Antioxidant Activities of Different Sweet Potato Cultivars and Their Thermal Stability
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Abstract:
To compare the phenolic contents and antioxidant activities of extracts from different sweet potato cultivars, cold acetone, and sodium hydroxide-ethyl acetate were used to extract the free and bound phenolics from sweet potato skin and flesh, respectively. Folin-Ciocalteu assay and the sodium nitrite-aluminum nitrate-sodium hydroxide colorimetric method were applied to measure the phenolic and flavonoid content, and the antioxidant activities were evaluated by the oxygen radical absorbance capacity (ORAC) method. It was found that total phenolic and total flavonoid content of peels were higher than those of corresponding flesh. Among different cultivars, the purple skin-purple flesh (PP) sweet potato had the highest phenolic content of （336.87±2.83）?10-2 and （121.79±1.68）?10-2 mg GAE/g in skin and flesh, respectively. The ORAC value of PP skin extract was the highest at （6917.79±672.70）?10-2 μmol TE/g, while the ORAC values of flesh extracts from different cultivars showed no significant difference. The effects of heat treatment on the phenolic and total flavonoid content and the ORAC value of PP flesh were also investigated. The phenolic content, flavonoid content, and ORAC values of samples heated at 100 ℃ for 30 min were 2-fold, 2.6-fold, and 5.7-fold higher than those of the unprocessed sweet potato, respectively, indicating that heat treatment could favor the release of phenolic compounds in sweet potatoes and enhance their antioxidant activities.
