| Docosahexaenoic acid(DHA)is an important polyunsaturated fatty acid for infant brain development.DHA synthesized endogenously by infants is insufficient for their growth and development,so infants mainly consume DHA through diet.Human milk is the most ideal food for infants,with a unique fatty acid composition and distribution.DHA in human milk mainly exists in the form of triacylglycerols(TAGs).However,human milk fat substitute in co mmercial baby food only simulates DHA in human milk fat from the content.No concentration has been paid on the composition and structure of DHA-TAGs in mimetic.In this paper,the composition of DHA-TAGs in human milk fat,animal milk fat and human milk fat substitute were compared.Then,the effects of different fatty acid compositions and structures of DHA-TAGs on the digestion,absorption and accumulation of DHA were explored through mouse experiments.In addition,DHA-rich medium-and long-chain structured lipid were synthesized through two-step reaction catalyzed by lipase.The main conclusions are as follows:First,9 human milk samples of different lactation periods(colostrum,transitional milk and mature milk),4 animal milk powders(milk powder,goat milk powder,sheep milk powder and yak milk powder)and 5 commercial infant formulas were selected.The qualitative and quantitative analysis of DHA-TAGs was carried out by ultra-performance liquid chromatography tandem quadrupole-complex linear ion trap mass spectrometry and ultra-high performance liquid chromatography tandem quadrupole-orbitrap mass spectrometry.40,32 and 20 precursor ions of DHA-TAGs were detected in human milk fat,human milk substitute fat and animal milk fat,respectively,while 90,66 and 37 DHA-TAGs fatty acid isomers were identified.The qualitative results showed that the types of DHA-TAGs in the three kinds of milk fat samples were quite different,and the types of DHA-TAGs in human milk fat were more diverse.The quantitative results showed that the total content of DHA-TAGs in human milk fat was significantly higher than that in other samples(p<0.05),while the distributions of DHA-TAGs in different milk fats were significantly different.Secondly,animal experiments were used to evaluate the effects of different compositions of DHA-TAGs on lipid digestion,absorption and tissue accumulation.The results showed that among the DHA lipids with different compositions,the medium and long-chain DHA transesterified lipids had the highest digestion rate,and its acute intake was beneficial to increase the DHA content in the blood and liver of mice.Meanwhile,when ingested for a long time,it was beneficial to increase the body weight and epididymal fat weight of mice,and to increase the DHA level in the liver and brain.Finally,DHA-rich medium and long-chain triglycerides(MLCTs)were prepared through enzymatic method using DHA algal oil as raw material.The reaction conditions of enzymatic esterification reaction at room temperature were optimized,including lipase species,lipase load,water removal conditions,substrate molar ratio and reaction time.The optimal esterification conditions were as follows:vacuum degree-0.05 Mpa,the molar ratio of monoglyceride to capric acid was 1:3,the lipase load of Lipozyme TL IM lipase was 8 g/g底物,and the reaction time was 9 h.Under the optimal conditions,the lipase has good stability in repeated operation.The total DHA content in the product is 40.04%,the TAGs content is96.55%,and the MLCTs containing DHA account for 67.69%.In conclusion,this paper has accomplished the qualitative,quantitative analysis and comparison of DHA-TAGs in different milk fats,and found that DHA in the form of MLCTs are beneficial to the digestion,absorption and accumulation of DHA by mouse experiments,and successfully synthesized DHA-rich MLCTs through a two-step enzymatic method.The product have the potential to be applied to infant formula and functional foods,and the paper provides theoretical support for the further optimization of DHA additives in infant food. |
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