Chemical and physical characterization of guar galactomannan extracted from guar seeds

Abstract

Guar is becoming a highly valuable crop for West Texas due to its drought tolerance and potential use in hydraulic fracturing in shale gas and oil harvesting. Guar gum is chemically known as galactomannan, a heteropolysaccharide of galactose and mannose. Galactomannan is concentrated in the endosperm of the guar seed and is a storage polysaccharide which reserves energy for seed germination. It is mainly used in hydraulic fracturing, paper, textile, pharmaceutical and food industries. Full characterization of guar gum (Galactomannan) using different analytical tools is very important to understand the chemistry of the gum to optimize the industrial applications. However, limited number of studies has been conducted to characterize the gum extracted from currently available guar germplasm. Therefore, galactomannan extracted from two leading guar cultivars in West Texas was characterized using different analytical tools to elucidate physical and chemical differences. Pure guar galactomannan and food grade guar gum were also used as reference materials for the characterization. Extraction of the gum from guar seeds is critical because impurities in the gum have great impact on the behavior of guar solutions. Therefore, gum was extracted with minimal contamination with continuous sample assessment using Fourier Transform Infrared Spectroscopy (FTIR) to determine the level of contamination. Then, the gum was characterized by High Performance Liquid Chromatography (HPLC), Thermogravimetric Analysis (TGA), X-Ray Diffractometer (XRD) and FTIR to determine mannose and galactose contents, thermal stability, level of crystallinity and chemical composition of the gum respectively. Scanning Electron Microscope (SEM) was employed to visualize the morphology of guar seeds.