Phenolic Content, Composition, Antioxidant Activity, and Their Changes during Domestic Cooking of Potatoes

Potatoes in the diet contribute significantly to antioxidant daily intake worldwide. The influence of different domestic cooking conditions, boiling, microwaving, and baking, on total phenolics (TP), antioxidant capacity, phenolic composition, and tryptophan content was studied using eight commercial potato varieties. The antioxidant capacity was detected by the methods of oxygen radical absorbance capacity assay (ORAC) and the 2,2-diphenyl-l-picrylhydrazyl free radical (DPPH center dot) assay. The phenolic composition and tryptophan content were determined using high-performance liquid chromatography coupled with a diode array detector (HPLC-DAD), whereas phenolics and tryptophan were identified by means of HPLC-mass spectrometry, HPLC-DAD, and authentic standards. Antioxidant capacity was influenced by potato variety and cooking conditions; however, cooked potatoes retained 68-97% ORAC value depending on cooking procedure and variety. Chlorogenic acid and its isomers dominated the phenolic composition of each variety involved in this study. ORAC and TP were highly and positively correlated (r = 0.9119). Norkotah ranked highest in chlorogenic acid content and antioxidant value. Principal component analysis showed different cooking processes did not influence the trend of the antioxidant profile of the eight potato varieties, but specific compounds exert influence on the antioxidant capacity. The results imply that the potato varieties rich in antioxidant components could be good antioxidant sources as activities are not greatly affected by different cooking conditions.