ARTICLE 58 FEED & ADDITIVE MAGAZINE January 2024 around the intestinal content such that the digestive enzymes are not able to enter the intestinal lumen and also the mixing of enzymes with the intestinal content decreases. This decreases the efficiency of digestion. As no digestive enzymes exist for the breakdown of cellulose and other NSPs, volatile fatty acids (VFA) like acetate, propionate and butyrate are produced in large amount in the gastrointestinal tract (GIT) by microbial fermentation of carbohydrates and endogenous substrates such as mucus. Such drastic change in gut ecosystem decreases nutrient digestion. Increased viscosity also causes shortening of intestinal villi and decreases their thickness which reduces the intestinal absorption surface area. 2. Effect on nutrient metabolism NSP influence the metabolism and utilisation of dietary nutrients like glucose, lipid, amino acids and minerals. It also affected the distribution of digestive enzymes, gastric emptying rate, nutrients absorption and digestion. • Effect on glucose Diet containing high amount of soluble fiber increases viscosity of intestine content. This lowers the activity of digestive enzymes (like intestinal maltase) on substrate (say, maltose), which in turn reduces the availability of glucose and thus delays the intestinal absorption of glucose. • Effect on lipid and cholesterol level NSPs may bind or entrap bile salts (that cause emulsification of fats), thus reducing their efficiency of solubilizing fats. This disturbs micelle formation, thereby impairing lipid absorption in the GIT. Increased viscosity in the intestine also increases bile acid excretion. As cholesterol is the precursor of bile acids so, it alters the hepatic cholesterol metabolism to provide cholesterol for enhanced bile acid synthesis and thus reduces the cholesterol content in the body (hypocholesterolaemia). • Effect on protein and body growth High fiber content in the diet increases abrasion of the intestinal cells and also increase the secretion of mucin which is compensated by the increase in excretion of endogenous protein or endogenous nitrogen particularly, threonine, this also decreases the utilization of nitrogen. This limits the synthesis of body proteins and thus lowers the efficiency of body growth. • Effect on minerals Components of polysaccharides that interact with minerals include the carboxyl group of uronic acid, carboxyl and hydroxyl groups of phenolic compounds and the surface hydroxyl of cellulose. Moreover, NSP-induced digesta viscosity has been shown to hinder mineral absorption mainly, sodium ions. 3. Effect on gelatinization Fish in general have a limited capacity for carbohydrate utilisation and processing methods, such as gelatinisation, have been reported to improve the nutrient bioavailability to the fish. Gelatinization is a thermal modification process that modifies carbohydrate granules in such a way that their susceptibility to enzymatic action increases, making digestion more complete. Wheat, being the major source of starch, also contains a low amount of NSPs. Arabinoxylan is the main NSP in wheat flour. NSPs due to its water-binding capacity (or hydration process) restricts water availability to the amorphous regions (wheat starch) and thus reduces the temperature within these regions and hinders gelatinization. 4. Purified non-starch polysaccharides as immunostimulants Immunostimulants are chemical substances that activate the generalised immune response system of animals. NSP, such as β-1,3-glucans, acts as an immunostimulant. Supplementation of β-1,3 glucan in diets enhances non-specific cellular defence mechanisms by increasing the number of phagocytes and the bacterial killing activity of macrophages. Mannose units that comprise glucomannans, belong to the category of compounds that adhere to receptors used by pathogenic microbes as the first
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