Food: The Chemistry of its Components
Chapter 4: Lipids
Published:09 Oct 2015
Food lipids fall into two groups. The non-polar triglycerides predominate in the edible fats and oils, found as energy reserves in plants and animals. The polar lipids (mostly phospholipids) occur in cell membranes but contribute to the structure and behaviour of many foods. Fats and oils have complex melting properties related to their component fatty acids. Cocoa butter, in chocolate, is an extreme example of this complexity. Unsaturated fatty acids react readily with oxygen (with or without the involvement of enzymes) causing rancidity and even polymerisation. Natural and synthetic antioxidants delay the onset of rancidity. Fractionation, hydrogenation and interesterification can be used to convert liquid oils, rich in polyunsaturated fatty acids, into more useful spreading fats, nowadays without the undesirable generation of trans fatty acids). The role of dietary fatty acids in arterial disease remains controversial. Polar lipids, including naturally occurring phospholipids such as those of egg yolk, and synthetic alternatives are extensively used as emulsifiers. The polar lipids of the milk fat globule membrane contribute to the manufacture of cream and butter. Cholesterol and the phytosteroids are other important polar lipids. The chapter includes listings of the antioxidants and emulsifiers permitted as food additives in the EU, USA and elsewhere and concludes with a list of specialist books and review articles for further study.