| A new cupric acetate-pyridine colorimetric method used for specific determination of FFA in oils, fats and foodstuffs was established. The optimal detection wavelength of the new method was optimized, the effects of solvents on the color intensity and the solubility stability of oils and fats were studied, and the effects of different kinds of FFA on the color intensity were also studied. In addition, the influences of edible oil sample washing, acidic food additives and acidic food flavors on the determination of the new method were also studied. The results showed that the best detection wavelength was 710 nm, and cyclohexane was the ideal solvent. Cupric acetate-pyridine colorimetric method could effectively eliminate the interference of acidic food additives and other non-FFA acids. The determination of acid value in liquid oil (0.1-5.0 mg/g) and solid fat (0.2-10.0 mg/g) was achieved by using oleic acid as colorimetric calibration. For edible oils without acid interference, the detection results correlated well with the traditional acid-base titration method (R2＞0.996). Overall, the recovery was 913%-93.8% and the relative standard deviation of reproducibility test was less than 3%. Each test only required 1 g of oil and fat sample. In conclusion, the cupric acetate-pyridine colorimetric method served as an efficient, accurate, and convenient alternative for the determination of acid values of oils, fats, and foodstuffs as well. |
