Enzymatic Synthesis And Characterization Of Glycerol Monooleate And Its Applications In Low Fat Ice Cream

Three commercial immobilized lipases, Lipozyme RM IM, Lipozyme TL IM and Novozym 435, were screened for the production of GMO (Glycerol monooleate)by glycerolysis of camellia oil in a solvent medium of tert-butyl alcohol. Novozym 435 showed the best performance and was selected to catalyze the subsequent glycerolysis reaction. For the batch reaction, different reaction conditions, substrate mole ratio, substrate concentration and temperature, for the GMO concentration and conversion rate of TAG, were investigated. The optimal reaction conditions were determined as 6:1 mole ratio of glycerol to camellia oil at 40% (w/v) of substrate concentration in tert-butyl alcohol at a reaction temperature of 50℃. Under these optimal conditions, the conversion rate of camellia oil was 98.7% (10 h), and the mixture of acylglycerols contained 82.0% of MAG. A packed-bed reactor (PBR) system with 4.5 g Novozym 435 was employed in continuous production, the resulting product mixture of acylglycerols contained 80.74% of MAG and was obtained at a flow rate of 0.25 mL/min of substrates. The long-term operation of the PBR system gave an average productivity of 0.698 Kg MAG/(Kg enzyme·h) after 38 days of operation.Kinetic study of GMO production by glycerolysis of camellia oil using Novozym 435 has also been investigated, and a mathematical model that took into account for mechanism of glycerolysis reaction using camellia oil as substrate was developed. The kinetic parameters were estimated by fitting experimental data of glycerolysis reaction of camellia oil by Novozym 435 into proposed model equations. There was a good agreement between experimental results and those proposed model predicted equations under conditions of various enzyme, water, glycerol and camellia oil concentrations. From proposed model equations, the synergic effect of glycerol and palm olein concentrations was simulated. The simulation results show that the behavior of high substrate concentrations obtained high initial production rates but low yields of MAG. Thus, with a concentration of 15.27mM of camellia oil and 91.62 mM of glycerol, the concentrations of Novozym 435 and water were 1.09g and 12.15 mM, respectively, the high initial production rate of MAG of 9.733mM·h-1 and corresponding yield of 1.8379 mM MAG·mM-1 TAG were obtained.In this study, molecular distillation (MD) was used to purify GMO synthesized lipase-catalyzed reaction. Orthogonal design was carried out in order to study the effect of operating conditions on the mass ratio (D/F) using MD process to purifying GMO. Among the four studied variables, evaporator temperature (ET), feed flow rate (Q), feed temperature (FT) and condenser temperature (CT), only ET and Q are important at the studied experimental conditions. The model equations of MAG and DAG concentration in the outlet stream to the operating conditions ET and Q was proposed: MAG=-577.41+7.44ET-34.13Q+0.24ET×Q-0.02ET2-5.28Q2; DAG=801.97-8.51ET-1.64Q+0.01ET×Q+0.02ET2-0.16Q2, there was a good agreement between experimental results and those predicted equations. The MAG recovey rate depends strongly on the purity of MAG was desired, GMO with a purity of 80% can be obtained by the operating conditions of Q=0.71ml/min,FT=70℃,CT=60℃,ET 170-190℃, the corresponding recovery rate of GMO is 60-80%. A strategy that consisting of two distillation steps was developed to obtain distilled MAG, Q=1mL min, ET=180℃, FT=90℃, CT=60℃, MAG with a purity of 98.9% can be obtained, the corresponding recovery rate of MAG was 33.42%.Physical and chemical analysis of products indicated that, the GMO synthesized by lipase-catalyzed reaction contain 82.42% of MAG, acid value 4.10, free glycerin 3.21%, hydroxyl value 314, iodine value 78, lead 0.08 mg/kg, residue on ignition 0.03%, saponification value 175 , which met the requirements of FCC-V very well. The fatty acid composition is C12:0, 0.06%; C14:0, 0.08%; C16:0, 10.59%; C16:1, 0.13%; C18:0, 3.36%; C18:1, 73.91%; C18:2, 1.87% and others 3.13%. GMO occurs as a waxy solid at room temperature. It has a mild, fatty taste. It is soluble in hot alcohol and in chloroform; very slightly soluble in cold alcohol, in ether, and petroleum ether; and insoluble in water. It melts at 35-36℃, The hydrophilic-lipophilic balance (HLB) of GMO is 3.7. The storage stability of GMO with added antioxidants BHT, L-ascorbyl palmitate and TBHQ could be significantly improved, the sample with added antioxidants mixed by 0.015% BHT, 0.015% L-ascorbyl palmitate and 0.015% TBHQ had the highest stable degree of 33-36 month guarantee in room temperature, which was 1.38-1.71 times higher than that of control group. In certain sense, GMO used as emulsifier in low fat ice cream was able to compensate for the decrease of sensory quality of low fat GMS ice cream. Unsaturated GMO was more powerful than saturated GMS at displacing caseins from the fat interface and brought more partially coalesced fat to air interface, giving the final product better melting resistance.