| Human milk is the best food supplied to the infant. Human milk contains 4% fat with more than 98% of this fat in the form of triacylglycerol (TAG) called human milk fat (HMF). HMF provides about the energy and essential fatty acids for the growth and development of infant. HMF contain palmitic acid mainly in the sn-2 position of the glycerol backbone of TAG, while the fat in traditional infant formula milk powder contain palmitic acid mainly in the Sn-1,3 position, which in the baby's digestive process to form calcium soap is not conducive to the baby's absorption of calcium and energy. In contrast, the fat in Sn-2 position of the glycerol backbone is beneficial to the absorption and utilization for infant. At present, inadequate or lack of breast feeding is caused by the pressure of life and other problems, witch makes the infant formula demand increasing. Developing a human milk fat substitute witch fatty acid structure and distribution similar to HMF is particularly important and it has the broad prospects in our country.1. This study compared three commercial immobilized lipase and laboratory self-made lipase to catalyze tripalmitin (PPP) and anhydrous alcohol to synthetize monopalmitin (MPG, including 2-MPG and 1,3-MPG). The alcoholysis reaction conditions were optimized, the optimal conditions obtained by alcoholysis are as follows:Candida sp. 99-125 lipase as a catalyst,15% (w/w PPP) of lipase dosage, PPP/ethanol molar ratio 1:10, ethanol added in seven portions,5 mL/g (acetone/PPP), 45 ?,200 rpm, reaction time of 22 h. Under optimum conditions, the content of MP in reaction mixture increased to 30.08% after 22 h, witch was close to the theoretical value (33%) and the yield was 91.15%.2. Separation and purification of MPG from the alcoholysis reaction was performed by two methods:crystallization and solvent extraction. The optimal crystallization conditions for low temperature solvent crystallization are as follows:20 mL/g of the volume mass ratio of hexane-MTBE solution and reaction product,75:25 of volume ratio of hexane-MTBE, crystal 3 times, each time storage 1 h, storage temperature-25 ?. Under this condition, the purity of MPG was 86.37%, and the yield was 75.79%. The optimal purification condition was obtained by orthogonal experiment of solvent extraction:10 mL/g of the volume mass ratio of hexane and reaction products,15 mL/g of volume mass ratio of ethanol water solution and reaction product,78:22 of ethanol water volume ratio in ethanol aqueous solution. Under this condition, the purity of MPG was 98.01%, and the yield was 78.03%, which was better than that of crystallization.3. The OPO was synthesized by Candida sp.99-125 lipase, and the purified MPG and oleic acid were used as substrates. The effects of the solvent or no solvent system, enzyme dosage, molar ratio of substrates, and the amount of oleic acid supplemented after 1.5 h on the esterification reaction were studied. The optimum condition of the esterification reaction were obtained for no solvent system,9%(w/w total substrate) of lipase amount,1/4 of initial substrate molar ratio of MPG and oleic acid,13.5 mmol oleic acid supplemented after 1.5 h,20% of molecular sieve (w/w, total initial substrate),200 rpm,38 ?,2 h. Under this condition, the yield of OPO was 65.03%,% Sn-2 of palmitic acid was 75.05%, OPO was, and the total triglyceride content was 88.75%, which was almost free of PPP and OOO, and the purity was high. OPO accounted for 88.75% of total triglyceride content, with almost no PPP, OOO and high purity. |
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