PHYSICOCHEMICAL AND RHEOLOGICAL PROPERTIES OF GUM FROM Guazuma ulmifolia SEEDS

Abstract

Vegetal polysaccharides are extensively used in different industries, particularly in food manufacture. Increasing demand is driving the search for alternative, underexploited polysaccharide sources. West Indian elm Guazuma ulmifolia (Malvacae) is a tree native to Yucatan, Mexico. It is used for shade, its wood is harvested and its fruit used as livestock feed. Its seeds secrete a mucilage that has not yet been characterized and evaluated for use in industrial applications. Physicochemical characterization was done of gum extracted from the mucilage released by G. ulmifolia seeds. The seeds were soaked in water at 60 ºC for 60 min and the gum precipitated from the resulting mucilage with 95% ethanol. The gum contained 15.7% moisture, 81.6% carbohydrates and 7% protein, with a mineral content comparable to commercial vegetal source hydrocolloids. Sugar composition analysis by HPLC identified galactose, glucose, mannose and uronic acids (UA) in a Gal: Glc: Man: UA ratio of 1: 0.4: 2.2: 0.1 (µg/100 mg). The consistency index (k) at 25 ºC was 14.8 Pa∙ s. Viscosity decreased as shear rate increased, showing the gum to be a refluidizing (pseudoplastic) type. Uronic acids content (13.8 µg/ 100 mg) and negative zeta potential values indicate the gum to have an anionic charge with high solubility at alkaline pH and low solubility at acid pH. The G. ulmifolia seed gum has potential uses in food systems and technological processes such as encapsulation.