【作者】 李丹；

【导师】 韦伟；

【作者基本信息】 江南大学 ， 食品科学与工程， 2023， 硕士

【摘要】 鞘磷脂(SM)是广泛存在于细胞膜中的脂类,也是母乳中重要的极性脂质,含量约占总磷脂的40%,在婴儿的生长发育中发挥重要的生理功能,但是分子结构和消化特性尚缺乏深入研究。本实验室前期建立了乳中极性脂的定性定量方法,在此基础上,本研究分析了母乳中SM组成,明确了乳脂肪球膜上SM的流动性并进一步研究了SM体外消化特性。主要研究内容如下:首先,采用超高效超临界流体色谱串联四级杆飞行时间质谱(UPSFC-Q-TOF-MS)分析了三个哺乳期的共90例母乳样本中SM组成和分布特点。结果表明,母乳中的SM主要分布在乳脂肪球和外泌体的膜上,在成熟乳中的含量分别为2.38±1.23 mg/100 m L和1.84±0.7 mg/100 m L,且都不受到哺乳期的影响。总SM中55%分布在乳脂肪球,45%分布在外泌体。在母乳中共鉴定出30种SM分子,脂肪酰基主要为长链饱和脂肪酸,鞘氨醇长链碱基主要为18:1。SM分子在乳脂肪球与外泌体上的分布有明显差异,SM(d18:1/24:1)主要分布在乳脂肪球,SM(d18:1/24:0)主要分布在外泌体。外泌体极性脂及SM脂肪酸的饱和度均高于乳脂肪球。其次,使用多种显微镜技术表征了乳脂肪球和外泌体的微观结构,采用光漂白后荧光恢复技术(FRAP)分析了母乳脂肪球生物分子的流动性。结果表明,外泌体为粒径分布在10～210 nm,平均粒径为144.23±39.42 nm的双层膜结构;乳脂肪球为粒径分布在1～15μm,平均粒径为4～6μm由乳脂肪球膜包裹甘油三酯核心的球状结构。乳脂肪球中的SM主要分布在乳脂肪球膜上,SM在所有生物分子中流动性最慢,其流动分数、半衰期时间以及扩散系数分别为4.85±1.77%、1.89±1.34 s和0.088±0.007 1/s。最后,构建模拟婴儿胃肠道的体外鞘磷脂消化模型,探究母乳和婴配粉SM的体外消化特性。结果表明,婴配粉含有的SM含量因其配料成分和生产工艺的不同而有所差异。SM含量在胃相中偶有波动但保持稳定,在肠相中含量开始下降,最终消化程度为0.00%～15.81%。SM整体消化程度较低,添加大豆磷脂的婴配粉SM结构松散更易被水解,而具有磷脂包裹的大粒径乳脂肪球婴配粉其SM消化程度与母乳相近。母乳与婴配粉总磷脂消化程度为47.98%～65.79%,其中母乳总磷脂消化程度最低,说明母乳具有更强的抵抗磷脂消化的能力。当婴配粉中含有乳脂肪球膜结构或者婴配粉乳脂肪球结构接近于母乳时,其总磷脂的消化程度与母乳更为相近。综上,本研究分析了母乳中SM的分布和含量,测定了SM在乳脂肪球膜上的流动特性,进一步探究了母乳SM体外消化特性,为开发模拟母乳极性脂的婴配粉奠定理论基础。更多还原

【Abstract】 Sphingomyelin(SM)is a lipid widely present in cell membranes,which is also an important polar lipid in human milk.SM accounts for about 40% of the total phospholipids in human milk which plays an important role in the growth and development of infants.However,its structure and digestive properties are still lack of in-depth study.The laboratory established a qualitative and quantitative method for polar lipids in milk in the early stage.On this basis,this study analyzed the composition of SM in human milk,clarified the fluidity of SM on the human milk fat globule membrane,and further studied on the in vitro digestion characteristics of SM.The main research contents are as follows:Firstly,the ultra-high performance supercritical fluid chromatography tandem quadrupole time-of-flight mass spectrometry(UPSFC-Q-TOF-MS)was used to analyze the composition of SM in 90 human milk samples from three lactational periods.The results showed that SM was mainly distributed on the membrane of human milk fat globule and exosome,and the contents in mature milk were 2.38±1.23 mg/100 m L and 1.84±0.70 mg/100 m L,respectively,and were stable with lactation period.About 55% of the total SM was distributed in human milk fat globule,and 45% was in exosome.A total of 30 SM molecules were identified in human milk,the fatty acyl groups were mainly long chain saturated fatty acids,and the long chain bases of sphingosine were mainly 18:1.The molecular differences of SM between human milk fat globule and exosome were obviously,SM(d18:1/24:1)was mainly distributed in human milk fat globule,and SM(d18:1/24:0)was mainly distributed in exosome.The degree of saturation of polar lipids and SM fatty acids in exosome was higher than human milk fat globule.Secondly,the microstructural structure of human milk fat globule and exosome was characterized using a variety of microscopy techniques,and the fluidity of human milk fat globule biomolecules was analyzed using fluorescence recovery after photobleaching(FRAP).The results showed that exosome was a double layer membrane structure with a particle size distribution of 10～210 nm and an average particle size of 144.23±39.42 nm;human milk fat globule was a spherical structure with a particle size distribution of 1～15 μm and an average particle size of 4～6 μm,with the triglyceride core wrapped by human milk fat globule membrane.SM was the slowest mobile of all biomolecules.The mobile fraction,half life time and diffusion coefficient of SM mainly distributed on the membrane of human milk fat globule were 4.85±1.77 %,1.89±1.34 s and 0.088±0.007 1/s,respectively.Finally,an in vitro SM digestion model was constructed to simulate the gastrointestinal tract of infants,and explored the in vitro digestion characteristics of human milk and infant formulas of SM.The results showed that the contents of SM in infant formulas were different due to the difference in ingredients and production process.The content of SM fluctuated occasionally but remained stable in gastric phase,and the content began to decrease in intestinal phase,the final digestibility was 0.00%～15.81%.The overall digestibility of SM was low.The SM structure added with soybean phospholipids was loose and easily hydrolyzed,while the SM digestibility of infant formula with large particle size milk fat globules wrapped by phospholipids was similar to human milk.The digestibility of total phospholipids in human milk and infant formulas was 47.98%～65.79%,and the degree of digestibility in total phospholipids in human milk was the lowest,indicated that the human milk had a stronger ability to resist phospholipid digestion.Infant formula contained milk fat globule membrane structure or infant formula milk fat globule structure was close to human milk,the degree of digestion of its total phospholipids was closer to human milk.In summary,this study analyzed the distribution and content of SM in human milk,measured the flow characteristics of SM on human milk fat globule membrane,and further explored the in vitro digestion characteristics of SM in human milk,which can lay atheoretical basis for the development of infant formula that simulates the polar lipids of human milk.更多还原