The Investigation Of Transformation And Absorption Of Non- Starch Polysaccharides (NSPs) In Rat’s Gut

Non-starch polysaccharides (NSPs) compose the main components of dietary fibre, which arebelieved to be beneficial for gut health, immune system and cardiovascular system. The structure of NSPs presents a great variety in different plant cell wall. Oat NSPs contain more nearly half of hemicellulose and cellulose while soy NSPs contain half of pectin and 30% of hemicellulose. Up to date, no report describing the digestion and fermentation of NSPs in SD rat model has been founded. In the present research, the oat and soy were used to investigate the transformation and absorption ofNSPs in SD rat model and clarify the exact mechanism in vivo.In our study, rats were fed with three different diets:a) Chow, a basic feed for rats; b) 70% of chow and 30% of oat; c) 70% of chow and 30% soy. Digesta samples were obtained from caecum (Cae) and colon (Col). Above digesta samples were then milled and freeze-dried for further analysis. The a-amylase and amyloglucosidase were used to remove the starch in diet samples for the further NSPs analysis. The monosaccharide composition of feeds and digesta samples were also analysed on gas chromatography by derivation into alditol acetates. HPAEC and HPSEC were applied to investigate the oligo-polysaccharides properties in water soluble and alkali soluble parts of feed and digesta samples. The MALDI-TOF MS was used to investigate the structure of oligomers in alkali soluble parts from digesta samples.The results shows that more than 87% of NSPs of chow and chow+oat diet are composed of arabinose, xylose and glucose. The 94% of monosaccharides in chow+soy diet are arabinose, xylose, galactose, glucose and uronic acid. The ratio of arabinose to xylose was 0.4 in chow+oat diet and then increased to 0.53 in the samples from caecal and remained almost the same in the samples from cecal in chow+oat diet group. The Ara/Xyl ratio of feed and digesta from rats in chow diet group is similar with chow+oat diet group but in a higher value, while the ratio remained around 0.7 in feed and digesta from rats in chow+soy diet group. The similarity of monosaccharides composition and Ara/Xyl ratio during the digestion and fermentation between chow and chow+oat diet group suggested that the NSPs composition of chow is similar with oat, but the structure ofNSPs is different. And the increase of Ara/Xyl ratio from feed and caecal samples from rats in chow and chow+oat diet group indicated that the degradation of arabinoxylan mainly occurred in caecum.After the fractionation using water and alkali, around 50% to 92% of NSPs from feed and digesta samples were recovered. Water soluble fraction of carbohydrates decreased after the digestion and fermentation in guts demonstrated that some NSPs could be fermented and utilized by microbes in the caecum and colon. Around 12% to 24% of carbohydrates in WSS fraction were starch revealing that the rats cannot make use of starch diet completely. The other soluble glucose could be originated from microbes in guts.Different carbohydrates distribution of alkali extracts, along with different mono-sugar composition in 4M ASS fraction of caecal and fecal samples after digestion and fermentation in vivo indicated that NSPs were deconstructed by microbial fermentation. However, the HPAEC results of enzymatically degraded alkali soluble fraction of digesta samples from chow, chow+oat and chow+soy diet group demonstrated that the degradation of NSPs by digestion and fermentation in rats’ gut is not completely. The MALDI-TOF mass spectrometry results showed thatthe backbone of poly-/oligo-saccharide in the 4M ASS degraded fractions from Col samples in Chow diet group were hexose or pentose. However the further analysis is needed for the above results.In general, the NSPs in chow diet is similar to which in oat diet, therefore the chow diet could be considered as an arabinoxylan rich material. The NSPs can be degraded during the digestion and fermentation in rafs gut, and can be utilized. In rats gut, arabinoxylan is more difficult to be fermented than the glucan and pectin. Most of arabinoxylan degradation happens in rat’s ceacum. During the digestion and fermentation in rats gut, the NSPs cannot be degraded completely.The structure of them could be changed, leading to the change of properties, such as solubility.