EFFECT OF CHEMICAL MODIFICATIONS ON THE PHYSICOCHEMICAL PROPERTIES OF STARCH FROM JACKBEANS (Canavalia ensiformis)

Abstract

Underutilized legume, Jackbeans (Canavalia ensiformis) starch was isolated and subjected to chemical modifications by acetylation and oxidation. The physicochemical properties of the native starch and modified derivatives were determined. K, Na, Ca, P and Mg were the most abundant minerals in all the samples. Results on the antinutrients determined showed tannin, saponin , oxalate and phytate were in the range values of 2.37 - 3.88 mg/g, 3.91 - 6.04 mg/g , 3.56 - 5.02 mg/g and 0.32 - 0.59 mg/g respectively. There were significant differences in functional properties between native and chemically modified starches from jackbeans, so chemical modification improved functional properties; oxidation improved the water and oil absorption capacity of the native jackbeans starch and also the swelling properties was significantly improved. The solubility reduced upon oxidation. Hypochlorite oxidation and acetylation of the starch samples were studied for pasting properties, such as gelatinization temperature, paste viscosity, retrogradation and stability by using Rapid Visco-Analyzer (RVA). The paste clarities of the oxidized starch were better than the acetylated and unmodified starches. The acetylated and unmodified starches allowed 90% transmittance at 650 nm. This may be due to bulky acetyl groups which caused stearic hindrance. Modification influenced the stability of the starch studied. The oxidized starch had better stability than those of the corresponding acetylated and unmodified starch. The infra red spectra of native and chemically modified derivatives indicated similar peaks, except for the additional peak in the acetylated sample at 1649 cm-1 indicating the carbonyl bands stretching vibrations and another peak at 3430 cm-1 on oxidized sample which may be due to the –OH stretching vibration of carboxylic acid groups. These bands confirmed that modifications was successfully carried out. The granule morphologies investigated using scanning electron microscopy showed significant difference in the ratio of crystalline and amorphous regions. However, the modification of native jackbeans starch did not affect the shape, appearance and structural arrangement of the starch granules. The granules were polygonal in shape with size range of 18.20 to 30.68 μm. Thus, chemical modifications altered physicochemical properties of jackbeans starch for better industrial applications, stability and improved retrogradation.