| In this thesis, high-acid rice bran oil was chosen as raw material, and enzymaticpreparation of Monoglycerides (MG) in the solvent–free and solvent systems was studied; andthen in the solvent system, with the MG as raw material, enzymatic preparation ofDiglycerides (DG) was studied. Besides, non-isothermal crystallization kinetics of MG wasinvestigated.High acid value rice bran oil (acid value28.45mgKOH/g) was catalyzed by lipase toproduce MG. The reaction of whole system was mainly glycerolysis. Free fatty acid (FFA)esterification and glycerolysis occured simultaneously, but the esterification reaction wasfaster than glycerolysis. Single-factor experiments and orthogonal tests were used to definethe optimum reacting parameters. In the solvent–free system:①Lipozyme435: the bestyield of MG achieved was21.39%under the studied conditions: the amount of substance ratioof rice bran oil to glycerol1:3, enzyme dosage5%(by weight of oil), reaction time8h,reaction temperature80℃.②Lipozyme TL IM: the best yield of MG achieved was11.51%under the studied conditions: the amount of substance ratio of rice bran oil to glycerol1:1,reaction time9h, reaction temperature40℃; enzyme dosage14%(by weight of oil).③The combination of Lipozyme TL IM and Lipozyme435: the best yield of MG achieved was20.71%under the studied conditions: the amount of substance ratio of rice bran oil to glycerol1:3, reaction time7h, enzyme dosage6%(by weight of oil), reaction temperature80℃, TLIM/435ratio3:2(total enzyme by weight of oil6%). With the same enzyme dosage, thedifference of productive rate of MG was pretty small comparing with dual enzymes systemand individual lipase reaction, which indicating that the synergistic effects of dual enzymeswere evaluated by the comparison of the experimental observation of individual lipasereaction system (the2.3section, the best sing-factor experiment MG19.38%) and systemwith a mixture of two enzymes. In addition, the cost of production decreased. In the solventsystem, Lipozyme435: the best yield of MG achieved was66.82%under the studiedconditions: the amount of substance ratio of rice bran oil to glycerol1:6, the ratio of rice branoil to tert-Butanol1:2(m/v), reaction time6h, reaction temperature50℃; enzyme dosage14%(by weight of oil). After molecular distillation of mixture, the purity of MG reached98.56%.In the solvent system, the optimum process conditions for preparetion of DG by enzyme-catalyzed reaction of MG using Lipozyme RM IM were obtained by single-factorexperiments and response surface methodology. The best yield of DG achieved was74.08%under the conditions: reaction time4h, n-hexane to MG5:1(v/m), reaction temperature52℃,enzyme dosage14.7%(by weight of MG). After molecular distillation of mixture, the contentof DG reached87.03%and TG11.99%, which met the requirement of DG oil.Differential Scanning Calorimetry (DSC) was used to study the non-isothermalcrystallization kinetics of MG. The results indicated that crystallization exothermic peak ofMG was double peaks. With the decrease of cooling rate, the time cost for crystallization waslonger and crystallization peaks shifted towards the higher temperature direction withreduction of crystallization at high temperature crystallization peak and increase ofcrystallization at low temperature crystallization peak. However, the total amount ofcrystallization is increasing. Non-isothermal crystallization activation energy of MG wasobtained by the Takhor equation and Kissinger equation, the activation energy of hightemperature crystallization was-246.74kJ/mol and-251.64kJ/mol, respectively; theactivation energy of low temperature crystallization was-99.30kJ/mol and-103.63kJ/mol,respectively. And the mechanism of non-isothermal crystallization kinetics of MG wasinvestigated by using the Mo. method, the a value of high temperature crystallization peakobtained by Mo. method was from1.43to1.90and the F(T) was from0.77to1.28; the avalue of low temperature crystallization peak was from1.20to1.50and the F(T) was from1.12to1.60. |
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