Effects Of Different Freezing And Thawing Manners On Human Milk Properties

Human milk,known as “white blood”,is the gold standard for infant feeding.From the perspective of long-term storage,From the perspective of long-term storage,direct freezing after expressing breast milk is the most suitable treatment for family storage when mothers cannot breastfeed their babies in time.However,there is no consensus on the evaluation and recommendation of frozen-thaw manner for human milk.Therefore,fresh human milk was taken as control in this study.Firstly,the differences of basic components,lipid and protein digestibility under different freezing manners(normal freezing(-18?)and deep cryogenic freezing(-60?))as well as different thawing manners(slow thawing(placing in the air at 4? for 10-hour stationary),medium thawing(placing in the air at 25? for 1-hour stationary)and rapid thawing(shaking in the tepid water at 45? for1 minute))were investigated.The optimal thawing manner was rapid thawing.Then,the changes of basic indicators,lipid and protein properties of human milk were investigated under normal freezing(-18?),deep cryogenic freezing(-60?)and deep cryogenic rapid freezing(-60?(R)).It is expected to provide data support for the use and evaluation of frozen milk,as well as the development of mother-baby refrigerators.The main research contents and results are as follows:(1)Effects of different frozen-thaw manners on the properties of human milk.Results showed that there was no significant difference in the content of fat,protein and bioactive components in human milk under three thawing manners,and the lipase activity was the weakest under the rapid thawing manner.The frozen-thaw processes had effect on lipase activity as well as digestibility of lipid and protein.Rapid frozen-thaw manner(thawing at 45?after freezing at-60?)can reduce the degree of initial lipolysis of human milk,reduce the aggregation of human milk fat globule(HMFG)and protein,which is most conducive to the digestion of lipid and protein,showing the closest quality to fresh human milk.(2)Changes in human milk basic macroscopic under different frozen storage.Results showed that the content of fat and protein,p H,as well as total aerobic bacterial counts of human milk decreased significantly during 180 days storage at-18?,but there was no significant difference between-60? and-60?(R).The content of lactose decreased significantly after 60 days of frozen storage,but there was no significant difference under all frozen storage.(3)Changes in human milk lipid properties under different frozen storage.Results showed that the content of non-esterified fatty acids and lipid peroxide increased significantly during180 d storage at-18?.The content of unsaturated fatty acids decreased after 180 d.During storage,the milk fat globule membrane(MFGM)rupture and lipid accumulation were observed.All kinds of volatile compounds increased significantly,and the off-odor compounds increased,which is related to lipid oxidation and degradation.On the other hand,the content of nonesterified fatty acids and lipid peroxide only increased in a small amount,long chain polyunsaturated fatty acids decreased slightly after 180 days when frozen at-60? and-60?(R).Furthermore,the damage of HMFG was much less in frozen group at-60? and-60?(R)than-18?.With respect to-60? and-60?(R),there was no significant difference between these two groups,but-60?(R)was more effective in maintaining the original flavor of human milk than-60?.(4)Changes in human milk protein properties under different frozen storage.Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that there was no significant difference in high abundance protein under different frozen storage.A total of 1617 proteins were identified and quantified by liquid chromatography and tandem mass spectrometry,and173 significantly differential proteins were found to be related to ribosome,tight junction and neurotrophin signaling pathway.Compared with frozen time,frozen temperature had more obvious effect on serum protein profiles.The serum protein profiles of human milk stored at-18? for 60 days and 180 days was significantly different,which was highly related to the damage of MFGM and transfer of MFGM proteins into whey phase during frozen-thaw process.On the contrary,the serum protein profiles changed little at-60?(R).Human milk frozen at-60?(R)had more advantages in lipid digestion and antioxidant than that at-18?.The active components decreased significantly at-18°C,and this change may be due to ice-induced denaturation.In conclusion,deep cryogenic rapid freezing(-60°C(R))and rapid thawing(45°C water bath shaking)are more conducive to keep the quality of frozen human milk close to fresh human milk in terms of basic index,lipid and protein characteristics,as well as digestibility.