Introduction: carbohydrates in foods
Carbohydrates are one of the four major classes of biomolecules and play several important roles in all life forms, including:
● sources of metabolic fuels and energy stores
● structural components of cell walls in plants and of the exoskeleton of arthropods
● parts of RNA and DNA in which ribose and deoxyribose, respectively, are linked by N-glycosidic bonds to purine and pyrimidine bases
● integral features of many proteins and lipids (glycoproteins and glycolipids), especially in cell membranes where they are essential for cell–cell recognition and molecular targeting.
Carbohydrates are very diverse molecules that can be classified by their molecular size (degree of poly-merization or DP) into sugars (DP 1–2), oligosac-charides (DP 3–9), and polysaccharides (DP > 9). The physicochemical properties of carbohydrates and their fates within the body are also influenced by their monosaccharide composition and the type of linkage between sugar residues. Examples of food carbohy-drates and an overview of their digestive fates are given in Table 5.1.
From birth, carbohydrate provides a large part of the energy in human diets, with approximately 40% of the energy in mature breast milk being supplied as lactose. After weaning, carbohydrates are the largest source (40–80%) of the energy in many human diets, with most of this derived from plant material except when milk or milk products containing lactose are consumed. The carbohydrate contents of some vege-table dishes are summarized in Table 5.2.
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