The Research Of Liquefaction Of Lard And Its Rheological Properties

Melting point is determined by the fatty acid composition saturation and carbon chain length of the fat, to reduce the melting point, the key is to remove long-chain saturated fatty acid. It is of great significance in terms of improving its edible, developing of high value-added products when used in food industry. Based on this, commercial refined lard was used as the research object, we used the methods of acidolysis reaction,chemical interesterification by different catalysts and means of rheology, thermodynamics to research the methods of reducing the melting point of lard. The mainly content of this study as following:aspects carried out:Sodium methylate catalyzed chemical interesterification of lard and soybean oil; Sodium methylate catalyzed chemical interesterification of solid fat (which got from dry fractionation) and methyl caprylate; Immobilized lipase Lipozyme TL IM catalyzed acidolysis reaction (which got from dry fractionation) and caprylic acid;the study of rheological properties of modified oil;the evaluation of physicochemical and thermodynamic properties of modified oil.The contents and results are as follows:With sodium methoxide as catalyst, using technology of chemical interesterification to study the effect of temperature, the interesterification time, catalyst amount on melting point, acid value Etc of the product that got from the chemical interesterification of lard and soybean oil, and determine the factors and levels according to single factor orthogonal experiment, get the best process conditions for:interesterification temperature 70 ℃, interesterification time 2 h, the amount of catalyst is 0.5% of the substrate mass, when this kind of condition, the melting point of interesterification product is 27.9℃, the yield is 62%; With sodium methoxide as catalyst, using technology of chemical interesterification to study the effect of temperature, the interesterification time, catalyst amount on the melting point of the product that got from the chemical interesterification of solid fat (which got from dry fractionation) and methyl caprylate, and determine the factors and levels according to single factor orthogonal experiment, get the best process conditions for:interesterification temperature 80 ℃, interesterification time 2 h, the amount of catalyst is 1% of the substrate mass, when this kind of condition, the melting point of interesterification product is 22.4℃, the yield is 82%; with solid fat (which got from dry fractionation) and caprylic acid as substrate,immobilized lipase Lipozyme TL IM as catalyst, a melting point as index to determined the range of some single factor such as lipase, water, substrate ratio, reaction temperature, reaction time,and got best process conditions for acidolysis reaction:the adding quantity is 15%,the substrate ratio of 1:5,acidolysis reaction time of 24 h, acidolysis reaction temperature 50℃, the moisture content of 6%, in this condition, the acidolysis reaction product melting point is 15.9℃,the yield of 85%.To chemical interesterification and enzymatic acidolysis reaction of oil before and after modification for sensory evaluation, the results showed that the oil have the taste of lard, do not have peculiar smell, The color of enzymatic acidolysis reaction proceeds oil is transparent; for the acid value, iodine value, peroxide value and trans fatty acids of modified oil, the determination results shows that the acid value of chemical interesterification and enzymatic acidolysis reaction is 0.52 and 0.84 respectively, the results show that the purification process of the oil is effective;Compared with the dry fractionation solid pig fat, the iodine value of chemical interesterification reaction and enzymatic acidolysis reaction oil decreased to 44.0 and 37.5 respectively, which proves that the caprylic acid was inserted to the modified oil; Peroxide value of the measured values are within the limits prescribed in national standard, no trans fatty acids was determined; Research on fatty acid composition of modified oil suggests that caprylic acid insertion rate of chemical interesterification reaction and enzymatic acidolysis reaction was 26.36% and 39.45% respectively. Palmitic acid content of modified fat was reduced by 7%, stearic acid was reduced by 8% at most, some other fatty acids content all have different degrees of change.Thermodynamic characteristic studies showed that two endothermic peak at -22℃ and 11℃ respectively on the melting curve of enzymatic acidolysis reaction, among them, 11℃ endothermic peak is larger, endothermic peak is 25.6℃ and 15.4℃ respectively on the melting curve of of the chemical interesterification,15.4℃ of endothermic peak is bigger; two exothermic peak of 11.4℃ and 28.1℃ respectively on the crystallization curve of enzymatic acidolysis reaction, among them, the exothermic peak of 11.4℃ is bigger. exothermic peak of chemical interesterification reaction appeared at 0.5℃ and 14.5℃ respectively. Compared with the dry fractionation solid fat pig, chemical interesterification reaction and enzymatic melting endothermic peak of acidolysis reaction and crystallization exothermic peak all move to the direction of low temperature.Rheological characteristics of the study shows that oil viscosity is reduced after modified, under low shear rate, the four kinds of oil samples showed obvious shear thinning of the rheological behavior of non-newtonian fluid, while at higher shear rate range, performance of a Newtonian fluid, the fluid characteristics conform to the Herschel-- Bulkley equation, the correlation coefficient of chemical interesterification and enzymatic acidolysis reaction reached 0.8847 and 0.8847 respectively.