Effects of Curing, Storage Conditions, and Cooking on the Composition of Sweet Potatoes

Abstract

'Beniaka' and 'Beniazuma' are major sweet potato cultivars (Ipomoea batatas L.) in the fresh vegetable market. Their roots have good quality profiles as to shape, surface color, and flavor. Freshly harvested roots of 'Beniaka' and 'Beniazuma' contain 23 approximately 26 and 27 approximately 30% starch, 0.5 and 1.0% organic acids, respectively, and 2% sugar. Sucrose content of both cultivars increased by 2.5% during curing (held for 7 days at 30-degrees-C and 98% RH) or during storage for 1 month at 13-degrees-C. After storage for 4 months at 13-degrees-C, sucrose content of uncured 'Beniaka' roots increased, whereas it changed slightly in uncured 'Beniazuma' and cured 'Beniaka' roots. Sucrose content of 'Beniaka' roots also changed little when stored at 15-degrees-C and/or 98% RH. Changes in sugar contents and enzyme activities indicate the possibility that sucrose synthase was more active in sucrose metabolism than was sucrose phosphate synthase. Starch in 'Beniaka' and 'Beniazuma' roots cooked immediately after harvest was converted to 7 and 14% maltose, respectively. The amount of starch converted to maltose by cooking increased in 'Beniazuma' roots which were previously stored at 13-degrees-C. Texture of 'Beniazuma' roots was mealy when cooked immediately after harvest but the roots gradually became more moist with storage at 13- degrees-C. Textural properties of cooked 'Beniazuma' roots did not correlate well with sugar and starch contents of the fresh or cooked sweet potatoes.