Polysaccharide maltose

Other disaccharides are the product of the breakdown of larger polysaccharides. Maltose, cellobiose, and isomaltose are all composed of glucose residues (see Figure 2). Maltose and isomaltose both contain a-glucoses in a(l—>4) linkages in the case of maltose, and in a(l—>6) linkages in the case of isomaltose. Maltose results from the hydrolysis of starch, and isomaltose from the hydrolysis of dextrans. Cellobiose is composed of /3-glucose oc-... 

Glucose and fructose (CeHijOj, monosaccharides) sucrose maltose and lactose (CiaHja n, disaccharides) starchy (CaHiflOs), a polysaccharide. 

Carbohydrates may be divided into monosaccharides, disaccharides and polysaccharides. The monosaccharides under certain conditions react as polyhydroxy-aldehydes or polyhydroxy-ketones two important representatives are glucose CjHjjO (an aldose) and fructose (laevulose) CgHuO, (a ketose). Upon hydrolysis di- and polysaccharides 3deld ultimately monosaccharides. Common disaccharides are sucrose, lactose and maltose (all of molecular formula C,2H2. 0,), whilst starch, dextrin and cellulose, (CjHjoOj), in which n > 4, are typical polysaccharides. 

Although glucose can exist as a simple sugar, it is most often found in nature in combined form, as a disaccharide or polysaccharide. Several glucose-containing disaccharides are known. We will consider two of these, maltose and sucrose. 

Carbohydrates are classified based upon the products formed when they are hydrolyzed. Monosaccharides are simple sugars that cannot be broken down into simpler sugars upon hydrolysis. Examples of monosaccharides are glucose, ribose, deoxyribose, and fructose. Disaccharides contain two monosaccharide units and yield two monosaccharides upon hydrolysis. Examples of disaccharides are lactose, maltose, and sucrose. Polysaccharides are polymers of monosaccharide units and yield many individual monosaccharides upon hydrolysis. Examples of polysaccharides are starch, glycogen, and cellulose. 

Saliva begins the process of chemical digestion with salivary amylase. This enzyme splits starch molecules into fragments. Specifically, polysaccharides, or starches, are broken down into maltose, a disaccharide consisting of two glucose molecules. Salivary amylase may account for up to 75% of starch digestion before it is denatured by gastric acid in the stomach. 

Polysaccharide (starch) Amylase Fragment polysaccharides into disaccharides (maltose) Salivary glands pancreas Mouth stomach small intestine... 

A. Abbadi, K. F. Gotlieb, and H. van Bekkum, Study on solid acid catalyzed hydrolysis of maltose and related polysaccharides, Starch, 50 (1998) 23-28. 

Fischer then examined the lactose yeast in the same manner as he did the Frohberg yeast and found it to contain both an invertin-like enzyme and a lactose-cleaving enzyme, which he termed lactase. From these results he concluded that the first step in the fermentation of lactose, as for the fermentation of sucrose and maltose, is the hydrolysis of the disaccharide to mono-sacharide. From this observation, he drew the landmark conclusion that he considered it most unlikely that any polysaccharide (the term included di-saccharides) can be fermented without first being hydrolyzed to hexose (31). 

Maltose from maltose, glucose, polysaccharides Dealuminated Y Water [231]... 

The hydrolysis of cellulose, a polysaccharide, sometimes yields the disaccharide cellobiose. When cellobiose, a reducing sugar, is hydrolyzed, two glucose molecules result. Unlike maltose, which we describe in the preceding section, the linkage involves the (3 anomer of the left glucose (see Figure 16-24). 

Enzymes are also added to catalyze the hydrolysis or saccharification of starch. Malt produced by the germination of barley grain contains the enzymes that catalyze this hydrolysis. Sometimes called diastase, the enzymes are primarily a- and 6-amylase. Glucoamylase is a pure enzyme that can now be used. Both diastase and glucoamylase hydrolyze starch polysaccharide to the disaccharide, maltose. For fuel grade ethanol production, hydrolysis takes place at temperatures ranging from about 120°F to 140°F (50°C to 60°C) for about 1 hour. The final product of hydrolysis is called a wort. Solids can be filtered from the wort before continuing. 

Problem 22.36 Cellobiose, isolated from the polysaccharide cellulose, has the same chemistry as maltose except that it is hydrolyzed by emulsin. Give the structure of this disaccharide. ... 

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