Simultaneous determination of major anthocyanins in purple sweet potato

A simultaneous determination method using HPLC was carried out to determine the net content of anthocyanins (AN) in purple sweet potatoes (PS) and processed foods made from them. The optimum HPLC conditions, which allowed good separation of the peaks of eight major ANs (named YGM-1a, -1b, -2, -3, -4b, -5a, -5b and -6) in the storage root of PS cultivar Ayamurasaki, were set by employing formic acid as an acidified solvent. Under these conditions, analysis was conducted in 40 min, which is considerably shorter than the time taken in previous experiments. In HPLC analysis of standard pigment YGM-6, the calibration curve showed a good linear correlation between concentration and peak area in the concentration range 10^-6-10^-3 M, and the detection limit for analysis was less than 11 ng. Moreover, the introduction of a quantitative factor by comparison of a standard YGM-6 peak area with the experimental YGM peak areas simplified the simultaneous determination. This method was applied to fresh PS, dried PS powder and processed PS-based beverages (a carbonated drink and a fermented vinegar). The total major AN content was 369.1 mg/100 g in raw PS (cv. Ayamurasaki), with YGM-4b present in the largest amount, and peonidin-based ANs making up 81% of total AN levels. The compositions of major ANs in the dried powder, carbonated drink and fermented vinegar were similar to that of raw PS, with the total contents at 196.9 mg/100 g, 118.7 mg/100 g and 15.3 mg/100 g, respectively.