Effects of various traditional processing methods on the all-trans-β-carotene content of orange-fleshed sweet potato

The effects of traditional preparation methods and drying procedures on the provitamin A carotenoid content of orange-fleshed sweet potato (OFSP) roots was determined by a high-performance liquid chromatography (HPLC) method. All-trans-β-carotene was the major provitamin A carotenoid and the mean content of seven improved OFSP cultivars ranged from 108 to 315 μg/g dry matter. The retention of all-trans-β-carotene was 78% when OFSP were boiled in water for 20 min. When OFSP were steamed for 30 min the retention was 77%, whereas deep-frying OFSP roots for 10 min resulted in retention levels of 78%. Drying slices of OFSP roots at 57 °C in a forced-air oven for 10 h reduced the all-trans-β-carotene content by 12%. Solar drying and open-air sun drying OFSP slices to a moisture content of ⩽10% resulted in all-trans-β-carotene losses of 9% and 16%, respectively. The cis-isomer 13-cis-β-carotene was found in noticeable amounts in all processed samples, but not in any raw samples. The formation of 13-cis-β-carotene correlated with the original amount of all-trans-β-carotene found in the raw OFSP root. The high content of all-trans-β-carotene in the investigated improved OFSP varieties and the moderately low losses due to degradation and isomerization renders OFSP a suitable food source of provitamin A.