Physicochemical and bread-making properties of flours from sweet potatoes with different flesh colours

Abstract

Flour was prepared from Korean sweet potatoes (SPs) with different flesh colours (white, yellow/orange, and purple) and evaluated for physicochemical and pasting properties and their partial substitution for bread-making. SP tubers were soaked in sodium metabisulfite solution (anti-browning agent) and subjected to hot air drying, followed by grinding. SP flours with different colours showed variations in chemical compositions, especially amylose, dietary fibre, and starch contents. Yellow/orange-fleshed SP flour had the highest content of total carotenoid (5.26 mg/100 g) among all SP flours. The highest total anthocyanin content (59.92 mg/100 g) was reported for purple-fleshed SP flour. Water absorption index (WAI), water solubility index (WSI), and an oil absorption of purple-fleshed SP flour were 1.63 g/g, 25.59%, and 187.21%, respectively, and relatively higher than those of white or yellow/orange-fleshed SP flour. Wheat flour was substituted with SP flour in bread at 10-30% level. The increase in the proportion of SP flour resulted in a significant decrease in loaf volume, and maximum reduction in loaf volume was reported for the bread containing purple-fleshed SP flour. However, SP flour may serve as a substitute for wheat flour at levels up to 10% without causing any deteriorating effects on the overall bread quality. Therefore, coloured SP flour could be useful in the bread-making industry to improve the nutritional value of bread.