Orx

layer at the surface with the carboxyl end in contact with water and the hydrocarbon extending out of the water. The fatty acids may form a micelle (Figure 4) to separate the oil and water phases. These orientations of fatty acids and more complex lipids are a primary aspect of their participation in biological structures and functions. Furthermore, there is free rotation about the carbon-carbon bonds so the fatty acids and acylglycerols are capable of assuming a number of configurations.

Differences in the physical characteristics of fatty acids, particularly saturated compared with unsatu-rated, are extremely important in food and nutrition. SFAs with a chain length longer than 12 carbons are solid at usual ambient temperatures. As the chain lengthens, the melting point increases.

On the contrary, mono- and polyunsaturated fatty acids (PUFAs) are liquid at room temperatures. Uses of fats in food products are based on these properties. Salad oils, margarines, and shortenings are examples of such differences. Hydrogenation of oils containing PUFAs was introduced to provide food fats that are resistant to rancidity and of a desirable plasticity. The chemical hydrogenation process yields mixtures of cis and trans fatty acids (Figure 5). The physical conformation of trans fatty acids is important for their functions in foods and nutrition (Figure 3). The melting points are similar to those of SFAs of similar length and their shapes are linear rather than bent as forced by the cis configuration. These physical characteristics affect their space-filling functions and the mobility of the molecule.

Water

Figure 4 Micelle formed by oil dispersion in water.

Water

Figure 4 Micelle formed by oil dispersion in water.

CH3(CH2)n-CH=CH—C — CH=CH—C—CH=CH—(CH2)nCOOH

Polyunsaturated fatty acid

H2 (hydrogénation) Ni (catalyst)

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