Composition, Structure and Absorption of Milk Lipids: A Source of Energy, Fat-Soluble Nutrients and Bioactive Molecules

Milkfat is a remarkable source of energy, fat-soluble nutrients and bioactive lipids for mammals. The composition and content of lipids in milkfat vary widely among mammalian species. Milkfat is not only a source of bioactive lipid components, it also serves as an important delivery medium for nutrients, including the fat-soluble vitamins. Bioactive lipids in milk include triacylglycerides, diacylglycerides, saturated and polyunsaturated fatty acids, and phospholipids. Beneficial activities of milk lipids include anticancer, antimicrobial, anti-inflammatory, and immunosuppression properties. The major mammalian milk that is consumed by humans as a food commodity is that from bovine whose milkfat composition is distinct due to their diet and the presence of a rumen. As a result of these factors bovine milkfat is lower in polyunsaturated fatty acids and higher in saturated fatty acids than human milk, and the consequences of these differences are still being researched. The physical properties of bovine milkfat that result from its composition including its plasticity, make it a highly desirable commodity (butter) and food ingredient. Among the 12 major milk fatty acids, only three (lauric, myristic, and palmitic) have been associated with raising total cholesterol levels in plasma, but their individual effects are variable—both towards raising low-density lipoproteins and raising the level of beneficial high-density lipoproteins. The cholesterol-modifying response of individuals to consuming saturated fats is also variable, and therefore the composition, functions and biological properties of milkfat will need to be re-evaluated as the food marketplace moves increasingly towards more personalized diets.

Keywords:

• bioactive lipids
• conjugated linoleic acid
• lipoproteins
• milkfat
• polyunsaturated fatty acids
• saturated fatty acids

ACKNOWLEDGMENTS

The authors acknowledge the support of Dairy Management, Inc. and the California Dairy Research Foundation.

Notes

^aValues are wt% (see Jensen (2002) for details; adapted from Jensen and Newberg (1995) and National Dairy Council (1993).

^b Bitman and Wood (1990).

^a Adapted from Berner (1993) and Kaylegian and Lindsay (1995).

^b Values are wt%.

^a Values are expressed in mol% for pooled data (n = 55) for mature milk from women in The Netherlands, Caribbean Region, Jerusalem and Tanzania. Modified from Smit et al. (2002). Abbreviations: LC, long-chain; LCP, long-chain polyunsaturated fatty acids; LCSFA, long-chain saturated fatty acids; PUFA, polyunsaturated fatty acids; MCSAFA, medium-chain saturated fatty acids; MUFA, monounsaturated fatty acids; SAFA, saturated fatty acids.

^a Adapted from Piperova et al. (2000).

^b The milkfat-depressing diet was 25% forage and 70% concentrate, supplemented with 5% soybean oil. The control diet was 60% forage and 40% concentrate.