Malva nut gum. (Part I): Extraction and physicochemical characterization

Abstract

Malva nut is the seed of Scaphium scaphigerum and has long been used as a traditional medicine in South East Asia. This paper reports on the extraction and characterization of gums from malva nut seed. Sequential extraction with water, 0.05 M HCl, and 0.05 M NaOH solutions resulted in 1, 6 and 20% gum yield, respectively, based on the dry weight of the seeds. The alkaline extracted gum fraction was further characterized and revealed 62.0% carbohydrates, 8.3% ash and 8.4% protein. The major constituent monosaccharides of the gum were 31.9% arabinose, 29.2% galactose and 29.5% rhamnose, as measured by acid hydrolysis and ion exchange chromatography. The gum also contained 6.4% uronic acid and small amounts of glucose, xylose and mannose. Methylation analysis revealed that alkaline extracted malva nut gum was primarily composed of terminal l-Ara f, 1,3-linked l-Ara f, 1,4-linked d-Gal p, 1,4-linked d-GalA p with small amounts of branching units: 1,2,4-linked d-Gal p and 1,2,3,4-linked Rham p. The gum showed a single peak in the size exclusion chromatography from which the average molecular weight and intrinsic viscosity were determined to be 6.65×10 6 Da and 10.0 dl/g, respectively. These values are much higher than the many commercial hydrocolloid gums. Further purification of the gums by dialysis, against deionised water, and decoloring by hydrogen peroxide treatment reduced the molecular weight and intrinsic viscosity of the polysaccharides.