Sugars and polyols stablize proteins against heat denaturation. Scanning calorimetry was used to obtain a quantitative estimate of the degree of stabilization. Solutions of ovalbumin, lysozyme, conalbumin, and alpha-chymotrypsinogen were heated at a constant rate, and the temperature of the maximum rate of denaturation was estimated (Tm). Addition of a sugar or polyol raised Tm. The magnitude of the stabilizing effect (delta Tm) depended on both the nature of the protein and the nature of the sugar or polyol, ranging from 18.5 degrees C for lysozyme at pH 3 in the presence of 50% (w/w) sorbitol to 0 degrees C for conalbumin at pH 7 in 50% glycerol solution. It is argued that this stablization is due to the effects of sugars and polyols on hydrophobic interactions. The strength of the hydrophobic interaction was measured in model systems in sucrose and glycerol solutions. Sucrose and glycerol strengthened the pairwise hydrophobic interaction between hydrophobic groups; however, they reduced the tendency for complete transfer of hydrophobic groups from an aqueous to a nonpolar environment. The extent of stabliziation by different sugars and polyols is explained by their different influences on the structure of water. The difference between the partial molar volume of the sugar or polyol and its van der Waals volume was used as a rough quantitative measure of the structure-making or structure-breaking effect. There was a linear relationship between this quantity and delta Tm.

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 CHs-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.

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 106 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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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 weie chickpeas (Cicer arietinum), soya beans (Cl-vcine max), lucerne (alfalfa) sprouts (Medicago sutivu) and varieties of Phuseolus 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 tetragonolobiw) contains saponins but only a trace could be detected in samples of guar gum.