Radical Formation in the Radiolysis of Starch and Lipid-Containing Starch

Abstract

Carbohydrates are the major components of many foods, and their diversity of structure is matched by their diversity of function. They have been traditionally categorized into simple sugars and polysaccharides: The former are used for their sweetening power, preservative action, and crystallinity, whereas the latter confer body, texture, and colloid properties. The polysaccharides, consisting of monoglycerides bound to each other by glycosidic linkages, include cellulose, collagen, glucans, alginates, pectin, and starch. Of the different carbohydrates, the functional properties of starch in food are very much related to its interactions with other components, particularly lipids. In cereals, two types of lipids are generally recognized: surface and internal lipids (i.e., lipids extractable only by polar solvents after gelatinization of starch). Analysis of the surface lipids of wheat and maize starches shows significant qualitative differences from the internal lipids (Galliard and Bowler 1987). Triglycerides are, presumably, derived from the oil storage bodies (spherosomes) that occur in the different tissues of cereal grain. A clear distinction among potato, maize, and wheat starches can be made on the basis of internal lipids. First, of all starch granules, those of maize and wheat contain significant amounts of internal lipids, whereas starch granules from potato and other tubers (e.g., cassava) as well as from legume seeds (e.g., peas, beans) do not contain this type of internal lipids. On the other hand, the significance of the monoacyl character of starch internal lipids (Galliard and Bowler 1987) lies in the fact that these can form helical inclusion complexes with amylose, whereas dior triacyl lipids do not form such complexes. But the presence of lipids also can give rise to anomalous values for the amylose content of starch if this is determined by the conventional I2-binding method because the lipid occupies the same site within amylose helices as those available to iodine in lipid-free amylose, leading to apparent values of 21.4 instead of 27.5 in the case of maize, and 20.4 instead of 27.2 in the case of wheat (Galliard and Bowler 1987). Consequently, lipids often alter rheological properties of cereal starches (Colonna et al. 1987). If present on the surface of starch granules, lipids may affect