Abstract: A new analytical method to rapidly determine protein content in Vigna minima seeds was established in the present study. Samples were digested with a sulfuric acid-hydrogen peroxide solution by microwave programmed digestion to convert crude protein to NH4+. The NH4+ generated in the solution were further converted to H+ ions for conductivity micro-titration with standard NaOH solution. The results showed that the average content of protein in wild Vigna minima seeds from Zhengzhou was determined to be 23.41% with relative standard deviation (RSD) of 1.5% (n = 5). Compared with the classic standard determination method, the conductivity micro-titration did not exhibit significant difference as analyzed by F-test and t-test at 95% confidence level. This method has the advantages of convenient operation, high sensitivity, quick determination, accurate results and no requirements for indicators.

Key words: microwave program digestion, conductivity, micro-titration method, crude protein, Vigna minima