The effect of thermal processing and storage on the physicochemical properties and in vitro digestibility of potatoes

Shepody potatoes were cooked using three common cooking methods - microwaving, boiling and pressure cooking. Microwaving for 2.5 min retained the highest amounts of slowly digestible starch (SDS, 19.6%) and resistant starch (RS, 48.8%) as compared to the other cooking treatments. Similarly, enthalpy and FTIR results (ratio of 1047/1022 cm(-1)) were also higher for microwaved samples, again indicating incomplete gelatinisation. Potatoes were also boiled for 15, 30 or 45 min, followed by 1, 3 or 7 days retrogradation at 23 or 4 degrees C. Retrogradation enthalpy increased significantly (P = 0.05) with increased storage time and decreased storage temperature; FTIR results displayed temperature dependency; at 4 degrees C, ordered structure increased with increasing storage time, whereas the opposite trend was seen at 23 degrees C. Lastly, formation of SDS and RS was favoured for longer boiling times (30 - 45 min), extended storage times (3-7 days) and 4 degrees C.