Jenseniin G is an antibotulinal bacteriocin (antimicrobial peptide) produced by the dairy culture, Propionibacterium thoenii (jensenii) P126. Activity from crude jensemin G preparations isolated from static cultures was not detected in unconcentrated cultures before day 7. Activity was not detectable until the spent culture medium was concentrated 50-100 fold. Maximum activity (21 AU/ml) was observed in concentrated supernates at day 9.