Structural and physicochemical characterization of funoran extracted from Gloiopeltis furcata by different methods

Abstract

Funoran is a sulfated polysaccharide extracted from the red algal Gloiopeltis species with wide uses in many applications such as thickener and adhesive. This study applied two extraction strategies to obtain funoran from Gloiopeltis furcata with various physicochemical properties. In strategy 1, direct hot water extraction (95 °C for 3 h) yielded two funoran fractions. In strategy 2, algae were purified by cold water before hot water extraction (95 °C for 3 h), resulting in two more fractions. FTIR and NMR measurements showed that all fractions were composed of repeating β-d-galactose-6-sulfate and 3, 6-anhydro-α-l-galactose units as the backbone with small amounts of substituents. The highest molecular weight fractions extracted from both methods were polydisperse with approximately 51 % polysaccharides, 5.2 % protein and less than 1.4 % uronic acid with similar structural compositions of funoran. All funoran fractions in a 1.5 % aqueous solution (w/w) exhibited shear thinning behavior at 20 °C. The fractional difference in strategy 2 was clearly observed in which the high molecular weight formed a highly viscous and cloudy solution with low solubility, while the low molecular weight was highly soluble and formed a clear and transparent solution. Upon cooling, funoran fraction solutions exhibited a steep increase in complex modulus │G*│ indicating the gel formation. On reheating, these gels melted at higher temperatures with significant thermal hysteresis and micro-DSC measurements showed peaks confirming the gelation.