Biochemistry and Metabolism
Lipids Approximately 35-40% of the total calories taken by an average adult comes in the form of dietary lipids. Oxidation of lipids is well studied by chemists because this reaction is related to lipid deterioration and the production of undesirable breakdown products. Crystalline properties of fats are important in formulations of ice creams, margarines, mayonnaise, and many other common food products. Hydrogenation of lipids is important in the food industry because degree of unsaturation is directly proportional to rate of oxidation. A study of emulsification of fats leads to studies in numerous areas of chemistry: crystal polymorphism, sufrace tension, van der Waals attraction, electrostatic repulsion, electric double layers, adsorption at interfaces, liquid crystals, complex formation.
Proteins The basic chemistry of proteins is always related to their functionality. For example, the chemistry of muscle contraction is related to rigor mortis and postmortem tenderness of meat. The unfolding and refolding of the helical chains in collagen help explain formation of gelatins. Chemical changes in proteins during food storage and processing can lead to unwanted breaddown products, with consequent alteration of nutritional quality.
Carbohydrates--Monosaccharides and Oligosaccharides The many flavor compounds in foods are the result of the degradation and subsequent rearrangements and reactions of monosaccharides and oligosaccharides. The reaction mechanisms of these reactions have been extensively studied. Polysaccharides are important in food chemistry because of their unique gelling characteristics. Gelling of polysaccharides often requires complexation with metal ions, and the degree and nature of the substituent groups also plays an important role.
Vitamins and Minerals Vitamins are essential for the proper functioning of the body. They cannot be biosynthesized by human beings and therefore must be part of the diet. About a dozen different vitamins have been identified, two-thirds of which are water-soluble and one-third of which are fat-soluble. The water-soluble vitamins wash out through the action of the body's aqueous disposal system, and thus must be included in the daily diet. On the other hand, the fat-soluble vitamins can be stored in teh adipose tissues and can leach into the blood stream as needed. In fact, the fat-soluble vitamins tend to accumulate, sometimes to toxically high levels if ingested in excess. Essential minerals can be divided for convenience into macrominerals (Ca, Cl, Mg, Na, K, P and S) and trace minerals (Cr, Co, Cu, F, I, Fe, Mn, Mo, Ni, Se and Zn). All are essential in the diet and lead to deficiency conditions if lacking or in short supply in the diet. ChemCom (2nd ed.) provides an excellent section on vitamins and minerals including a Vitamin C laboratory activity. See ChemCom (1993) in the References. (Idea contributed by Angie Matamoros.)
Kitchen Chemistry Kneading dough is a chemical reaction. During kneading and subsequent resting periods, disulfide bonds in the wheat protein, which is 80% gluten, undergo reduction and subsequent reoxidation. The initiation of reduction in dough-mixing is thought to be due to thiol-disulfide exchange and possible formation of free radicals. Disulfide reduction physically loosens the gluten and facilitates better interaction with the starch, lipids and other additives to form a continuous network complex.
Fertilizers Because of fertilizer losses in the field, energy requirements and environmental concerns, alternative sources of ammonia are being explored. Technology is being developed to make more efficient use of fertilizers, particularly nitrogen fertilizers to control nitrification so that nutrients can be made available to plants on a need-supply schedule (see Industrial Inorganic Chemistry module).
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