Evaluation Of Different Processing And Modification Methods And Physicochemical Properties Of Natural Milk Fat

As an important component of milk,milk fat is the main source of energy and flavor in dairy products.However,the domestic research on milk fat started late,and the existing milk fat products are relatively simple,which couldn’t meet the needs of industrial food processing and seriously restrict the development of milk fat industry.Therefore,in this study,the milk fat was separated to a certain extent by modification methods such as dry fractionation,short-path molecular distillation and enzymatic hydrolysis,and the changes of physical and chemical properties of milk fat component s after different modification methods were analyzed,in order to develop milk fat products for different needs and provide theoretical guidance.The specific results of the experiment are as follows:Firstly,the milk fat was modified by dry fractionation,and the physicochemical properties of each fraction and the application properties of the fractionated high melting point fraction were studied.The results showed that with the decrease of the fractionation temperature,the melting point of each fraction decreased,the content of long-chain saturated fatty acid decreased,and the content of short and mediumchain saturated fatty acid and unsaturated fatty acid increased,and the corresponding triacylglycerol content containing saturated fatty acid also decreased.The crystal structure of milk fat was determined by X-ray diffraction(XRD),the results showed that the high melting point fraction was a mixed crystal form dominated by β’ crystal form at room temperature,while the low melting point fraction did not crystallize.Homogenous polycrystalline phenomenon of milk fat was studied by differential scanning calorimeter(DSC).It is found that the crystallization and melting temperatures of the high melting point fractions are relatively higher and the latent heat of phase transition is larger,while the low melting point fractions is lower and the latent heat of phase transition is smaller.All of those results indicated that the higher of the saturation degree of milk fat,the higher of the melting point and the crystal stability,the greater of the relative hardness and the enthalpy required for the crystallization and melting process,which is suitable for the preparation of products with higher melting point requirements.Therefore,the highmelting point fraction 30 S was made into high-melting-point butter flakes,then observed its apparent properties,and researched the application characteristic when applied in croissants and butterflies which required high-temperature baking.Compared with the commercial products with high melting point,the crispness,acceptability and application were better.Secondly,the short-path molecular distillation technique was used to separate the milk fat,and the relationship between each distillation and the distillation substrate and temperature were analyzed.In terms of chemical composition,distillation does not change the composition of fatty acids and triacylglycerols,but separates milk fat to a certain extent in terms of molecular weight.As for physical composition,the crystallization melting of milk fat is related to the change of triacylglycerols.With the increase of distillation temperature,the melting peak shifts from the low temperature region to the high temperature region.XRD showed that the crystallization mainly occurs in the retentate,but the light phase fraction crystallization hardly occurred,because the large molecular weight substance mainly aggregated in the retentate,which was consistent with the results for triacylglycerols.Therefore,in practical applications,the yield of distillation and their processing properties can be comprehensively considered in order to find a distillation temperature suitable for actual needs.Besides,The content of OPO(18:1/16:0/18:1)and OPL(18:1/16:0/18:2)of triacylglycerols in the retentate increased significantly after short-path molecular distillation,which is very important for infants and young children.The result has important guiding significance for the research and development of infant milk powde.Finally,using milk fat to prepare natural milk flavor essence has been a research hotspot.The milk flavor essence prepared by enzymatic hydrolysis of milk fat by lipase has a rich and natural aroma,apply to food as food additive can solve the problem of food processing with low fat content but sufficient frankincense flavor.In this study,using the enzyme modification technology to enzymatically hydrolyze milk fat,three kinds of lipases include NUO Palatase 20000L,lipase AY and lipase MER were selected to simultaneously hydrolyze 99.9%fat content of anhydrous milk fat and 83%fat content of butter.After enzymatic hydrolysis,the free fatty acids of the two substrates changed significantly,the contents of the four main short-chain free fatty acids include butyric acid,caproic acid,caprylic acid and capric acid,which provide flavor substances,were significantly increased.In anhydrous milk fat,the enzymatic hydrolysis ability of lipase MER and lipase AY were stronger than that of NUO Palatase 20000L.Among butter,the enzymatic hydrolysis ability of lipase MER is the strongest,and the overall enzymatic hydrolysis effect of anhydrous milk fat is better than that of butter.The flavor of anhydrous butter was analyzed by electronic nose,and it was found that the flavor of different enzymes at different times were different except for the similar enzymatic hydrolysis effects of the three enzymes at 10 h.This study can provide more theoretical basis for the enzymatic hydrolysis of milk fat to enhance flavor.