The chemical constitution of the gums

Abstract

THE latest work which has been carried out on gums is not of very recent date, and advances in carbohydrate chemistry which have been made since that time make it desirable that this work should be repeated.The physical difficulties of working with these substances are considerable, and the situa- tion is aggravated by the fact that the natural gums are frequently composed of mixtures of several individual types.Separation of such mixtures is very difficult, and it is probable that physical methods based on their colloidal properties will have to be elaborated.Early investigators have shown that the hydrogen and oxygen in gums exist in approximately the same proportions as in water, and accordingly the gums were considered to be true carbohydrates.Later, by the action of acids, various sugars were obtained from them by hydrolysis, and the gums were thereupon classified as polysaccharides.Still later, it was demonstrated that they are not of a true polysaccharide nature, since they consist of numbers of sugar molecules united to a central nucleus of a sugar acid nature.The attachment seems to be of an ethereal or glucosidic type, and not an ester type, since the gums retain acidic properties, and are capable of forming salts.In point of fact, they are usually found as salts of calcium, magnesium, or potassium.It is to be emphasised that the classification of a substance as a gum is as yet mainly an arbitrary one, not being based on any constitutional know- ledge, but decided by its origin and physical behaviour, together with the fact that it is of a carbohydrate nature.When the chemical composition of these substances has been determined, it may be possible to suggest a more rational grouping, and also to speculate with some degree of probability as to their role in nature.The first member of this group to be studied was gum arabic, since from the work of previous investigators this appears to be a single substance.