Biochemical Changes in Cream and Orange-fleshed Cured Sweet Potatoes Cooked under Different Modes

The importance of sweet potato (  Ipomoea batatas L.) as a health food, contributed by carotenoids, anti-oxidants, phenolics, dietary fiber and anthocyanins is increasingly recognized in several countries. Browning, resulting from enzymatic and non-enzymatic reactions is a major problem for processed sweet potato. With a view to developing functional foods from sweet potatoes, the biochemical changes during curing of cream and orange-fleshed sweet potatoes and during cooking under different modes like boiling, microwave baking and hydro-thermal cooking were studied at Central Tuber Crops Research Institute, Thiruvananthapuram, India. Decrease in starch and increase in sugars during curing were more in the orange-fleshed variety, while total free amino acids and phenols did not change during curing. Citric acid/ascorbic acid and sodium sulfite promoted more leaching of starch during boiling, especially from cream-fleshed variety. Microwave baking (900 W; 5 min) of fresh and cured sweet potatoes, resulted in a sharp decrease in starch and increase in sugars. Retention of amino acids was maximum in hydro-thermally cooked roots. Total phenolics increased in whole roots with peel during boiling/hydro-thermal cooking, while microwave baking resulted in lower phenol levels. Microwave baking of cured sliced sweet potato roots was the best technique to reduce starch and increase soluble solids, with very low levels of total phenols.