Investigation Of The Preparation Of Low-calorie Cocoa Butter By Transesterification Using Immobilized Lipase As Catalyst

As the fatty acid composition and triacylglycerol profile of cocoa butter are significantlydifferent from other fats and oils, its melting point is unique and close to the body temperatureof human. Therefore, chocolates, which contain more than30%of cocoa butter, will bemelted immediately and endow consumers with smooth mouth feel when they are entered intomouth. In food manufacture industry, especially the candy manufacture industry, chocolatewith high calorie and unique favor is one of the most popular sweet foods around the world.In the composition of chocolate, cocoa butter is looked as the main source of high calorie. Thecalorie offered by cocoa butter accounts for more than50%of the total calorie of chocolate.It means that people who need to strictly control the ingestion of high calorie have to reducethe consumption of this high-dense caloric sweet food or completely exclude it from the diet.At present, chocolate industry promising develops with an increasing rate of10-15%peryear, indicating that the market of chocolate has enormous prospects. With more and moreattention focused on healthy diet, there have great potential requirements on low-calorie cocoabutter and low-calorie chocolate. Cocoa butter structured by appropriate approach not onlyhas a lower calorie but also meets the demands of more consumers.The study firstly screened the conditions for preparation of low-calorie cocoa butter bytransesterification using immobilized lipase Lipozyme TL IM as a catalyst in solvent-freesystem. Effects of processing parameters, such as molecular sieve dosage, reactiontemperature, incubation time, enzyme dosage as well as mass ratio of substrates, ontransesterification rate, melting point of low-calorie cocoa butter and contents oftriacylglycerols were also investigated. Three significant processing parameters oftransesterification by immobilized lipase Lipozyme TL IM were optimized by centralcomposite response design. The optimized parameters were that enzyme dosage12U/g,incubation time13h, reaction temperature60°C. Under the optimal parameters mentionedabove, when transesterification between cocoa butter and free fatty acids (mass ratio of cocoabutter, caprylic acid and behenic acid1:0.3:0.1, wt/wt/wt) was catalyzed by immobilizedlipase, the transesterification rate acquired was28.15±2.54%, melting point of low-caloriecocoa butter was36.83±0.55°C.The kinetics of preparation of low-calorie cocoa butter in solvent-free system bytransesterification using immobilized lipase Lipozyme TL IM was studied. The investigationindicated that transesterification by immobilized lipase accorded with ping-pong reaction mechanism. The kinetic model of initial velocity of transesterification between cocoa butter and caprylic acid was the reaction rate constant was0.02928g/mmolmin; The kinetic model of initial velocity of transesterification between cocoa butter and behenic acid was, the reaction rate constant was0.05196g/mmol·min. The kinetic models developed in this study would correctly reflect the relationship between the contents of triacylglycerols in low-calorie cocoa butter and reaction time.The effects of liquid-liquid extraction on refining low-calorie cocoa butter were investigated. The results showed that acid value of refined low-calorie cocoa butter would meet the standard when crude low-calorie cocoa butter was extracted10stages by85%(v/v%) ethanol aqueous solution at35℃with an employment of a mass ratio of1:1crude low-calorie cocoa butter to solvent. Solvent extraction is not well directly applicable to deacidify crude low-calorie cocoa butter with high acidity as a consequence of high solvent consumption and tedious extraction procedure. Therefore, D202anion exchange resin, which has excellent capability of deacidification, was introduced into the deacidification process and united with liquid-liquid extraction. The optimal processing parameters of removal of free fatty acids from low-calorie cocoa butter by D202anion exchange resin were that deacidification temperature was30℃, reaction time was5h, the mass ratio of D202anion exchange resin and crude low-calorie cocoa butter was2:1, the concentration of crude low-calorie cocoa butter/hexane solution was200mg/mL. Acid value of final product achieved the requirement when crude low-calorie cocoa butter was extracted two stages by85%ethanol in successive with the D202anion exchange resin treatment using the optimal parameters.The process of ion exchange adsorption between D202anion exchange resin and free fatty acids in crude low-calorie cocoa butter/hexane solution accorded with Langmuir adsorption isothermal curve. The results of kinetic investigation showed that the main rate determining step was diffusion control of liquid film. The results of thermodynamic investigation demonstrated that ion exchange was an endothermic, spontaneous and entropy-driven process.Molecular distillation was employed for deacidification of crude low-calorie cocoa butter. Acid value and Lovibond color (yellow value and red value) of low-calorie cocoa butter after deacidification were set as responses, the study was carried out to research the effects of evaporation temperature, feed flow rate and pressure, on deacidification rate and quality offinal product. Central composite response design was employed for optimization ofdeacidification parameters of molecular distillation. The optimal parameters were evaporationtemperature185°C, feed flow rate2.3mL/min and pressure1.0Pa. Refined cocoa butter withacid value of2.15±0.23mg KOH/g and Lovibond color of yellow and red values of5.50±0.70and0.60±0.10was acquired when optimum parameters of molecular distillation wereutilized.Caloric availability of low-calorie cocoa butter prepared by transesterification usingimmobilized lipase as a catalyst was estimated by growth method of animal experiment. Thecaloric value of low-calorie cocoa butter was4.70kcal/g and about69%of the caloric valueof cocoa butter. For the experiment of high fat diets, the body weights of Wistar rats fed bylow-calorie cocoa butter did not significantly increase. Moreover, the antioxidant levels andserum lipids levels of experiment group fed by high fat diet of low-calorie cocoa butter wereclose to the corresponding values of normal group fed by normal diet and better than thevalues of control group fed by high fat diet of cocoa butter.The chemical characteristics of low-calorie cocoa butter after deacidification had nodistinguish differences with the characteristics of cocoa butter. The oxidative stability oflow-calorie cocoa butter was evaluated by Schaal method and Rancimat method. The resultsindicated that the oxidative stability of low-calorie cocoa butter was a little weaker than cocoabutter, whereas, its oxidative stability was close to cocoa butter when appropriate amounts ofantioxidants were added into low-calorie cocoa butter. The solid fat contents of low-caloriecocoa butter and cocoa butter were determined by wide-line nuclear magnetic resonance. Theexperimental results suggested that solid fat content of low-calorie cocoa butter was lowerthan cocoa butter and reduced more slowly with temperature increasing. Isothermalcrystallization kinetics of low-calorie cocoa butter was agreed with Avrami equation.