Influence of milk aeration on growth of psychrotrophic pseudomonads

The psychrotrophic microflora of raw milk from a Cornell University herd was examined and the three most frequently occurring isolates ( Pseudomonas species) were subjected to oxygen concentrations of 1 to 12 ppm and temperatures of 3 to 9°C in growth studies in raw milk. At 3°C, a reduction in oxygen level from 9-12 to 1-3 ppm resulted in a 63% increase in generation time for Pseudomonas fluorescens . However, the reduction in growth temperature from 9 to 3°C at 9-12 ppm oxygen produced a 280% generation time increase for P. fluorescens . Similar observations were made for the other isolates. An analysis of variance revealed a significant interaction between the effects of oxygen and temperature on growth of the isolates.