ARTICLE FEED & ADDITIVE MAGAZINE January 2024 57 Non-cellulosic polymers include arabinoxylans, mixed-linked β-glucans, mannans, and xyloglucan while pectic polysaccharides include polygalacturonic acids substituted with arabinan, galactan and arabinogalactan (Table 1). NSPs can be broadly classified into: • Insoluble fibers include cellulose, hemicellulose and pentosans like xylans and arabinoxylans, and • Soluble fibers include mixed linked b-glucans, galactomannan (guar-gum) and pectins. Role of NSPs in fish nutrition The adverse effect of NSP is associated mainly with solubility of NSPs which depends on their chemical nature and their association with the cell wall components and which in turn is responsible for their viscous nature (due to which they do not move easily). Soluble NSPs increases the viscosity, which increases intestinal transit time, delay gastric emptying and glucose absorption, increase pancreatic secretion, and slow absorption. Insoluble fibers are the NSP constituents of the cell wall that shield the substances inside the cell from the effect of the digestive enzymes and thus reduce their digestibility. However, insoluble fibers decrease transit time, enhance water holding capacity of the digesta (chyme), and add to the bulk of faeces in non-ruminant animals. 1. Effect on transit time, feed intake, nutrient digestion and absorption Soluble NSPs bind with the intestinal brush border and increase the thickness of the unstirred water layer adjacent to the mucosa. This increases the viscosity of intestinal content which decreases the intensity of intestinal contractions, which in turn slows down the transit time of the digesta or chyme through the small intestine. Slow passage of digesta through the digestive tract, delays the gastric emptying time which results in reduced feed intake. Due to reduced intestinal peristalsis a certain part of water contained in the chyme forms a hydration sphere Category Monomeric residue Linkage Sources Arabinoxylans Mixed-linked β-glucans Mannans Galactomannans Glucomannans Arabinans Galactans Arabinogalactans (Type I) Arabinogalactans (Type II) Arabinose Galactose Arabinose and Galactose Arabinose and Galactose Cereal co-products Sugar bean meal, sugar-beet pulp Grain legumes Rapeseed cotyledon α-(1→5) β-(1→4) β-(1→4) galactan backbone substituted with 5-linked and terminal arabinose residues β-(1→3,6)-linked galactose polymers associated with 3- or 5-linked arabinose residue Arabinose and Xylose Glucose Mannose Galactose and mannans Glucose and mannans β-(1→ 4)- linked xylose units β-(1→ 3) and β-(1→ 4) β-(1→ 4) β-(1→ 4)-linking mannan chains with α-(1→ 6)-linked galactosyl side groups β-(1→ 4)-linked mannan chain with interspersed glucose residues in the main chain Wheat, rye, barley, oat, rice, sorghum Oat and barley Coffee seed Locust bean gum and guar gum Sugar-beet pulp Cellulose Glucose β-(1→ 4) Most cereals and legumes Table 1. Classification of non-starch polysaccharides Non-cellulosic polymers Non-cellulosic polymers
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