A number of enzymes may be used as digestive aids (Table 12.9). In some instances, a single enzymatic activity is utilized, whereas other preparations contain multiple enzyme activities. These enzyme preparations may be used to supplement normal digestive activity, or to confer upon an individual a new digestive capability.
ENZYMES OF THERAPEUTIC VALUE Table 12.9 Enzymes that are used as digestive aids
Application a-Amylase Cellulase a-Galactosidase Lactase
Papain Pepsin Bromelain Pancreatin
Aids in digestion of starch
Promotes partial digestion of cellulose
Promotes degradation of flatulence factors
Counteracts lactose intolerance
Enhanced degradation of dietary protein
Enhanced degradation of dietary carbohydrate, fat and protein
The use of enzymes as digestive aids is only applied under specific medical circumstances. Some medical conditions (e.g. cystic fibrosis) can result in compromised digestive function due to insufficient production/secretion of endogenous digestive enzymes. Digestive enzyme preparations are often formulated in powder (particularly tablet) form, and are recommended to be taken orally immediately prior, or during, meals. As the product never enters the blood stream, the product purity need not be as stringent as enzymes (or other proteins) administered intravenously. Most digestive enzymes are, at best, semi-pure preparations.
In some instances there is a possibility that the efficacy of these preparations may be compromised by conditions associated with the digestive tract. Most function at pH values approaching neutrality. They would thus display activity possibly in saliva and particularly in the small intestine. However, the acidic conditions of the stomach (where the pH can be below 1.5) may denature some of these enzymes. Furthermore, the ingested enzymes would also be exposed to endogenous proteolytic activities associated with the stomach and small intestine. Some of these difficulties, however, may be at least partially overcome by formulating the product as a tablet coated with an acid-resistant film to protect the enzyme as it passes through the stomach.
Pancreatin is a pancreatic extract usually obtained from the pancrease of slaughterhouse animals. It contains a mixture of enzymes, principally amylase, protease and lipase, and, thus, exhibits a broad digestive capability. It is administered orally mainly for the treatment of pancreatic insufficiency caused by cystic fibrosis or pancreatitis. As it is sensitive to stomach acid, it must be administered in high doses or, more usually, as enteric-coated granules or capsules that may be taken directly or sprinkled upon the food prior to its ingestion. Individual digestive activities, such as papain, pepsin or bromelains (proteases), or a-amylase are sometimes used in place of pancreatin.
Cellulase is not produced in the human digestive system. Cellulolytic enzyme preparations obtained from A. niger or other fungal sources are available, and it is thought that their ingestion may improve overall digestion, particularly in relation to high-fibre diets.
a-Galactosides are oligosaccharides present in plant matter, particularly in beans. They are not normally degraded in the human digestive tract due to the absence of an appropriate endogenous digestive enzyme (i.e. an a-galactosidase). However, upon their entry into the large intestine, these oligosaccharides are degraded by microbial al-6 galactosidases, thus stimulating microbial fermentation. The end-products of fermentation include volatile fatty acids, carbon dioxide, methane and hydrogen, which lead to flatulence. This can be avoided by minimizing dietary intake of food containing a-galactosides. Another approach entails the simultaneous ingestion of tablets containing a-galactosidase activity. If these 'flatulence factors' are degraded before or upon reaching the small intestine, then the monosaccharides released will be absorbed and, hence, will be subsequently unavailable to promote undesirable microbial fermentations in the large intestine.
Lactose Galactose Glucose
(O-ß -D-galactopyranosyl (1^4) ß-D-glucopyranose) (ß-D-Galactopyranose) (ß-D-glucopyranose)
Figure 12.17 Hydrolysis of lactose by lactase (P-galactosidase)
Lactose, the major disaccharide present in milk, is composed of a molecule of glucose linked via a glycosidic bond to a molecule of galactose. The digestive tract of young (suckling) animals generally produces significant quantities of the enzyme P-galactosidase (lactase), which catalyses the hydrolysis of lactose, releasing the constituent monosaccharides (Figure 12.17). This is a prerequisite to their subsequent absorption.
The digestive tracts of many adult human populations, however, produce little or no lactase, rendering these individuals lactose intolerant. This is particularly common in Asia, Africa, Latin America and the Middle East. It severely curtails the ability of these people to drink milk without feeling ill. In the absence of sufficient endogenous digestive lactase activity, milk lactose is not absorbed and, thus, serves as a carbon source for intestinal microorganisms. The resultant production of lactic acid, CO2 and other gases causes gastrointestinal irritation and diarrhoea. A number of approaches have been adopted in an effort to circumvent this problem. Most involve the application of microbial lactase enzymes. In some instances, the enzyme has been immobilized in a column format, such that passage of milk through the column results in lactose hydrolysis. Free lactase has also been added to milk immediately prior to its bottling, so that lactose hydrolysis can slowly occur prior to its eventual consumption (i.e. during transport and storage).
Fungal and other microbial lactase preparations have also been formulated into tablet form, or sold in powder form. These can be ingested immediately prior to the consumption of milk or lactose-containing milk products, or can be sprinkled over the food before eating it. Such lactose preparations are available in supermarkets in many parts of the world.
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