Abstract

Introduction

Materials & Methods

Results

Discussion & Conclusion

References

Discussion
Board

Milk fat consisting of about 98% triglycerides is secreted by the mammary gland as membrane-bound fat globules (MFGM). Milk fat is partly hydrolysed during in-vitro storage predominantly by the action of the serum-stimulated lipoprotein lipase (LPL) (Bitman et al, 1983; Neville et al, 1991). The other type of lipase present in human breast-milk (HBM) is bile-salt-stimulated lipase (BSSL) (Dupuy et al, 1991). The released milk free fatty acids (FFA) have been shown to be able to kill intestinal parasites-Giardia lamblia and Entamoeba histolytica (Rohrer et al, 1986, Hernell et al, 1986), enveloped viruses and bacteria (Kabara & Vrable, 1977; Isaacs et al, 1986). After screening over 40 natural or synthetic lipophilic compounds were screened for anti-microbial activity, Gram (+) bacteria and yeasts but not Gram (-) bacteria were found to be most susceptible (Kabara & Vrable, 1977). Their cytolytic effects on normal white and red blood cells have also been described (Sakaguchi et al, 1995). The cis-unsaturated FFA are the main mediators of this cytolytic effect, with less contribution by lysophosphatidylcholine and monoglycerides, but not diglycerides, phosphatidylcholine, triolein or glycerol. These cytotoxic fatty acids have been shown to be released relatively early during the storage process (Lavine & Clark, 1987).

Though small quantities of bile salts are present in the breast-milk, they are generally not adequate to activate the BSSL before the milk gets into the small intestine of the nursing infant. Serum-stimulated lipoprotein lipase (LPL) is similar to the lipoprotein lipase in the serum. It is present in high activity in the lactating mammary gland where it facilitates the uptake of triglycerides and fatty acids from the blood lipoproteins for the production of milk lipids. The activity in the milk probably represents a leakage of the enzyme from the mammary gland (Olivecrona & Hernell, 1976).

The rate of increase in the level of FFA released from the lipolysis of the milk triglycerides has been characterized. It depends on the temperature and duration of storage, and not on the total lipid content, during the first 48 hours at +4°C storage. 3 to 6 hours of storage at 37°C, 6 to 24 hours at +4°C, and 12 to 24 hours at -20°C are required for the activation of the milk LPL-induced lipolysis (Sakaguchi et al, 1995).

The physiologic significance of in-vitro lipolysis have been called to question, since FFA are equally present in HBM as well as artificial milk formulas, and the latter provide no protection to the nursing infant, in any proportion to that of the former (Isaacs et al, 1990). Few studies have been conducted to investigate the underlying mechanisms and kinetics of the lipolysis-induced cytolysis. This would assist in formulating appropriate storage techniques for HBM. It is necessary to minimize the toxic effects of FFA on the living milk cells, because they represent an essential source of immunological mechanisms in human breast-milk (HBM). Rabbit erythrocytes were employed in this study to assess some of the characteristics of lipolysis-induced cytolysis.

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