Effect of starch pasting temperature on remaining total ascorbic acidcontent in steamedsweet potatoes

Abstract

The ascorbic acidcontent of raw andsteamedstorage roots of 3 sweet potato cultivars with different starch pasting temperatures was measured. The cultivars were nBeniazumap, nHoshikirarip andnQuick Sweetp, andtheir pasting temperatures measuredby RVA were approximately 75?, 65? and55?, respectively. The total ascorbic acidcontents per fresh weight of raw roots of nBeniazumap, nHoshikirarip andnQuick Sweetp were 275.88±38.93 μg/g, 244.70±50.48 μg/g and218. 26±50.20 μg/g, respectively. After steaming, these values changedto 154.27± 31.94 μg/g, 170.20±26.20 μg/g and175. 18±44.38 μg/g. Therefore, about 57 %, 71% and80 % of the ascorbic acid contents in raw roots of nBeniazumap, nHoshikirarip andnQuick Sweetp were remainedafter steaming, respectively. The steaming process resultedin maltose generation at ca.50°C for nQuick Sweetp, ca.60°C for nHoshikirarip andca. 80? for nBeniazumap, according to their starch pasting temperatures. The sweet potato cultivar nOkikoganep in which maltose is not generatedupon heating due to the lack of beta-Amylase activity remainedless than 50% of total ascorbic acidpresentedin raw roots after steaming. These results indicatedthat sweet potato cultivars with low starch pasting temperatures retaineda larger percentage of total ascorbic acidcontent presentedin their raw roots after steaming due to their early generation of maltose.