Nonstarch Polysaccharides NSP

Plant carbohydrates may be divided into three groups as shown in Table 10.1. The non-starch polysaccharides, e.g. cellulose, fall mainly into the third group of structural carbohydrates. (Although the hemicelluloses such as galactans and mannans are associated with the cell-wall, they are termed storage polysaccharides (Graham, 1991), and have been included under the structural category in Table 10.1 for convenience.) They are structural cell-wall carbohydrates associated with the fibre fraction. Although the NDF determination is suitable for members of the Poaceae (= Graminae, grasses, cereals), it underestimates the cell-wall content in legumes. One reason is that legumes and other non-grass species contain relatively high concentrations of pectic polysaccharides that are solubilized by neutral detergent and therefore omitted

Table 10.1. The three main groups of plant carbohydrates with typical examples

and occurrences.

Carbohydrate

Sub-divisions;

group

other descriptions

Examples

Typical occurrence

Soluble sugars

Monosaccharides

Glucose

Plants, fruit

Fructose

Green leaves, fruit

Oligosaccharides

Sucrose (disaccharide)

Sugar beet, carrots

(2-9 monosaccharide Maltose (disaccharide)

Germinating barley

residues)

Raffinose (trisaccharide)

Sugarbeet, molasses,

cotton seed (8%)

Polysaccharides

Fructans (fructosans)

All plant parts of

(soluble storage)

Compositae and

Poaceae; 50% DM in

Jerusalem artichoke

Starches

Storage

Amylose (20-28%)

Seeds, tubers, roots

polysaccharides

(linear molecule) to-

gether with amylopectin

(72-80%) (branched

molecule) (Note: both

are glucosans)

Structural

Non-starch

Cellulose (a glucosan)

Cell-walls, cotton

(including cell wall polysaccharides;

Arabinoxylans (hemi-

Cereals

storage polysac

cell-wall/fibre

celluloses)

charides)

carbohydrates;

p-glucans (glucosans,

Endosperm cell-walls

lignocellulose

mixed-linked)

of barley and oats

Galactans, mannans

Palm kernels, lupin

(hemicelluloses, cell-

seed

wall storage)

Pectins (partially soluble) Dicotyledons

Xylans (hemicelluloses)

Grasses

(Note: hemicelluloses

and pectic substances

are heteropolysaccharides)

from the NDF fraction (Chesson, 2000); some of the hemicellulose fraction is also omitted for the same reason. For hind-gut fermentors, such as equids, the NSP method is also to be preferred, because arabinoxylans, P-glucans, oligosaccharides, and xylans are only fermented in the hind-gut. Different species, or breeds within species, may digest these individual components with varying degrees of efficiency, therefore their individual characterization and estimation would be beneficial in animal nutrition studies.

Starch that escapes amylolytic digestion in the small intestine, together with the oligosaccharides, fructans and NSP, will proceed to the large intestine for fermentation by hind-gut microflora. If present to excess, sufficient lactic acid will be produced to lower the pH in the hind-gut, possibly causing colic or laminitis. Up to about 15% of the NSP has been found to disappear pre-caecally, and is therefore unavailable for microbial breakdown and absorption of nutrients in the lumen of the hind-gut (Moore-Colyer et al., 1997a, b). The determination of the different classes of carbohydrates in the feed will help in the correct formulation of horse rations (Longland, 2001, unpublished).

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