Resistant starch (RS) is starch and products of its small intestinal digestion that enter the large bowel. It occurs for various reasons including chemical structure, cooking of food, chemical modification, and food mastication. Human colonic bacteria ferment RS and nonstarch polysaccharides (NSP; major components of dietary fiber) to short-chain fatty acids (SCFA), mainly acetate, propionate, and butyrate. SCFA stimulate colonic blood flow and fluid and electrolyte uptake. Butyrate is a preferred substrate for colonocytes and appears to promote a normal phenotype in these cells. Fermentation of some RS types favors butyrate production. Measurement of colonic fermentation in humans is difficult, and indirect measures (e.g., fecal samples) or animal models have been used. Of the latter, rodents appear to be of limited value, and pigs or dogs are preferable. RS is less effective than NSP in stool bulking, but epidemiological data suggest that it is more protective against colorectal cancer, possibly via butyrate. RS is a prebiotic, but knowledge of its other interactions with the microflora is limited. The contribution of RS to fermentation and colonic physiology seems to be greater than that of NSP. However, the lack of a generally accepted analytical procedure that accommodates the major influences on RS means this is yet to be established.

Short-Chain Fatty Acids and Human Colonic Function: Roles of Resistant Starch and Nonstarch Polysaccharides

Saponins are steroid or triterpenoid glycosides, common in a large number of plants and plant products that are important in human and animal nutrition. Several biological effects have been ascribed to saponins. Extensive research has been carried out into the membrane-permeabilising, immunostimulant, hypocholesterolaemic and anticarcinogenic properties of saponins and they have also been found to significantly affect growth, feed intake and reproduction in animals. These structurally diverse compounds have also been observed to kill protozoans and molluscs, to be antioxidants, to impair the digestion of protein and the uptake of vitamins and minerals in the gut, to cause hypoglycaemia, and to act as antifungal and antiviral agents. These compounds can thus affect animals in a host of different ways both positive and negative.

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The biological action of saponins in animal systems: a review

Biodegradable polymers and their layered silicate nanocomposites: In greening the 21st century materials world

Pectin is an important polysaccharide with applications in foods, Pharmaceuticals, and a number of other industries. Its importance in the food sector lies in its ability to form gel in the presence of Ca2+ ions or a solute at low pH. Although the exact mechanism of gel formation is not clear, significant progress has been made in this direction. Depending on the pectin, coordinate bonding with Ca2+ ions or hydrogen bonding and hydrophobic interactions are involved in gel formation. In low‐methoxyl pectin, gelation results from ionic linkage via calcium bridges between two carboxyl groups belonging to two different chains in close contact with each other. In high‐methoxyl pectin, the cross‐linking of pectin molecules involves a combination of hydrogen bonds and hydrophobic interactions between the molecules. A number of factors—pH, presence of other solutes, molecular size, degree of methoxylation, number and arrangement of side chains, and charge density on the molecule— influence the gelation o...

Chemistry and uses of pectin--a review.

The structural and mechanical properties of gels formed from biopolymers are discussed both in terms of the techniques used to characterise these systems, and in terms of the systems themselves The techniques included are spectroscopic, chiroptical and scattering methods, optical and electron microscopy, thermodynamic and kinetic methods and rheological characterisation The systems considered are presented in order of increasing complexity of secondary, tertiary and quaternary structure, starting with gels which arise from essentially ‘disordered’ biopolymers via formation of ‘quasicrystalline’ junction zones (eg gelatin, carrageenans, agarose, alginates etc), and extending to networks derived from globular and rod-like species (fibrin, globular proteins, caseins, myosin) by a variety of crosslinking mechanisms Throughout the text, efforts are made to pursue the link (both from experiment and from theory) between the structural methods and mechanical measurements As far as we are aware this is the first major Review of this area since that of J D Ferry in 1948 — The interest shown by polymer physicists in more complex biochemical systems, and the multi-disciplinary approaches now being applied in this area, make the format adopted here, in our opinion, the most logical and appropriate

Structural and mechanical properties of biopolymer gels

The role of hydrophobic interaction between the ester methyl groups in the gelation of high methoxyl pectins was investigated by using temperature and different cosolutes to modify hydrophobic interaction in a controlled manner. Both rupture strength and gel threshold were found to be partly proportional to the free energy of hydrophobic interaction between CH3-groups in model systems. The size of junction zones and the standard free energy of gelation were proportional to the square of the degree of methoxylation, i.e. to the probability of ester methyl groups being opposed in contiguous lengths of polymer. The contribution from hydrophobic interaction to the free energy of gelation was about half that from hydrogen bonds.

Hydrophobic Interaction in the Gelation of High Methoxyl Pectins

Body mass index (BMI) is used widely as an index of fatness (the proportion of the body as fat) but its application to the low weight and stature populations in developing countries has not been established. As BMI is an indicator of size (the amounts of fat and fat free masses) as well as fatness, its relation to fatness and interpretation as a measure of energy stores may vary in different groups. Very low BMI reflects low fat and fat free mass, a state for greater concern than low fat mass alone, and possibly more typical of chronic energy deficiency.

Could saponins be a useful treatment for hypercholesterolaemia

1 Saponins are steroid or triterpene glycosides which occur in a number of important food plants, including such staples as soya beans ( Glycine max ) and chickpeas ( Cicer arietinurn ) They are known to be hypocholesterolaemic 2 Some saponins form an insoluble complex with cholesterol which prevents its absorption from the small intestine Others cause an increase in the faecal excretion of bile acids, an indirect route for elimination of cholesterol 3 We have investigated the effects of different saponins on absorption of the bile salt sodium cholate from perfused loops of small intestine, in vivo, in the rat Purified saponins from soapwort ( Suponaria Officinalis ), soya beans and quillaia ( Quillata suponaria ) reduced the rate of absorption of the bile salt; soya-bean and soapwort saponins substantially so but quillaia saponin to a much lesser extent 4 These results were explained by the formation of large mixed micelles by bile acid and saponin molecules in aqueous solution These aggregates can have molecular weights in excess of 10 6 daltons, consequently the bile acid molecules incorporated in them are not available for absorption 5 Control of plasma cholesterol and nutrient absorption through dietary saponins could provide substantial health and nutritional benefits in humans

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A mechanism for the hypocholesterolaemic activity of saponins

Quantitative thin layer chromatography was used to estimate the saponin content of 20 common food plants and also of foods prepared from some of them. The food plants found to be richest in saponins were chickpeas (Cicer arietinum), soya beans (Glycine max), lucerne (alfalfa) sprouts (Medicago sativa) and varieties of Phaseolus vulgaris (navy beans, haricot beans, kidney beans). Saponins were not destroyed by processing or cooking. They were present in falafels (prepared from chickpeas), canned baked beans, canned broad beans and protein isolate from faba beans. However, the saponin content of a fermented soya bean product (tempe) was only half that of whole soya beans. Guar meal (Cyamopsis tetragonolobus) contains saponins but only a trace could be detected in samples of guar gum.

David Oakenfull

Papers

Hydrophobic Interaction in the Gelation of High Methoxyl Pectins

Could saponins be a useful treatment for hypercholesterolaemia

A mechanism for the hypocholesterolaemic activity of saponins

Saponin content of food plants and some prepared foods.

Saponins in food—A review