Physico-chemical and pasting properties of starch from stored potato tubers

Starch was separated from tubers of four potato (Solanum tuberosum L.) cultivars, viz. 'Kufri Jyoti', 'Kufri Sindhuri', 'Kufri Chipsona-1' and 'Kufri Chipsona-2' before and after 90 days of storage at 4, 8, 12 and 16 degrees C and, morphological, physico-chemical and pasting properties were studied. Scanning electron microscopy showed oval and irregular shaped starch granules with average diameter of 15 mu m, and the granule diameter increased after storage. Peak viscosity was lower after storage at 8 degrees C and higher at 16 degrees C. Hot paste viscosity decreased while breakdown viscosity and set back viscosity increased after storage, and there was no significant change in cold paste viscosity. A significant decrease in pasting time and increase in pasting temperature was observed after storage. Phosphorus content showed significant positive correlation with peak viscosity (r = 0.452, p < 0.05) and breakdown viscosity (r = 0.685, p < 0.01), and a negative correlation with amylose content (r = -0.674, p < 0.01). 'Kufri Sindhuri' starch showed significantly (p < 0.05) higher peak, hot paste, breakdown and cold paste viscosity. The X-ray diffraction pattern of starch showed a distinctive maximum peak at around 17 degrees, 2 theta and it was not affected by the cultivar or storage temperature.