Composition Of Phospholipid,Structure And Low-temperature Storage Property Of Human Milk Fat Globules

In human milk,lipids are present in the form of fat globules.The phospholipid is surrounded outside of triacylglycerols in the form of milk fat globule membrane which maintain the integrity of the emulsion droplets and stability of the emulsion.Phospholipid is 0.4%~1% of total fat content.Phospholipid and the milk fat globules structure are irreplaceable for the healthy growth of infants,and gradually get attention in infant formula industry.Recently,the study of phospholipid was not sysmatic,especially in its changes along with gestational age and lactation period and milk fat globules structure.This paper mainly studied the phospholipid composition and structure of human milk fat globules.The difference of phospholipid and the structure of human milk fat globules between human milk and infant formulas were analyzed.The changes of human milk fat globules during the low-temperature storage were investigated.The main results were as follows:(1)The phospholipid composition and phospholipid fatty acid composition in human milk from different lactation period and gestational age were analyzed.Results indicated that the main phospholipid in human milk were sphingomyelin(SM),phosphatidylcholine(PC),phosphatidylethanolamine(PE),phosphatidylinositol(PI)and phosphatidylserine(PS).SM was the highest phospholipid which accounted for 35.01±3.31%,followed by PE and PC(28.71±2.48% and 28.57±2.61%,respectively),PI and PS were the lowest phospholipids.The content of total phospholipid in term milk was 24.11±3.25 ?mol/100 mL and had no significant difference with preterm human milk(24.57±6.48 ?mol/100 mL)which declined from 27.47±7.38 ?mol/100 mL at 4±3 day to 20.18±4.85 ?mol/100 mL at 90±3 day.The highest fatty acid content was saturated fatty acid(SFA)which accounted for 66.74±3.91% in human milk phospholipids,followed by polyunsaturated fatty acid(PUFA)which accounted for 17.36±2.17% and monounsaturated fatty acid(MUFA)was slightly lower than the content of PUFA.What is more,fatty acids which account for more than 10% were 16:0,18:0,18:1(n-9)and 18:2(n-6).(2)The phospholipid composition and fatty acid composition of 8 infant formulas and 5 mammal milk were analyzed.And a comparability evaluation system was built based on the human milk phospholipid which provided a quantized similarity coefficient to evaluate the difference of phospholipid in different milk.Results showed that: 1)The contents of phospholipid in different infant formulas were 24.60 ?mol/100 mL to 82.30 ?mol/100 mL which were all higher than the content of human milk phospholipid.Main phospholipids were the same with human milk phospholipid,but the proportion of each phospholipid was much different with human milk phospholipid.In infant formulas,PC was the highest phospholipid which accounted for 39.06%~46.79% and was much higher than 28.57% in human milk.Generally,phospholipid in infant formulas have lower SFA(41.72%~64.73%),but higher MUFA(19.25%~27.79%)than human milk.The similarity coefficient of infant formula was the minimum to 36.50 and the highest was only 81.67.2)Phospholipid classes in mammal milk were the same with human milk phospholipid.The content of phospholipid in goat milk was highest which was 52.26±1.08 ?mol/100 mL and followed by cow milk,and both higher than 24.45±5.80 ?mol/100 mL in human milk,but the donkey milk and yak milk have lower phospholipid.PC was the highest in donkey milk which accounted for 48%.In other mammal milk,the highest phospholipid was PE which accounted for about 40%,in other mammal milk,the highest phospholipid was PE which accounted for about 40%.And the content of SM in mammal milk phospholipid was significate lower than that in human milk.Compared with human milk phospholipid in which 16:0 was 34.09%,18:2(n-6)was 11.79% and 18:1(n-9)was 13.03%,the content of 16:0 and 18:2(n-6)were lower while the content of 18:1(n-9)was much higher.As for mammal milk phospholipid,similarity coefficient of cow milk was the highest and was 83.54 for cow milk in Inner Mongolia and 80.32 for cow milk in Wuxi.The lowest similarity coefficient was 76.90 which was donkey milk.(3)Analysed the difference of structure between human milk fat globules and infant formulas by measuring the particle size,potential and microstructure.The results showed that: 1)There had no obvious structure difference between term and preterm milk fat globules.The size of human milk fat globules was about 5 ?m.Potential was about-5.82 mV.The structure was composed by triacylglycerol core and surrounded by phospholipid membrane.2)The size of the infant formulas were between 0.25 ?m to 0.70 ?m.Z-potential were from-16 mV to-13 mV.The infant formulas did not show the similar structure with human milk fat globules.(4)The changes of phospholipid and structure of human milk fat globules during storage at 20°C,4°C,-20°C and-80°C were measured.The results showed that temperature had a significant effect on the phospholipid content and structure of human milk fat globules,and storage at-80°C had minimal effect.Stored under-80°C for 120 days,the degradation rate of phospholipid was 46.2% which was higher than 42.1% of milk fat content,and the degradation rate of PE was the fastest which was 58.3%.Structural changes of human milk fat globules during storage was mainly due to the degradation of phospholipid and the breakdown of the milk fat globule membrane.Part of the inner core triglyceride was released,and number of small fat globules increased.The unstable fat globules aggregated at the ruptured membrane.