| Human milk is regarded as the most ideal food for infants. Human milk fat(HMF) accounts for 3%-5% of human milk and supplies the highest fraction(45%) of the infant's required dietary energy as well as the required nutrients. Human milk triacylglycerol(TAG) has a unique structure which is different from those in vegetable oils and animal fats, namely 60%-70% of palmitic acids(C16:0) are located at the sn-2 positions while unsaturated fatty acids are preferentially esterified in the sn-1,3 positions. However, palmitic acids located at the sn-1,3 positions are released as free fatty acids(FFA) which will bind to calcium when present at a high concentration in the intestinal tract and form hardly-soluble calcium soaps which caused loss of energy and calcium, and this could also influence bone mineralization of infants. So the objective of this project was to conduct some studies on development of human milk fat substitutes(HMFS) to enhance fat absorption and to expand its applications in infant formulas.The free fatty acids blend was prepared with soybean oil, butter and coconut oil at 0.5:0.3:0.2 and it had lower C18:0 ratio(0.42%) and higher percentages of short or medium chain fatty acids and long chain unsaturated fatty acids(C12:0, 8.34%; C18:2 and C18:3, 41.37% and 11.54%, respectively).The HMFS was prepared with lard and the free fatty acids blend through enzymatic interesterification catalyzied by Lopozyme TL IM. Single factor test and the RSM method were used to investigate the optimal reaction conditions in this study. The results showed that the best conditions of the reaction were substrate ratio(FFA:lard) 2.2:1, enzyme load(% of substrate) 10.5%, reaction temperature 64℃and reaction time 8h, the resulting product indicated the similar fatty acids composition and distribution to those in human milk fat(C18:0, 12.14%; C18:2, C12:0 and sn-2 C16:0, 18.83%, 3.21% and 62.22%, respectively).The microcapsules containing HMFS were prepared with lactalbumin and malt dextrin as wall materials while monoglyceride was used as emulsifier in order to enhance the antioxidative stability. The optimal formula of microcapsules was determined as follows: the ratio of lactalbumin and malt dextrin is 2:1, the ratio of core material to wall materials was 1:2, emulsion concentration was 20% and the monoglyceride load was 0.3%. In addition, the optimal production conditions of microcapsules were homogenizing pressure 25MPa, inletwind temperature 184℃, outletwind temperature 90℃and the encapsulation ratio of product was 93.02%. Physical and chemical parameters of the microcapsules were also investigated and its water content was 4.27% while its solubility was 91.22%. And its shelf life increased from 91days to 198 days after encapsulation and it showed that encapsulation technology improved its thermal stability greatly. The absorption of HMFS was also assessed through animal experiments and the results showed that compared with lard and reference oil, HMFS(88.21%) seemed to be better absorbed than the other oils and the differences among them were significant(P<0.05). The fatty acids profile of lipids in blood was determined through GC and the results showed that the ratio of C16:0(19.26%) in HMFS group was higher significantly than those in the other two groups which indicated the fat was adsorbed efficiently(P<0.05). The fatty acids profile of lipids in small intestine was also studied. The ratio of C8:0 and C10:0 were 2.32% and 1.33% respectiely, lower significantly than those in the other two groups(P<0.05), which indicated the absorption of short chain fatty acids in HMFS group was higher than the others. The results about the fatty acids profile of lipids in feces showed that C16:0 ratio in Reference oil group(0.12%) was higher than that in the other two groups because of the formation of calcium soaps which was caused by higher percentage of C16:0 in palm oil. However, the C18:1 was absorbed with high-efficiency because significantly less C18:1(1.52%) was found in HMFS group than the other two groups(18.91% and 10.19%, respectively)(P<0.05).A new HMFS was developed in this study with lard and free fatty acids blend through enzymatic interesterification catalyzied by Lopozyme TL IM. The absoption of the HMFS was improved significantly. In addition, the antioxidant stability of HMFS was elevated greatly after encapsulation treatment. This HMFS could not only supply enough energy for infants but also reduce the formation of calcium soaps and then improve the fat absorption when it was added in infant formula. This study will enrich our knowledge about the production of HMFS in large scale through enzymatic interesterification greatly. |
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