Study On The Preparation Of Milk Fat Substitute By Palm Oil

Milk fat substitute oil is a kind of fat substitute, which is added to infant formula.Currently mixed vegetable oils is mainly used in infant formula. Compared with humanmilk fat, mixed vegetable oils contain the same percentage of palmitic acid and oleicacid, but the fatty acids on the location of the glycerins are different. Palmitic acid inmixed vegetable oils is mainly appeared in the Sn-1,3, while oleic acid is in Sn-2. Thelocation distribution of fatty acids has great influence on the health of the infants.Firstly, four kinds of commercially palm oil with different melting points, fourkinds of infant formula and two types of OPO (1,3-dioleoyl-2-palmitoyl glycerol)products were analyzed about the composition and distribution of fatty acids. Theresults confirmed that:(1) Palmitic acid conten increased with the melting point of palmoil. The content of total palmitic acid content and Sn-2palmitic acid in the fourth kindof palm oil could reach57.32%and30.16%.(2) In four kinds of infant formula andtwo kinds of OPO products, all kinds of total fatty acid content were roughly in thestandard range of breast milk fat, but the percentage of Sn-2palmitic acid in totalpalmitic acid content were40.43%,45.13%,43.25%,45.13%,47.59%and51.15%,which were far away from70%of that in the breast milk fat.Because the content of Sn-2palmitic acid is much less than that in the breast milkfat, in this paper Sn-2palmitic acid in palm oil of four was enriched through fourdifferent ways:(1) The enrichment of Sn-2palmitic acid in palm oil by enzymatic acidtransesterification in solvent system: In solvent system, with the nonspecific lipase ofNovozym435as the catalyst, we chose the fourth kind of palm oil and palm acid foracid transesterification to produce triglycerides rich in palmitic acid at Sn-2position. Bymono-factor experiment, the optimum speed was200r/min and solvent quantity was8mL/g reaction mixture.We also studied the substrate ratio (palmitic acid: palm oil),reaction time, reaction temperature and enzyme load. On the basis of mono-factorexperiment, we carried out the four factors and three levels of response surfaceanalysis.When the content of Sn-2palmitic acid was60%, the optimum conditionswere determined as follows:the quality ratio of palmitic acid and palm oil1.09:1,reaction time9.9h, reaction temperature54.7℃, enzyme load21.9%. Under theoptimized conditions, the content of Sn-2palmitic acid in the product was60.59%.(2) The enrichment of Sn-2palmitic acid in palm oil by enzymatic acidtransesterification in nonsolvent system: In nonsolvent system, with the nonspecific lipase of Novozym435as the catalyst, we chose the fourth kind of palm oil and palmacid for acid transesterification to produce triglycerides rich in palmitic acid at Sn-2position. On the basis of mono-factor experiment, we carried out the three factors andthree levels of response surface analysis. When the content of Sn-2palmitic acid was60%, the optimum conditions were determined as follows: the quality ratio of palmiticacid and palm oil0.36:1, enzyme load16.99%, reaction time12.97h. Under optimizedconditions, the content of Sn-2palmitic acid in the product was60.09%.(3) The enrichment of Sn-2palmitic acid in palm oil by enzymatic intramolecularrearrangement reaction in solvent system: With the nonspecific lipase of Novozym435as the catalyst, we chose the fourth kind of palm oil as raw material to producetriglycerides rich in palmitic acid at Sn-2position under certain conditions by enzymaticintramolecular rearrangement reaction. Through mono-factor experiment, we found thatthe content of Sn-2palmitic acid reached the maximum value when solvent quantitywas4mL/g reaction substrate. When the reaction temperature was60℃, the reactiontime was6h and the enzyme load was10%, the content of Sn-2palmitic acid reached56.20%, which can be used as the interemediate product for the preparation of humanmilk fat substitute in the next step. Under the above conditions, when the using of thenonspecific lipase of Novozym435repeated27times, the loss of enzyme activity was29.44%.(4) The enrichment of Sn-2palmitic acid in palm oil by chemical intramolecularrearrangement reaction in solvent system: With sodium ethoxide as the catalyst, wechose the fourth kind of palm oil for intramolecular rearrangement reaction to producetriglycerides rich in palmitic acid at Sn-2position. We examined the effect of threefactors about reaction temperature, catalyst amount (with palm oil quality meter) andreaction time on the content of Sn-2palmitic acid in triglyceride. The results showedthat reaction time had the minimal impact on intramolecular rearrangement reaction. Atlow reaction temperature, intramolecular rearrangement reaction degree increased withthe increase of catalyst amount.But at high reaction temperature, the effect of catalystamount was weakened. In actual production process, we should choose high catalystamount under low reaction temperature. Optimal conditions about the enrichment oftriglycerides with Sn-2palmitic acid by chemical method were: reaction temperature80℃, sodium ethanol addition amount1.0%and reaction time20min. Under optimizedconditions, the content of Sn-2palmitic acid in the product was58.57%.In solvent system, with Sn-1,3specific lipase of Lipozym TL IM as the catalyst,we chose triglycerides contening Sn-2palmitic acid of56.06%by enzymatic intramolecular rearrangement reaction and oleic acid as intermediate materials, for theoleic acid substitution reaction of Sn-1,3palmitic acid. On the basis of mono-factorexperiment, we carried on the four factors and three levels of response surface analysis.The optimum conditions were determined as follows: quality ratio of oleic acid andtriglyceride contening Sn-2palmitic acid of56.06%3.18:1, reaction time3.5h,reaction temperature48.2℃, enzyme load9.01%. Under optimized conditions, thepalmitic acid content in the fourth kind of palm oil could reach22.95%,while thecontent of Sn-2palmitic acid was48.51%. And Sn-2palmitic acid/total hexadecanoicacid is70.44%.Under the optimum conditions, we carried out the mixing of mixed fatty acid(capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleicacid and linolenic acid). Of the three model experiments, we chose the second model asthe optimum model of preparing human milk fat substitute. Namely, when the massratio of decanoic acid: lauric acid: myristic acid: stearic acid: oleic acid: linoleic acidwas0.5:1:0.75:0.7:10:1, the similarity of the fatty acid composition of human milk fatsubstitute to the selecting human milk fat standard was the highest, getting Sn-2palmitic acid in total palmitic acid was71.13%. In the above reaction conditions, whenthe using of Sn-1,3specific lipase of Lipozym TL IM repeated4times, the loss ofenzyme activity was28.12%.