Concentration and recovery of the bacteriocin nisin from Lactococcus lactis subsp. lactis.

Abstract

This investigation compared various techniques to concentrate and recover nisin from Lactococcus lactis cells. Centrifugation, combined with pH manipulation, was initially investigated as it is known that nisin will adsorb to producer cells at pH 6.5 and desorb at pH < or = 3.0. Unfortunately, centrifugation stripped producer cells of nisin even at pH 6.5; therefore a milder separation process (microfiltration) was evaluated. Results using a medium (LTB) containing peptone, tryptone, yeast extract, NaCl, Na2HPO4 and glucose demonstrated that nisin could be at least partially concentrated with cells via microfiltration. However, when a filtered stillage-based medium was used, nisin production was boosted to levels which exceeded the holding capacity of producer cells, resulting in release of nisin from cells at pH 6.5. Since it appears unfeasible to use producer cells for nisin recovery, an alternative may be to separately immobilize cells/ fragments in a re-usable column to act as a "resin' to adsorb nisin. Microfiltration could then be used to release nisin from cells, with nisin recovered by passing the permeated material through the immobilized-cell columns at pH 6.5.