Partition of lactic streptococcal bacteriophage during the ultrafiltration concentration of milk and whey

Milk and whey inoculated with lactic streptococcal bacteriophages 316, or 322, or both were concentrated by UF using a DDS Mini-Lab 20. The plate and frame unit was fitted with Type GR61PP polysulfone membrane with a 20,000 molecular weight cutoff. The unit was operated at an inlet pressure of .40 MPa and an outlet pressure of .23 MPa with an initial flux of 2.0 to 3.0 L/h. Samples of retentate, permeate, and membrane were analyzed for the presence of bacteriophages. Under the conditions established in this study, phage particles did not pass through the membrane but instead became trapped in the polarization concentration layer or in the membrane. Phages were recovered from the membrane by extraction in sterile buffered water with the Stomacher. The UF concentration of milk containing the host species of Streptococcus cremoris resulted in phage propagation and lysis of the host but did not result in the passage of phages through the membrane. The UF processing of milk or whey should produce a phage-free permeate.