Nisin Migration in Shelf Stable, Tuna-Filled Tortillas During Storage

Abstract : This report summarizes a 1-year study, completed in November 2012, of the effectiveness of nisin as a bacteriocin in tuna-filled tortillas during storage, as part of the Next Generation Hurdle Technologies (NGHT) Program. This Department of Defense, Combat Feeding Directorate Program provides not only the foundation for the development of innovative intermediate moisture (IM), eat-on-the-move ration components, but also an opportunity to improve existing IM ration components, which rely on controlling both the product's water activity (aw) and pH. The NGHT Program lowers these boundaries, i.e., increases pH and aw, of existing hurdles, using food-grade bioactive compounds to yield a higher quality ration component without compromising food safety. Ham, chicken, and tuna spread wraps were formulated with nisin because it is generally regarded as safe and as the most effective bacteriocin with possible use at lower concentrations when used in conjunction with other bacteriocins. However, nisin is only added to the tuna filling, not to the wrap. Thus there is concern that the nisin may migrate from the filling to a tortilla wrap during storage, thereby diluting bacteriocin concentration in the tuna, reducing the total bacteriocin activity and increasing the possibility of microbial/pathogen growth. The purpose of this study was to determine if nisin migrates from the tuna filling to the wrap during storage at 25 degrees C.