Inactivation of nisin by glutathione in fresh meat

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) was used to determine the fate of nisin in meat products. Nisin in 0.02N HCl was added to fresh and cooked meat and meat juice and samples were stored at 4 degrees C overnight. Residual nisin solutions and meat juice and meat extract supernatants were analyzed for antimicrobial activity and for nisin. Nisin was recovered from cooked meat extract and cooked meat juice; however, only nisin bound to a food component was detected in fresh meat extract. Mass spectra for raw meat and juice showed a signal 307 Da greater than the mass of nisin. Results indicated that nisin was likely inactivated in raw meat by an enzymatic reaction with glutathione.