Physicochemical, thermal properties and microstructure of six varieties of taro (Colocasia esculenta L. Schott) flours and starches

Taro (Colocasia esculenta L. Schott) flours were prepared from six varieties of taro corms coded as RIN, RIE, CN, CE, KW1 and KW2. Starch yields prepared from the flours varied between 66.5% for KW2 to 86.61% for RIE. The proteins content varied from 2.9% for KW1 to 4.9% for CN in the flours. Taro starch had irregular, polygonal shapes and small granular sizes. A wide variation was observed in the granular diameter of each of the starch samples and between the samples. The amylose contents varied from 14.7 +/- 1.64% to 30.85 +/- 0.63% as determined by the DSC method. The taro starch contained 0.2-0.6% lipids and 2% ash. The onset gelatinisation temperatures of the taro flours varied from 55.2 to 65.49 degrees C, whereas those of the starches are between 48.08 +/- 2.46 for KW2 and 64.37 +/- 2.35 degrees C for KW1. Retrogradation of the starches and the flours, as measured by their enthalpy changes, appeared to vary significantly between the varieties. The water absorption capacity varied from 240% to 470% and from 60% to 250% for the flours and starches samples, respectively. Taro flours had higher solubility index than their starch counterparts. Among the varieties, RIN and CE starches had the highest solubility whereas KW1 starch had the lowest. The sorption study also revealed the high ability of the taro flours to absorb water compared to their starch components. (C) 2007 Elsevier Ltd. All rights reserved.