Effect of Modifications on the Chemical Composition, X-Ray Diffraction Pattern and Scanning Morphology of Starches from Cocoyam (Colocasia esculenta and Xanthosoma sagittifolium)

Abstract

The effect of annealing, heat moisture treatment and citric acid on major physicochemical properties of cocoyam starch was investigated. This was done in order to establish the optimum processing condition with the aim of enhancing the utilization capacity of the starch. Starch extracted from red and white Cocoyam (Tania) Xanthosoma sagittifolium and Taro Colocasia esculenta cultivars respectively were subjected to modification using annealing, heat moisture treatment and citric acid methods. The modified and native starch samples were analyzed for chemical composition using standard methods, likewise the x-ray diffraction pattern and starch granules morphology of the samples were assessed. The result showed that amylose content ranged from 24.81 - 38.16%, protein 0.00 – 0.77%, ash 1.19 – 3.16 and carbohydrate 84.19 – 86.79%. The X-ray diffraction patterns of red and white cocoyam starches showed a strong peak at 15o, 18o and 23o (2ø) indicating A-type starch. Colocasia esculenta starch also displayed A-type diffraction pattern with additional peak at 24o. The modification methods used did not change the diffraction pattern of the starch samples but only influenced the intensity of the diffraction peak. The scanning electron micrographs showed that the starch granules were small to medium in size with most having irregular shape and smooth surface. Annealing and citric acid caused little noticeable fractures on some granules without compromising starch granules integrity. Heat moisture treatment however resulted in evident loss of starch granules integrity. The modification methods affected the physicochemical properties of cocoyam starch samples in a varying pattern which may qualify the starch samples for use in different food and non-food applications.