Cooking sweetpotato roots increases the in vitro bioaccessibility of phytochemicals and antioxidant activities, but not vitamin C

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The percent bioaccessibility of phytochemicals and antioxidant activities (ABTS and FRAP) of cooked sweetpotato storage roots (peeled and unpeeled) of varying flesh colours was assessed in vitro. Generally, the phytochemicals’ bioaccessibility increased with cooking compared to the raw roots, except in vitamin C. The raw roots had vitamin C bioaccessibility of 92 %, while for cooked, it ranged between 61 % (baking) and 73 % (frying). For phenolics and flavonoids, peeling the roots significantly (P < 0.001) increased bioaccessibility by 11 % and 4 %, respectively. For the other phytochemicals, the bioaccessibility of peeled roots did not differ significantly (P > 0.05) from unpeeled ones. Cooked roots had higher antioxidant activities than in raw. Vitamin C may have acted as a pro-oxidant as it was the only phytochemical with inverse relation with antioxidant activities. Boiling, steaming, baking, frying, or microwaving sweetpotato roots increases the in vitro bioaccessibility of phytochemicals and antioxidant activities, but not vitamin C.