The Fatty Acids Composition And In Vitro Digestion Of Preterm Milk

Triglyceride(TAG)is one of the most important nutrients in preterm milk,but its composition,structure and digestion characteristics are still unclear.This paper aims to elucidate the composition and positional distribution of fatty acids in preterm milk TAG,as well as to clarify the in vitro digestion process of breast milk fat in preterm infant.First of all,there is currently no direct detection method for the sn-3 fatty acids.Based on the sn-3 position specificity of rabbit gastric lipase(RGL),this study established a method for the detection of sn-3 fatty acids in breast milk TAG.RGL was extracted and purified from rabbit stomach,and the specific enzyme activity of RGL was 5.5 U/mg.Considering hydrolysis rate 4% as the reaction endpoint,the optimal measurement conditions for the determination of sn-3 fatty acids were: pH 4.0,substrate mass/enzyme activity=1 mg/5 U,30 min reaction time.Secondly,the composition of total,sn-2 and sn-3 fatty acids of preterm milk in Wuxi region were analyzed by gas chromatography.We found that: 1)The main fatty acids were C16:0,C18:1n-9 and C18:2n-6,which accounted for 21.21%~29.68%,20.21%~27.63% and 14.32%~18.76% of the total fatty acids,respectively;2)C14:0,C15:0,C16:0 and C22:6n-3 are mainly distributed in sn-2 position,whereas C20:3n-6 was mainly located at sn-3 position;3)the content of C18:2n-6 and C20:4n-6 in total fatty acids,C18:2n-6,C18:3n-3,C20:4n-6 and C22:6n-3 in sn-2 position,as well as C20:4n-6 in sn-3 position changed significantly with the development of lactation;4)the relative content of C18:3n-3 and C20:4n-6 in total fatty acids varied significantly owing to gestational age.Thirdly,multivariate analysis methods were used to explore the effect of maternal physiological parameters on the fatty acids composition of preterm milk.We concluded that: 1)long chain saturated fatty acids(LCSFAs)and monounsaturated fatty acids(MUFAs)were much lower(p<0.001)whereas medium chain fatty acids(MCSFAs)were much higher(p<0.001)in colostrum compared to transitional milk;2)MUFAs,LCSFAs,and n-6 family long chain polyunsaturated fatty acids(PUFAs)were higher in early preterm milk compared to moderate preterm and near term milk(p<0.01);3)C18:3n-3(p<0.05)and C22:6n-3(p<0.05)in sn-2 position were lower in preterm colostrum from women aged over 30.Finally,an in vitro gastric-intestinal digestive dynamic model was established to study the digestion characteristics of milk fat.The results showed that the milk fat was slowly digested in the stomach of preterm infant with 6.92%±0.28% digestibility rate(2 hours after feeding),however,lipolysis rate was greatly higher in the small intestine with 39.02%±2.46% digestibility rate(2 hours after feeding).The free fatty acids released during the whole process were mainly C18:1n-9,C18:2n-6 and C16:0,the fatty acids composition of 2-monoglycerides released in the small intestine were mainly C16:0,C14:0,C18:1n-9 and C18: 2n-6.In conclusion,this study preliminarily clarified the composition,structure and digestion characteristics of preterm milk TAG,which provided an important theoretical basis for the further study of lipid nutrition for preterm infant and the development of specialized milk fat.