The potentiality of a native isolate, Pediococcus acidilactici C20, to produce quantifiable amounts of pediocin C20 on whey permeate was studied. The molecular basis for the presence of a P-gal like gene was shown by DNA dot-blot technique followed by beta-galactosidase (beta-Gal) assay on native polyacrylamide gel as experimental evidence for lactose hydrolysis. Production of pediocin C20 was found to be 1-1.5-fold excess in lactose-based medium as compared to medium with glucose. Optimized whey permeate supplemented with 2% yeast extract gave cell growth of 3.5, OD600 and pediocin C20 activity of 150 x 10(3) AU ml(-1) equivalent to that obtained by growth in commercial MRS broth. (c) 2004 Elsevier Ltd. All rights reserved.