Mustard juices prepared from mustard vegetables were inoculated with the culture ofLactobacillus plantarum CCRC 12942 and various biochemical changes in mustard juice weredetermined during lactic acid fermentation. The pH dropped down, higher titratable acidity andsignificant changes of sugar content were found in all the inoculated trials. The content ofascorbic acid in the control trials changed significantly. However, the least changes of thecontents of ascorbic acid and total phenolics were found, and activities of PPO and POD werenot detected in the blanched trials. The study of mustard brine fermentation by lactic acidbacteria indicated that the color changes of the juice was directly related to enzymatic browningand the degradation of ascorbic acid might also contribute partially to the browning reaction.