Development of HPLC and NACE methods for the simultaneous determination of benzoic and sorbic acids in sour snap beans containing oil

The practical methods were developed for the simultaneous determination of benzoic acid (BA) and sorbic acid (SA) in sour snap bean samples containing oil. BA and SA in the samples were extracted by ultrasonication with water, followed by cleanup procedures with precipitation for removing the potential proteins and with petroleum ether liquid-liquid extraction for removing the edible oil contained in the samples. The HPLC method was developed using Supelco C18 (250 min x 4.6 mm. id, 5 mu m) as column, MeOH-20 mM NH4Ac (25:75 v/v) at 1.0 mL/min as the mobile phase and 230 rim. as the detection wavelength. The optimal NACE method was established with a running buffer of 20.0 mM NH4Ac in 95% MeOH (pH* 10.6), and an applied voltage of -30 kV over a capillary of 50 mu m id x 48.5 cm (40 cm to the detector window), which gave a baseline separation of BA and SA, and as well as of the blank matrix within ca. 10 min. Both HPLC and NACE methods gave the relatively lower limits of quantification at about 0.01-0.02 and 0.04-0.05 mg/kg, respectively, whereas the overall recoveries were larger than 85.0%. The proposed methods have been successfully applied to measure 15 real sour bean samples and the content profile of BA and SA in sour bean samples was obtained and evaluated.