Itt írjon a(z) Non-starch_Polysaccharides-ról/ről

Non starch polysaccharides as nutritive and anti-nutritive factors and their effects on digestion and growth performance.

NSPs along with oligosaccharides are a category of Non starch carbohydrates (NSCs). NSCs in general include a large number of diverse molecules that are able to affect the gut flora of mainly monogastrics where in some cases the effect is beneficial and in others there is severe inhibition of the digestive process. These changes include changes in the endocrine, immune and dynamic systems of the gut. The digestibility of different NSCs and therefore different NSPs is highly dependent on the animal species in question, the chemical structure of the NSP molecule, its solubility and also the amount of NSP present.

The interest in carbohydrates and NSPs came about due to two separate disciplines being:

• Human nutrition and health: where the role of dietary fibre in the maintenance of gut health is investigated and lowering of energy uptake is most desirable for people eating a high carbohydrate diet.

• Animal nutrition research: where strategies and extrinsic enzymes for minimising anti-nutritive effects of NSP are sought after and enzymes are used to improve the digestibility of NSP to manipulate the fermentation properties of these NSPs and oligosaccharides and their prebiotic effects.

An NSP sturcture found abundantly in wheat, oat, rye and barley is arabinoxylan which is constructed of a polymer chain of β,1-4 linked D-xylose sugars with arabinose substitutions along the polysaccharide chain. The arabinose substitutions make arabinoxylan relatively soluble. The insoluble form can also be found when it has no arabinose substitutions. In the case of oat and barley the main NSPs making up their endosperm cell walls are mixed-link β-glucans which is made up of glucose chains of variable lengths linked at β,1-4 with intermittent β,1-3 links. The β,1-3 side chains have the same effect as the arabinose subsitutions in that these make the whole structure soluble and not allowing the NSP structure to precipitate. (Bedford, 1995)

Most studies conducted are on monogastrics since NSPs do not result in digestive problems in digastric animals. The monogastric species studied most for NSPs and their effects on particular species nutrition nutrition are swine and poultry. This is because the culture of these two species is very much industrialised.

Digestion of NSPs.

Since pigs and poultry have no endogenous enzymes digestion heavily relies on chemical digestion by the acid of the stomach of the pig and crop in the case of the chicken and microbial degradation. Large intestinal microflora in pigs can digest up to 93% of the NSPs ingested but this is not so much in poultry. The cecum is the site of fermentation in the avian gastro intestinal tract and when undigested NSPs and other carbohydrates are transformed into short-chain fatty acids and gases (Józefiak, Rutkowski, & Martin, 2004). A study by Carré et al. (1990) reported that digestion of NSPs in adult birds ranged 21.9% in wheat based diet to 13% in lupin based diet. Therefore NSPs cannot be considered as one entity due to the multitude of factors that their digestion depends on. The digestion of NSCs and therefore NSPs by microflora in the large intestine of pigs can act result in contributing 50% of dietary energy to the pig. In chicken this value is also much lower where energy obtained by fermentation of this material is that of 24kJ per day which is approximately 2-3% of the dietary energy supply. (Choct & Kocher, 2001)

Non starch polysaccharides (NSPs) composed of pentoses and hexoses are the main materials making up plant cell walls in cereal grains and legume seeds used in feedstuffs. These are though not hydrolysed by the digestive enzymes secreted by the digestive system and therefore their more soluble forms tend to produce a viscous mass within the intestinal lumen. This dense viscous mass results in decreased rate of diffusion of substrates and digestive enzymes and hinders interaction at the surface of absorption. This results in inhibited growth. Insoluble NSPs on the other hand can surround endosperm cells and act as an inhibitory coating which digestive enzymes cannot penetrate. (Choct & Kocher, 2001)

Soluble NSPs are more readily digested then insoluble NSPs. In pigs soluble NSPs are nearly completely digested while insoluble NSPs are only 34 to 60% digested. In poultry soluble NSPs is 12.6% digested in middle small intestine and 19.1% digested in the latter part of the small intestine. A study by Carre et al.(1995) though showed that soluble NSPs were 80-90% digested and non-soluble NSPs were not digested at all. The large difference between the digestion of cellulose and pentosans also suggests that not only solubility but also sugar composition of the NSP is highly determinant for its digestion.