Donald L. Palmquist1,2
The Ohio State University Department of Animal Sciences
Introduction
Milk fat has suffered a negative image for many years because it has been portrayed as a heart-unhealthy saturated fat (Havel, 1997). We will discuss that later. First, in order to explain how milk fat may have a role in healthy diets, we need to discuss aspects of its synthesis and composition. Milk fat is a very complex substance, which has caused it to be both a fascinating and productive research subject for many scientists. More than 400 different fatty acids have been identified as components of milk fat; theoretically these could be incorporated into 64 million different molecules in the triacylglycerol (triglyceride) structure. However, because the enzymes responsible for milk fat synthesis place fatty acids on specific positions of the glycerol backbone, the total is much less than 64 million. Nevertheless, the number of different glyceride molecules is great and not one glyceride species constitutes more than a few percent of the total fat (Jensen and Newburg, 1995). Certainly not all the different structures have been identified.
There are four main reasons for the intense amount of research on milk fat composition: 1) historically, fat was the most valuable component of milk; 2) manipulating milk fat composition is useful to scientists who study nutrition and metabolism of the cow because it contributes to understanding regulation of milk fat synthesis and mammary metabolism; 3) milk fatty acid composition and glyceride structure contribute greatly to melting point and plasticity of milk fat, physical properties which are of great importance to the milk processing industry; and 4) as noted above, milk fat composition has become an issue in human nutrition and health.
Recent research has shown that several milk fat components have important anti-cancer activities (Parodi, 1997). These components conjugated linoleic acid (CLA), sphingomeyelin, butyric acid, and glycerol ethers have caused a renewed interest and increased research in milk fat synthesis and composition. It is likely that other components in milk fat remain to be identified as having important health and biological effects.
1For more information, contact at: 312 Gerlaugh
Hall, 1680 Madison Avenue, Wooster, OH 44691-4096,
(330) 263-3795, (330) 263-3949 FAX, Email: palmquist.1@osu.edu
2Presented at a symposium honoring Dr. Stuart Patton
for fifty years of research. Pennsylvania State
University, State College, PA, August 11-12, 2000.