Three underutilised sources of starch from the Andean region in Ecuador Part I. Physico-chemical characterisation

The physico-chemical aspects of three native Andean starches from Arracacha xanthorriza, Canna edulis and Oxalis tuberosa were investigated. Scanning electron microscopy-investigations showed that granules of A. xanthorriza were the smallest with irregular shape and sizes between 7 and 23 μm, whereas granules of O. tuberosa and C. edulis were both ovally shaped with granular sizes between 20 and 55 μm and 35–101 μm, respectively. All three starches revealed a B-type X-ray diffraction pattern. The gelatinisation behaviour was investigated using differential scanning calorimetry (DSC). The gelatinisation enthalpy was 14.6 J/g of starch for O. tuberosa, 15.7 J/g for C. edulis and 17.6 J/g for A. xanthorriza, and the peak temperature of the endothermic DSC-transition was 55.9, 61.2 and 60.1°C, respectively. The amylose content determined by gel permeation chromatography after debranching with isoamylase was 4% for A. xanthorriza, 18.4% for O. tuberosa, and 23.8% for C. edulis. The amylopectin showed different structures among the three starches with a β-amylolysis limit of 67.6% for C. edulis, 64.5% for O. tuberosa and 56.6% for A. xanthorriza. The average chain length of the amylopectin was highest for A. xanthorriza (22.6), followed by O. tuberosa with 22.4, and lowest for C. edulis (21.9). The complexation ability of the three starches was investigated by adding sodium dodecyl sulphate (SDS), and the amylose content was positively correlated with the enthalpy of the amylose–SDS complex.