| Cocoa butter equivalent (CBE) is a kind of cocoa butter alternatives which is prepared through oil modification techniques. Though it is not made by cocoa beans, it has similar composition of triacylglycerols (TAG) with cocoa butter. According to this property, they share almost the same plasticity and crystallization properties. CBE and CB can miscible with each other in any proportion. With these advantages, CBE shows a wide application in the confectionery industry. Nowadays, with the development of nonaqueous enzymology, synthesis of CBE through enzymatic interesterification has drawn a lot attention. This paper aimed to prepare CBE through enzymatic acidolysis. The process parameters of reaction, the enzymatic mechanism and the performance of product were analyzed in the present study.Firstly, the production of CBE through enzymic acidolysis of palm oil mid-fraction (POMF) with stearic acid (SA) using lipase as a catalyst was analyzed. Factors such as the lipase source, the enzyme–substrate ratio, solvent, the water activity of lipase, the initial mass ratio of POMF/St and the temperature adopted were investigated to analysis their influence on the yield of the acidolysis, the reaction rate and the triglyceride composition in the final product. The optimized acidolysis reaction using POMF and stearic acid (at a mass ratio of 1:2) to produce cocoa butter equivalent was at the cyclohexane system, 60℃, with an immobilized lipase, Lipozyme RM IM (8% enzyme load) which water activity was controlled at 0.55.on this condition, the yield of the reaction can be maintained at more than 92%, and the TAG composition was quite similar with CB.Secondly, the mechanism of this acidolysis reaction has been investigated. Two models were introduced in order to make a more comprehensive understanding of the reaction. For the first model, it was believed that with the participation of lipase, the replacement of palmitoyl group by SA was consistent with the nucleophilic-elimination mechanism. In this reaction, the lipase binds with both substrates to create enzyme-acyl complexes, and at the SAme time, diacylglycerols and water were also generated as byproducts. When the concentration of SA was low(<3.3 mol/L), the model was in good agreement with the experimental values(R>0.98). But as the high concentration of SA (>3.6 mol/L) was used, the fitness of the model declined(R<0.94). The second model adopted the Ping-Pong Bi Bi mechanism to describe the initial rate of the reaction. Nonlinear regression methods were employed to fit experimental data with the proposed models, the kinetic parameters deduced from these models were used to simulate the behavior of the reaction, which were in good agreement with the experimental values. The kinetic parameters of the Ping-Pong Bi Bi were: Vmax=43.18 mmol/(min·L·g),POPK =0.8954 mol/L,Ks =1.4381 mol/L,KiA=4.9381 mol/L。At last, the comparison and analysis of CBE and CB was carried out in six properties. They were hardness, polymorphism, solid fat content (SFC), isothermal crystallization kinetics, non- isothermal crystallization kinetics and crystal morphology. It was found that the hardness of CBE was a little harder than CB. The analysis of XRD showed that CBE trended to have moreβ′crystals thanβ. The SFC test showed that they had similar trend, but at 35℃, CBE had a higher value of SFC(about 7%). The isothermal crystallization kinetics analysis showed that CB and CBE had similar nucleation mechanism at low temperature, but when the higher temperature was used, CBE was more likely to adopt heterogeneous nucleation, which made the performance of SFC different from CB. The non- isothermal crystallization kinetics analysis showed that the main crystallization peak of CB and CBE had similar properties. The crystal morphology was carried out by polarized light microscopy(PLM), it can be seen that the temperature had a big influence on the nucleation mechanism. At high temperature, CB tended to adopt the disc-shaped growth, meanwhile C was more likely to adopt the spherical growth. |
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