270 OLIVE OILS AND HEALTH · lipoprotein (a) A lipoprotein produced in the liver and present in blood plasma. It consists of an LDL particle rich in cholesterol, an apolipoprotein B100 molecule, and an additional protein, apolipoprotein (a). Its levels vary widely between individuals, as they are genetically determined. Lipoprotein (a) is a significant risk factor for atherosclerotic disease (myocardial infarction, stroke, and peripheral arterial disease). In addition to promoting atherosclerosis, lipoprotein (a) may contribute to arterial obstruction by forming blood clots, as it acts like a clotting factor. Due to its genetic basis, and unlike other cardiovascular risk factors, lipoprotein (a) cannot be modified through diet or exercise. (see also “Apo E4”, “Apolipoprotein A1” and “Apolipoprotein B”) · plasma lipoproteins Although the term lipoprotein could refer to any association between lipids and proteins, it is commonly restricted to a specific group of molecular complexes found in mammalian blood plasma. The role of plasma lipoproteins is to transport lipid molecules between organs through the aqueous environment of the plasma. They form a polydisperse and heterogeneous system of particles with a roughly spherical shape, consisting of a hydrophobic core (non-water-soluble) made up of non-polar lipids, such as esterified cholesterol and triglycerides, and a hydrophilic surface layer (affinity for water) containing non-esterified cholesterol, phospholipids, and apoproteins. In the normal fasting state, human plasma contains four main types of lipoproteins: Very Low Density Lipoproteins (VLDL), Intermediate Density Lipoproteins (IDL), Low Density Lipoproteins (LDL), lipoprotein (a), and High Density Lipoproteins (HDL). After digestion and absorption of food, a fifth type appears: the chylomicrons. ……………………………………………………………………………………………… - oxidative damage; oxidative deterioration; lipid oxidation; lipid peroxidation; lipid peroxidation chain; peroxide value Lipid peroxidation refers to the oxidative deterioration of lipids (fats, oils, etc.) through the formation of peroxides (oxides that contain higher than normal levels of oxygen), such as hydrogen peroxide (H₂O₂; by contrast, water is H₂O). Polyunsaturated fatty acids are the first and most affected in this process. It can be triggered or accelerated by a range of physical and chemical factors, including direct sunlight, exposure to oxygen in the air, heat, and humidity. Rancidity is one of the most common and concerning consequences of oxidative deterioration. It can occur during the production, storage, transport, or processing of lipid-based products. Oxidative damage not only leads to a loss of quality in fats and the products derived from them (due to unpleasant odours and flavours that reduce their acceptability), but it also results in the formation of toxic substances that may be harmful to health. For these reasons, oxidative deterioration is one of the most closely monitored degradation processes. It is typically controlled through good manufacturing and storage practices, and the addition of antioxidant substances. As mentioned elsewhere in this book and throughout this glossary, the minor components of virgin olive oils are especially rich in antioxidants. Oxidative deterioration can be assessed by measuring the peroxide value.
RkJQdWJsaXNoZXIy Njg1MjYx