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Effect of ultrasonication, lyophilization, freezing and storage on lipids and immune components of human milk

University of British Columbia

Administration of expressed human milk (EHM) to ill and premature infants necessitates tube feeding the babies using mechanical pumps or gravity flow. Tube feeding however, leads to separation and adhesion of milk fat to the tube walls and syringes causing incomplete delivery of fat to the baby. 'Ultrasonic Homogenization' dramatically prevents this fat separation and observed fat loss during tube delivery of milk. However, would the effect of ultrasonication persist after storage? Also, since ultrasonication leads to disruption of large molecules in milk, would the unique nutritional and immune properties of milk be subsequently comprised? There is so far no documentation on the above aspects. This study was designed to determine the effects of ultrasonic homogenization and storage on the following constituents of human milk; 1) free fatty acid (FFA) and peroxide levels, 2) fatty acid profile (FAP), 3) immunoglobulin A (IgA) levels and 4) recovery of fat and protein after infusion. The study was divided into four parts, In part 1, seven EHM samples wer obtained. Each sample was divided into three parts (Pasteurized, Ul-trasonicated, and Ultrasonicated after Pasteurization) and stored in both frozen and lyophilized forms for one and four months. Analysis of Variance (ANOVA) and further Scheffe's tests were performed on the FFA and peroxide data obtained both before and after storage. The levels of FFA rose signficantly (P < 0.01) in the non-pasteurized, ultrasonicated samples and the increase was higher with a longer storage time and lyophilized form of storage. Peroxide levels signficantly increased after storage (P < 0.001), however, the level of increase in the non-pasteurized ultrasonicated group was significantly lower (P < 0.05) compared to the pasteurized groups with or without ultrasonication. In part 2 of the study; five EHM samples were analyzed for FAP both before and after storage in fresh frozen, ultrasonicated frozen and ultrasonicated lyophilized forms for 1 month. Results of Multiple Analysis of Variance (MANOVA) showed a significant decrease in the saturated fatty acids C12:0 and C18:0 (P < 0.001), and Long Chain Poly-Unsaturated Fatty Acids (LC-PUFA) C20:4n6 and C22:4n6 (P < 0.001) with ultrasonication and storage. The levels of C20:5n3 signficantly increased (P < 0.05), and the levels of essential fatty acids Cl8:2n6 and Cl8:3n3 remained unaffected with processing and storage. In part 3 of the study; seven EHM samples were analyzed for IgA in fresh, ultrasonicated and subsequently stored fractions (for 1 month in both frozen and lyophilized forms). Results of paired t tests indicated slight but signficant losses of IgA with ultrasonication (P < 0.05) and subsequent storage (P < 0.01). Losses were higher with lyophilized storage, however, the absolute amount of loss was still small (6.4%) compared to 33% loss reported with pasteurization. In part 4 of the study, eight EHM samples were obtained. Each sample was pasteurized, ultrasonicated and stored in both frozen and lyophilized forms for one and four months. Slow and rapid infusion of milk using mechanical pump and gravity flow was conducted after storage. Fat and protein recovery in the infusates was studied. Milk stored frozen after ultrasonic homogenization resulted in negligible and insignificant loss of both fat and protein upon infusion. However, recovery of fat in the lyophilized milk was signficantly affected (P < 0.01). Lyophilization somehow appeared to reverse the effects of ultrasonication, resulting in fat globules with larger and varied sizes. On the other hand, ultrasonication of lyophilized milk just before infusion, resulted in much more stable delivery of both fat and protein. In conclusion, although ultrasonication and subsequent storage of milk results in slight loss of IgA and some LC-PUFA, these losses don't appear important when considering the possibility of massive loss of fat (and therefore energy) upon infusion of non-ultrasonicated milk. Moreover, the increased FFA levels after ultrasonication and storage could have beneficial implications for the newborn. Also, the antioxidant effects of ultrasonication on peroxide levels of pasteurized milk appears important.

Text

2010-08-16

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http://hdl.handle.net/2429/27414

Human Nutrition

University of British Columbia

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