Camelia W. Soprano, Wyatt, Wayne E., Scaglia, Guillermo, Viator, Sonny | 8/18/2012 1:49:33 AM
In this article:
|Forage-fed Beef Composition: Cholesterol and Fats|
|Forage-fed Beef Composition: Fatty Acids|
Cholesterol and Fats
Contrary to what many people believe, fat and cholesterol are necessary for the human body to function. Cholesterol is found in foods of animal origin (integral part of the cell membrane of animal tissues), so there is no such thing as cholesterol-free beef, poultry or pork. Cholesterol is an integral part of corticosteroids, sex hormones and Vitamin D. There is a group of fatty acids (the “building blocks” of fat) that are essential, which means that our body can’t synthesize them; therefore, we need to consume them in our diet. They are needed to produce many compounds such as prostaglandins among others. We are all aware that blood cholesterol in humans should be below 200 mg/deciliter, but we are also aware that there are two types of cholesterol (wrongly named but popular and easy to understand) which are called lipoproteins: low-density lipoprotein (LDL) and high-density lipoprotein (HDL). The liver is our “processing plant” for cholesterol. Low-density lipoprotein carries cholesterol from the liver to the rest of the body. So if there is too much of it, it will be deposited in the wall of arteries, and this is why it is called “bad” cholesterol. High-density lipoprotein carries cholesterol from the blood back to the liver for elimination from the body and is, therefore, considered “good” cholesterol.
Fatty acids are classified by the number of carbons and the number of double bonds (0, 1, 2 or more), as well as the double bond location and configuration (cis or trans). The main types of fatty acids are: saturated (no double bonds), trans-, monounsaturated (one double bond) and polyunsaturated (more than one double bond). In each of these types there are many different fatty acids. Studies have demonstrated that saturated fats (SFA), as a group, raise total blood cholesterol. However, there is a need for several distinctions: stearic acid (18 carbons, no double bonds) does not elevate blood LDL cholesterol level and is considered neutral. On the other hand, consumption of diets rich in shorter-chain, saturated fatty acids like lauric (12 carbons, no double bonds), myristic (14 carbons, no double bonds) and palmitic (16 carbons, no double bonds) increase blood LDL cholesterol and are considered cholesterol-elevating or hypercholesterolemic.
In the past few years we have heard a lot about use of trans fatty acids and how bad they are for our health (they have a more negative effect on blood cholesterol than saturated fats), reaching the point of being banned from the menus of restaurants in some U.S. cities. They are produced by the hydrogenation (rupture of double into single bonds) of unsaturated vegetable oils and are found in margarines or processed foods. The hydrogenation process increases shelf life. Beef, lamb, cheese, etc. also contain trans-fats, which are naturally produced in the rumen (end product of fermentation process). You may have heard about conjugated linoleic acid (CLA). It is not one fatty acid but a group of them that differ in the position of the double bonds and their configuration. The CLA was found to act as a growth factor, a fat-to-lean repartitioning agent, anticarcinogenic and hypocholesterolaemic and with antiatherogenic properties. The predominant CLA isomer is rumenic acid, which is produced naturally in the rumen representing about 90 % of CLA present in milk and 75 % of CLA present in beef fat. Another major trans-fatty acid in most ruminant products is vaccenic acid (18 carbons, one double bond at carbon 11 with trans configuration), which can be converted (in our cells) to CLA.
Monounsaturated fatty acids (MUFA) contain one double bond. Oleic acid (18 carbons, one double bond at carbon 9 with cis configuration) is the predominant fatty acid in ruminant animal products and comprises from 30-50% of the total fatty acids present. Consumption of diets rich in monounsaturated fatty acids increases good (HDL) and lowers bad (LDL) cholesterol levels.
In recent years the nutritional importance of the omega-3 fatty acids, and the omega-6:omega-3 (n-6:n-3) fatty acid ratio in the human diet has aroused great interest. There is increasing evidence that n-3 polyunsaturated fatty acids (PUFA) play a major role in human health and development. It has been suggested that these fatty acids, specifically eicosapentaenoic acid (20 carbons with five double bonds) and docosahexaenoic acid (22 carbons with six double bonds), are involved in the development of brain and retinal tissues and the progression and prevention of human diseases, including heart disease and some cancers. An increase in the consumption of n-3 fatty acids has been recommended to overcome the imbalance in the ratio of n-6:n-3 PUFA in current diets. Meat, fish, fish oils and eggs are the only significant sources of n-3 PUFA with 20+ carbons for human diets. Meat has lower concentrations of these fatty acids than oily fish. However, since fish consumption is low and beef accounts for an important proportion of the meat in typical U.S. diets, it is important to enhance the levels of these fatty acids in meat.
A study, conducted here at the Iberia Research Station, sought to examine the merits and negatives of introducing “new” genetics (Africaner) into a commercial herd. The research has examined the preweaning, weaning, postweaning, feedlot, carcass and meat quality traits of various crossbred types. This research has also examined the reproductive performance and calf production of first-calf cows (heifers). Two tropically adapted sire breeds, Braford (Brahman-influenced) and Bonsmara (Africaner-influenced), were used on Brangus (Brahman-influenced) cows. Also, Hereford and Bonsmara sires were used on both Angus and Brangus cows. This research has been completed. Reports will be generated for the public in the coming year.
I hope I’ve given you some appreciation for why we conduct crossbreeding research and why we need to do so periodically, given that breeds are always changing in their characteristics. Also, I hope you will look forward with anticipation as I make available the results of our recent crossbreeding research. The LSU AgCenter is always looking for ways in which we might exploit genetic variation in beef cattle in such a way as to provide a better product and for the economic well-being of our cattle producers.
Dr. Wayne Wyatt