CARBOHYDRATES 



63 



tract. Since no cellulose-digesting enzyme is known to be secreted by 

 these animals, it is assumed that the hydrolysis is brought about by the 

 action of bacteria. The products formed by such bacteria — acids, or 

 possibly even glucose — may be absorbed and thus serve as sources of 

 energy to the animal. Although cellulose is of no importance to man 

 as a source of energ>', its presence in the digestive tract may serve a 

 useful purpose in giving bulk to the food and may assist in the elimina- 

 tion of food residues. However, there is considerable difference of opinion 

 regarding the value of bulk in the diet. 



On complete hydrolysis pure cellulose gives only glucose. Soft woods 

 (spruce, pine, fir, etc.) give about 50 per cent of glucose and about 10 

 per cent of xylose and other sugars. However, it is not practicable to 

 make glucose from wood and other cellulosic materials because of the 

 difficulties encountered in purifying the sugar. In Europe, wood sugar 

 solutions are fermented for production of ethyl alcohol and yeast on a 

 commercial scale. Such liquors have also been evaporated and used 

 as feed for cattle. 



Fructosans 



Polysaccharides that upon hydrolysis yield fructose are reported to 

 be fairly widespread in plants. Eight fairly well-defined members of 

 this group of polysaccharides have been described. The best known 

 are inulin and the bacterial levari produced by Bacillus subtilis. Inulin 

 consists of about 30 D-fructose residues linked from carbon 2 of one residue 

 to 1 of the next. It is abundant in the roots of the Jerusalem artichoke, 

 dahlia, sunflower, dandelion, and many other plants. The amount varies 

 with the season of the year. It has been proposed that inulin be manu- 

 factured from the Jerusalem artichoke, since this plant produces a very 

 large tonnage per acre, and that the inulin be converted into levulose 

 by acid hydrolysis. However, up to the present time this process has 

 not been attempted on a commercial scale. 



Inulin is a white powder readily soluble in hot water but only slightly 

 soluble in cold water. It gives no color with iodine solution and is 

 easily hydrolyzed with dilute acids. It is not acted upon by diastase, 

 ptyalin, amylopsin, or any known body enzyme. It is not fermented 

 by ordinary yeast, but is easily broken down by many bacteria. 



The bacterial levan of B. subtilis is similar to inulin in its properties, 

 but is made up of D-fructose residues united at the 2 and 6 positions. 



Galactans 



Anhydrides of the sugar, galactose, are known as galactans. They are 

 frequently found in combination with arabinose as a double compound, 



