Experimental cookery

Pvi O /\ CH CH \ ^ CH— CH Furan -0 H / H \ H / \ \ / HO \ H HO / CH2OH HO.CH^ OH H Beta-fructopyranose o / \ OH H \ H HO / CH2OH OH H Beta-fructofuranose The two structural forms of the sugars are represented by the terms glucopyranose and glucofuranose for glucose, fructopyranose and fructo- furanose for fructose, etc. To avoid confusion of nomenclature, prefixes are added to the terms indicating structural form to differentiate the stereochemical forms (the same chemical and basic structural form but with different spacial arrangements of the hydrogen and h^'droxyl groups). Thus the prefixes alpha-, beta-, gamma-, etc., added to the name of the sugar with the ending denoting the structural form, such as alpha-gluco- pyranose, beta-glucofuranose, definitely identify each sugar. Haworth and his coworkers at Birmingham have worked out in detail the way in which sugar units are united into chains. Haworth states that there are several ways in w^hich two glucose units may be joined through the intermediary of a common oxygen atom. But of the several OH posi- tions available for providing the union of two glucose units, it has been found that the union is formed through the first carbon of one unit and the fourth carbon of the other glucose unit. Maltose is formed, as shown, by the union of two alpha-glucopyranose units. The union of about 30 alpha-glucopyranose units in this manner, according to Haworth forms starch, though all investigators do not agree on the number of glucose units in the starch chain. (See discussion of starch in Chapter XL) Cellulose is composed of many beta-cellobiose units. In a manner similar to that in which maltose is formed, two beta-glucopyranose units form CLASSIFICATION OF THE CARBOHYDRATES 33 HO.CH HO.CH, The union of two a-glucopyranose units gives a-maltose HO.CH, C- /\ H / H -0 \ i;^ \ OH \l C— I H / H J C 1— O- in HO.CH, H / H 1/ C -' \ OH -0 H I OH H /Ah a-maltose beta-cellobiose. Sucrose is composed of one alpha-glucopyranose united through the first carbon to beta-fructopyranose. The disaccharids contain two monosaccharid sugar groups; the poly- saccharids contain many sugar groups. There are also trisaccharids. There is always the possibility that the trisaccharids and some of the other rare sugars may become commercially important, but at the present time they are little used except in scientific w^ork. The common disaccharids found in foods are sucrose, maltose, and lac- tose. Sucrose is composed of one dextrose and one levulose group; maltose is made up of two dextrose groups ; and lactose is composed of one dextrose and one galactose group. Following is a list of the common carbohydrates used in foods. For a complete list a physiological or organic chemistry may be consulted. MONOSACCHARIDS : Dextrose or glucose Levulose or fructose Disaccharids: Sucrose Maltose Lactose POLYSACCHARIDS : Dextrins Starch Cellulose Pectins Gums 34 SUGAR COOKERY Sources o£ the Common Sugars