| In order to overcome the severe interferences of color and high content γ-oryzanol in the detection of acid value of rice bran oil by traditional manual indicator titration method, according to the classical theory of acid base titration, using methods of automatic potentiometric titration and “second graph”, a detection method of the acid value of rice bran oil was established. Using this method, the pH-titration volume curve and corresponding first-order difference curve of acid base titration were drawn by computer real-timely and synchronously, then the “pH jump” in these curves, which was caused by the neutralization of free fatty acids, was taken as the foundation for judgment of titration end point. The results showed that the titration end points of free fatty acids and γ oryzanol could be distinguished correctly by automatic potentiometric titration method, therefore the interference of γ oryzanol in the detection of acid value of rice bran oil could be excluded. By contrastive experiments, it was found that the acid values of many kinds of vegetable oils detected by automatic potentiometric titration method were very close to those detected by traditional manual indicator titration method; while the acid value of rice bran oil detected by traditional manual indicator titration method was 0.3-1.0 mgKOH/g higher than that detected by automatic potentiometric titration method. Therefore, the acid value of rice bran oil could be detected accurately by automatic potentiometric titration method. |
