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Module 4: Nutrient Composition

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Fatty acids

The fatty acid composition of plants depends on climatic conditions and the genetics of the plant. These fatty acids are found as both storage oils and membrane lipids, such as glycolipids, phospholipids and lipoproteins. This section will discuss genetic changes that have been made to change the fatty acid profile in various plants.

Polyunsaturated fatty acids

Polyunsaturated fatty acids (PUFAs) have been found to be important to human nutrition. One of the reasons for their importance is their hypocholesterolemic property related to heart disease. They are also involved in many biological processes in both structural and functional roles as parts of cell membranes, regulators of membrane permeability as well as proteins within the membrane. PUFAs are also involved in gene expression regulation, including genes that provide the information for fatty-acid synthesis, sodium-channel proteins, and cholesterol-7-alpha-hydroxylase. As a result of their part in gene expression, PUFAs impact cellular biochemical activities, transport processes involving lipid metabolism, immune responses, cold adaptation, and conditions such as carcinogenesis and cardiovascular disease (6)

Polyunsaturated fatty acids can be obtained from plant seeds, marine fish and certain mammals. It has been reported that the market for PUFAs may increase, resulting in the need for alternative sources of fatty acids (4). Genetic modifications could help provide alternative sources of these fatty acids and to provide a desirable PUFA profile to meet specific nutritional demands (6).

Trans fatty acids

Trans fatty acid consumption has been regarded as a possible risk factor for coronary heart disease. While most fatty acids are present in nature in a cis configuration (changes the shape of the molecule), trans fatty acids are created when plant oils are hydrogenated.

The concern about trans fatty acids can be overcome by the use of desaturase genes from plants (6). One example of such a gene is the Omega 6 desaturase gene from soybeans. This desaturase inserts a second double bond into oleic acid, making it polyunsaturated. Researchers have used this gene’s activity to suppress the existing gene’s activity. In other words, the addition of the second double bond is blocked. When the second double bond is not added, the result is a monounsaturated oil with no trans fatty acids created during hydrogenation (7).

Canola Oil

Canola oil developed from rapeseed was one of the first examples of nutrition concerns influencing oil seed crop developments (3). That modification was accomplished with traditional plant breeding, however now genetic methods provide a technique to make more specific modifications to plants’ fatty acid biosynthesis pathways (3). These biosynthesis pathways are controlled by multiple genes in plants, with some of the genes controlling fatty acids in specific tissues, which allows for changes that can be made in seed storage lipids (3).

Replacement of high saturated fat oils with less saturated ones is an area of research with human health implications. One example is high laurate canola oil (lauric acid is a medium chain fatty acid) created by inserting the 12:0 thioesterase gene from Umbellaria californica into canola. The benefit of the high amount of lauric acid is that the product can replace the high saturated fat tropical oils that are used in nondairy coffee whiteners and whipped toppings, as well as in confectionery products (1).

Vegetable Oil

There have been several developments used to change the fatty acid profile of vegetable oil. The first genetic modification used cyanobacterial desaturase introduction into the plant. The desaturase introduces a double bond into 16-chain and 18-chain saturated fatty acids which, if expressed in the seeds, the saturated fatty acid content of the oil could be reduced (7). The second modification uses delta 6 desaturase that introduces a double bond into linoleic acid. Linoleic acid is then converted into gamma-linoleic acid, the beneficial compound found in fish oils (7).

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