Electrochemical determination of free amino nitrogen in aged lean beef by the measurement of surplus acid after neutralization.

In this study, an electroanalytical method, which is based on the concept of acid-base back titration and the electrochemical sensing of acids by means of the reduction of quinone, is proposed for determining free amino nitrogen (FAN) in lean beef samples. To perform the electrochemical determination of FAN in beef samples, the following voltammetric behaviors of 3,5-di-tert-butyl-1,2-benzoquinone (DBBQ) in the presence of acid have been applied: (1) A cathodic prepeak height of DBBQ caused by HCl (iH) is proportional to the HCl concentration in the electrolyte solution. (2) iH is linearly decreased with an increase in amino acids concentration in the electrolyte solution after the amino acids are neutralized by excess HCl. By the present electroanalytical method, FAN in a lean beef sample was determined to be 4.70 mgN g-1 with a repeatability of 3.4% relative standard deviation (n = 5). This result by the present electroanalytical method was in good agreement with a colorimetric method using a ninhydrin reagent. Moreover, the present electroanalytical method was able to monitor increases of FAN in lean beef samples during wet-aging. These results demonstrate the present electroanalytical method could help in the development of an on-site analysis for estimating aged beef samples via the determination of FANs.