosin was greater than that of calf Chymosin. |
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