Implementation of Biofilm Reactor For Nisin Fermentation Using Reduced Nitrogen Content Media With or Without pH Control

Abstract

Nisin, an antimicrobial produced by the fermentation of Lactococcus lactis subsp. lactis, demonstrates an inhibitory effect against selected species of bacteria and is the only bacteriocin approved for use as a food additive in the U.S. Commercial nisin production is very expensive and is, therefore, limited in its application in the food industry. Some factors that make commercial nisin production costly are slow nisin production rate and expensive fermentation medium requirement. Novel plastic composite supports (PCS), composed of equal parts polypropylene and agricultural products, were evaluated for its ability to produce nisin using a reduced nitrogen content media in biofilm reactors with or without pH control. Three reduced nitrogen content media: 1X, 0.5X, and 0.25X (10 g/L, 5 g/L, and 2.5 g/L yeast extract and peptone, respectively), were tested with equal parts of PCS rings and discs during duplicate 48 hour repeated-batch fermentations for nisin production and compared to a 1X suspendedcell control during pH controlled (6.8) and pH uncontrolled fermentations. Since previous studies have shown that PCS utilization lowers the nutrient requirement of the fermentation broth, it was anticipated that PCS can be used in the bioreactors to improve the production of nisin with less expensive medium using repeated-batch fermentation. However, results demonstrated that there was no increase in nisin production or productivity rates using the PCS with any reduced content medium over the 1X suspended-cell control during either pH condition. In spite of this, biofilm reactors have been successfully used to improve lactic acid and ethanol fermentations. The metabolism of nisin production and possible nisin absorption by L. lactis cells can be limiting factors which shadows the capability of PCS. The degradation or absorption is reducing the nisin level in the fermentation broth, and prevents biofilm to demonstrate higher nisin levels. Therefore, it is essential to find a fermentation protocol that prevents or minimizes the reduction in nisin level during fermentation. Then, biofilm reactors can be an effective method for nisin fermentation.