Composition and color stability of anthocyanin-based extract from purple sweet potato

Purple sweet potato (PSP) can provide products with attractive color besides nutritious benefits in food processing. So, the compositions and color stability of an aqueous anthocyanin-based PSP extract were investigated in order to promote its wide use in food industry. PSP anthocyanins were extracted with water, and nine individual anthocyanins (48.72 ug mL(-1) in total, 24.36 mg/100 g fresh PSP in yield) were found by HPLC analysis. The PSP extract also contained 17.11 mg mL(-1) of protein, 0.44 mg mL(-1) of dietary fiber, 2.82 mg mL(-1) of reducing sugars, 4.02 ug mL(-1) of Se, 54.21 ug mL(-1) of Ca and 60.83 ug mL(-1) of Mg. Changes in color and stability of the PSP extract, as affected by pH, heat, light and extraction process, were further evaluated. Results indicated that PSP anthocyanins had good stability at pH 2.0-6.0, while the color of PSP extract kept stable during 30 days of storage at 20 degrees C in dark. Both UV and fluorescent exposure weakened the color stability of PSP extract and UV showed a more drastic effect in comparison. A steaming pretreatment of fresh PSP is beneficial to the color stability.