Evaluation of an Inoculation System for a Closed Bulk Starter Vessel1

Abstract

Stainless steel vessels (open, closed and control, i.e. not exposed to aerosol) containing 10% reconstituted nonfat dry milk were inoculated with Streptococcus cremoris at 106 CFU/ml. Milk in the closed vessel was specifically inoculated through a rubber seal in a port using a sterile needle and syringe in the presence of an aerosol containing bacteriophage, Escherichia coli and milk or whey solids. The lid of the open vessel was removed for 2 min to expose milk to the aerosol. Milk was incubated at 22°C for 16 h. Samples were tested for pH, titratable acidity, and E. coli, host and bacteriophage numbers. E. coli and bacteriophage were recovered from the open vessel, and not the control and closed vessels. This inoculation system minimized exposure of bulk starter medium to an aerosol and reduced the risk of producing bulk starter contaminated with bacteriophage.