Multimethod assessment of commercial nisin preparations.

Nisin is a GRAS preservative effective against several Gram-positive organisms including Listeria monocytogenes. Commercial preparations are usually fermentation products containing 2.5% pure nisin along with insoluble material which, in this study, was found to influence the quantification and activity of nisin under different conditions. Commercially available samples of nisin were tested for efficacy using various methods, such as well diffusion, time to turbidity, and GUS (where a reporter compound is induced in response to nisin). SDS-PAGE detected a single peptide band, corresponding with the molecular weight of nisin. Protein quantified using the Bradford method indicated that the carrier of some samples was proteinaceous. Though the activity of commercially available nisin preparations is indicated on the label, end users should determine the effect of changing their source of nisin.