Isolation and characterization of tamarind seed (Tamarindus indica L.) polysaccharide.

The alcohol-insoluble fraction from the water extract of tamarind seed meal, constituting 60 to 65 per cent of the husked kernel, has been described as a rich source of pectin (l-3). Although it forms a firm jelly in the presence of appropriate amounts of sugar and acid (1,4) and has been suggested for commercial use as a substitute for pectin (5), it has been shown in preliminary communications by the authors (4, 6-8) and later by others (2,3, 9-11) that it differs fundamentally from fruit pectins. Pectins are characterized by the presence of methyl ester groups and galacturonic acid units (12) with varying amounts of arabinose and galactose, presumably derived from associated araban and galactan, loosely attached to the molecule (13-15). On decomposition pectins also yield pectic acid, a product of definite chemical composition (16, 17), which is obtained either directly (18) or, better, through the insoluble calcium salt (19, 20) after hydrolysis by mild alkali followed by neutralization with acid. This paper records the results of investigations on the nature of the polysaccharide fraction of tamarind seed which show how in all these respects it differs from pectins, a conclusion necessitating revision of the views held hitherto to account for many of the phenomena of pectin-sugar-acid jelly formation (21, 22).