Apart from water, the major constituents of most foods are carbohydrates, proteins and lipids. Irradiation of low molecular weight food carbohydrates, such as glucose, mannose, ribose and lactose results in the formation of low levels of radiolytic products mostly derived from reaction of hydroxyl radicals (OH°), generated from water, with the sugar. A predominant reaction is the oxidation of hydroxyl groups, often with loss of a neighbouring hydroxyl group. Products such as 2-deoxy-gluconolactone and gluconic acid are formed, and the pH value of simple sugar solutions falls (von Sonntag, 1980). Carbohydrates irradiated in the solid state are generally more resistant than those irradiated in solution.
Irradiation of high molecular weight carbohydrates (starch, pectin, cellulose, carrageenans, etc.) sometimes causes major changes in the physical properties of the foods that contain them. Properties such as viscosity, mechanical strength, swelling and solubility are likely to change in such a way as to reduce their functionality in a food, but sometimes change to improve their effectiveness for a particular function.
Irradiation of lignocelluloses, in woody materials, has been shown to increase their subsequent biodegradability by microorganisms such as Flavobacterium species (Bhatt et al, 1992). The limited breakdown that occurs increases their susceptibility to the microorganism's hydrolytic exoenzymes. The properties of gums, such as Karaya gum (Le Cerf et al, 1991) change greatly on irradiation with, for example, very large increases in solubility, falls in viscosity and loss of water-swelling properties.
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