Reduction of Lactococcus lactis phage contamination in whey by means of membrane filtration: Impact of phage morphology and of bacterial host cells functioning as “phage fishing tool”

For dairy bacteriophages, the impact of phage morphology and whey components on phage retention efficiencies in filtration processes is not known. Therefore, the influence of (i) five differently shaped Lactococcus lactis phages as well as (ii) differently treated bacterial host cells added to native whey were analysed via cross-flow membrane filtration experiments with polyethersulfone membranes. Filtration efficiency with respect to phage retention and whey protein permeation was investigated. Compared with untreated native whey, phage retention was significantly higher (up to 4.8 log units) in the experiments using whey that was spiked with mechanically disrupted lactococcal host cells. However, the retention of phages commonly found in the dairy environment (i.e., members of the 936, c2, and P335 phage groups) did not correlate with the phage morphology. Results of this model study clearly demonstrate that phage titres can be reduced in whey (containing a sufficient protein concentration) by flat sheet membrane filtration processes.