What are avaiilable and non available carbohydrates in terms of maintaining good health
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Carbohydrates are polyhydroxy aldehydes, ketones, alcohols, acids, their simple derivatives and their polymers having linkages of the acetal type. They may be classified according to their degree of polymerization and may be divided initially into three principal groups, namely sugars, oligosaccharides and polysaccharides (see Figure 1).
Figure 1
The major dietary carbohdrates
Class (DP*)
Sub-Group
Components
Sugars (1-2)
Monosaccharides
Glucose, galactose, fructose
Disaccharides
Sucrose, lactose, trehalose
Polyols
Sorbitol, mannitol
Oligosaccharides (3-9)
Malto-oligosaccharides
Maltodextrins
Other oligosaccharides
Raffinose, stachyose, fructo-oligosaccharides
Polisaccharides (>9)
Starch
Amylose, amylopectin, modified starches
Non-starch polisaccharides
Cellulose, hemicellulose, pectins, hydrocolloids
DP * = Degree of polymerization
Each of these three groups may be subdivided on the basis of the monosaccharide composition of the individual carbohydrates. Sugars comprise monosaccharides, disaccharides and polyols (sugar alcohols); oligosaccharides include malto-oligosaccharides, principally those occurring from the hydrolysis of starch, and other oligosaccharides, e.g. a -galactosides (raffinose, stachyose etc.) and fructo-oligosaccharides; the final group are the polysaccharides which may be divided into starch (a -glucans) and non-starch polysaccharides of which the major components are the polysaccharides of the plant cell wall such as cellulose, hemicellulose and pectin (2,3,4).
Total carbohydrate
Although the individual components of dietary carbohydrate are readily identifiable, there is some confusion as to what comprises total carbohydrate as reported in food tables. Two principal measures of total carbohydrate are used, firstly, that derived by "difference" and secondly the direct measurement of the individual components which are then combined to give a total. Calculating carbohydrates by "difference" has been used since the turn of the century. The protein, fat, ash and moisture content of a food are determined, subtracted from the total weight of the food and the remainder, or "difference", is considered to be carbohydrate. There are, however, a number of problems with this approach to total carbohydrate analysis in that the "by difference" figure includes a number of non-carbohydrate components such as lignin, organic acids, tannins, waxes, and some Maillard products. In addition to this error, it combines all of the analytical errors from the other analyses. Finally, a single global figure for carbohydrates in food is uninformative because it fails to identify the many types of carbohydrates in a food and thus to allow some understanding of the potential physiological properties of those carbohydrates (5,6).
Figure 1
The major dietary carbohdrates
Class (DP*)
Sub-Group
Components
Sugars (1-2)
Monosaccharides
Glucose, galactose, fructose
Disaccharides
Sucrose, lactose, trehalose
Polyols
Sorbitol, mannitol
Oligosaccharides (3-9)
Malto-oligosaccharides
Maltodextrins
Other oligosaccharides
Raffinose, stachyose, fructo-oligosaccharides
Polisaccharides (>9)
Starch
Amylose, amylopectin, modified starches
Non-starch polisaccharides
Cellulose, hemicellulose, pectins, hydrocolloids
DP * = Degree of polymerization
Each of these three groups may be subdivided on the basis of the monosaccharide composition of the individual carbohydrates. Sugars comprise monosaccharides, disaccharides and polyols (sugar alcohols); oligosaccharides include malto-oligosaccharides, principally those occurring from the hydrolysis of starch, and other oligosaccharides, e.g. a -galactosides (raffinose, stachyose etc.) and fructo-oligosaccharides; the final group are the polysaccharides which may be divided into starch (a -glucans) and non-starch polysaccharides of which the major components are the polysaccharides of the plant cell wall such as cellulose, hemicellulose and pectin (2,3,4).
Total carbohydrate
Although the individual components of dietary carbohydrate are readily identifiable, there is some confusion as to what comprises total carbohydrate as reported in food tables. Two principal measures of total carbohydrate are used, firstly, that derived by "difference" and secondly the direct measurement of the individual components which are then combined to give a total. Calculating carbohydrates by "difference" has been used since the turn of the century. The protein, fat, ash and moisture content of a food are determined, subtracted from the total weight of the food and the remainder, or "difference", is considered to be carbohydrate. There are, however, a number of problems with this approach to total carbohydrate analysis in that the "by difference" figure includes a number of non-carbohydrate components such as lignin, organic acids, tannins, waxes, and some Maillard products. In addition to this error, it combines all of the analytical errors from the other analyses. Finally, a single global figure for carbohydrates in food is uninformative because it fails to identify the many types of carbohydrates in a food and thus to allow some understanding of the potential physiological properties of those carbohydrates (5,6).
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