Polysaccharides least soluble

Generally, reinforcing, cell-wall polysaccharides are least soluble while emollients, mucilaginous, and food reserve polysaccharides represent the most soluble group. Exceptions to the generalization that reserve food polysaccharides are easily soluble occur in starch amylose and seed mannan. Starch amylose is readily dispersible in most of its natural forms since it occurs mixed with easily soluble amylopectin which facilitates the dissolution of the amylose. 

Least Soluble Polysaccharides. As indicated, the most insoluble polysaccharides are those which are reinforcing structural polymers in cell walls. The best example is cellulose, the universal reinforcing struc-... 

With endogeneous pectic polysaccharides as substrates, the pectin methyhransferase activity was measured as radioactivity linked to oxalate-soluble polys x harides after extensive washing of microsomes with IM ethanolic NaCL Figure 2 shows that the rate of methylesterification of pectic substances was maximal on days 4 and 6 these maximum activities were observed within this period in at least five independent ejqjeriments. On the other hand, little activity was noted in young cells before day 2, and in old cells after day 9. In other words during the stationary phase the newly synthesised pectins remained unesterified because of the lack of pectin methyltransferase activity. 

There is also evidence that at least some of the phenolic aldehydes and dehydrodiferulic acid (Figure 1) are linked covalently to cell wall polysaccharides. When ryegrass cell walls were treated with cellulase, the aldehydes and the acid were released as water-soluble carbohydrate-aromatic compounds from which the aromatics were released by cold sodium hydroxide treatment (6,7). This suggests that these compounds are either ether-linked or, in the case of the acid, ester-linked to the polysaccharides. 

Fibre drinks, containing both soluble and insoluble fibres (non-starch polysaccharides). These drinks add bulk to the diet and increase stool weight (a low stool weight is associated with an increased risk of bowel cancer and gall stones). Fibre also binds cholesterol (a risk factor for heart disease), thus reducing its adsorption from the intestine. To support a claim, the quantity of drink consumed in a day must provide at least 3 g of fibre, i.e. one-sixth of the recommended daily allowance of 18 g. 

Difficulties are encountered in carrying out controlled, partial hydrolyses of chitin because of the need to use concentrated acids to dissolve the polysaccharide. Chitosan (de-A -acetylated chitin), however, is water-soluble and amenable to controlled hydrolysis. Using ion-exchange chromatography, a chitosan hydrolyzate has been fractionated to give at least five saccharides, the first two of these having been characterized as 2-amino-2-deoxy-D-glucose hydrochloride and chitobiose hydrochloride. > Fractionation of chitosan hydrolyzates on oarbon-Celite was only successful after selective A-acetylation and then it yielded the first seven members of a series of chitin saccharides, the properties of which clearly indicate the... 

Most polysaccharides used in foods are predominantly hydrophilic and not surface active. Some polysaccharides, however, notably gum arabic, contain minor protein moieties, and do adsorb onto O-W (and presumably A-W) interfaces. By chemical modification, hydrophobic groups can be introduced. The best known examples are cellulose ethers, such as methyl cellulose and hydroxypropyl cellulose, which substances are well soluble in water (at least below 40° C) and strongly surface active. 

The sulphate-rich material could be converted into a sulphate-free charonin by degradation with methanolic hydrogen chloride and this product contained two polysaccharides, one of which was very similar to cellulose by a variety of chemical and biochemical criteria. The other polysaccharide resembled one of the least sulphated and most soluble of the components of the sulphate-poor fraction. This fraction is, anyway, heterogeneous and of uncertain structure, though a 1,4 and some al,6-glucosides appear to be present, as well as a rather small amount of pi,4-glucoside. 

Although there has been much activity to produce totally biodegradable water-soluble polymers for a variety of applications, especially for detergents, few complete successes have been registered beyond poly(vinyl alcohol), poly(ethylene oxides), and poly(aspartic acids). Almost aU efforts to obtain carbon chain polymers that are completely biodegradable have failed, at least in the short-term testing protocols currently in use. Some promising leads are noted in condensation polymers, polyaspartic acids, and acetals and in the modihcation of natural polysaccharides. 

---