272 OLIVE OILS AND HEALTH · diacylglycerides or diglycerides Formed by the union (esterification) of a glycerol molecule with two fatty acids. They are precursors of triacylglycerides. · triacylglycerides or triglycerides or triacylglycerols Also known as neutral fats, they are formed by the union (esterification) of a glycerol molecule with three fatty acids. They store excess energy from the diet. High levels of triglycerides in the blood, combined with high levels of LDL cholesterol (“bad”) or low levels of HDL cholesterol (“good”), are associated with the accumulation of fat deposits in the arterial walls, which increases the risk of cardiovascular and cerebrovascular disease. ………………………………………………………………………………………… - phospholipids Phospholipids are lipids composed of an alcohol molecule (either glycerol (phosphoglycerides) or sphingosine (sphingolipids) to which two fatty acids (one normally polyunsaturated) and a phosphate group are attached. The phosphate group is also linked to other molecules such as serine, choline, inositol, or ethanolamine. Phospholipids have a polar (hydrophilic) region, where the phosphate group and its associated molecules are located, and a non-polar (hydrophobic) region where the fatty acids are found. They are the main lipid components of biological membranes, where they form bilayer structures. In these bilayers, the non-polar regions are oriented towards the interior, minimising contact with water, while the polar heads face outward towards the surrounding water, where they can interact with protein molecules. PHASE Transition Pahse Transition Low Temerature Gel Like Fluid Like Phase Transition High Temerature cell membrane lipid bilayer NON-POLAR ZONES POLAR ZONES The most abundant phospholipids are phosphatidylethanolamines (or cephalins), phosphatidylinositols, phosphatidic acids, phosphatidylcholines (or lecithins), and phosphatidylserines. The structure of the fatty acids bound to these molecules varies between different phospholipids, hence the use of the plural. For example, in phosphatidylcholine, the fatty acid at position 2 is usually unsaturated, while the one at position 1 is saturated. In phosphatidylethanolamine, the opposite is often the case. As phospholipids are part of cell membranes, they are present in most foods that contain cellular material. Their relevance in food science lies in the fact that, being polar lipids, they tend to orient themselves at the interface between water and hydrophobic substances, helping to reduce surface tension. As a result, they are widely used as emulsifiers and stabilisers in the food industry. The most commonly used phospholipids (lecithins) are typically obtained from refined soybean oil.
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