Pseudomonas spp. and Hafnia alvei growth in UHT milk at cold storage

Gram-negative psychrotrophic bacteria isolated from samples of spoiled commercial ultra-heat treated (UHT) milk from Taiwan were comprised of 67% Pseudomonas spp. and 22% Enterobacteriaceae. Whole milk, low-fat milk, and flavored milk samples were tested. The modified Gompertz equation was used to model the data and provided a good fit for the growth of Pseudomonas spp. and Hafnia alvei at 7 °C for 14 days in both whole UHT milk and low-fat UHT milk. From this model, the estimated lag time for H. alvei was longer than that for Pseudomonas fluorescens in both whole UHT milk and low-fat UHT milk. The growth rate of H. alvei was higher than that of P. fluorescens. The pH value was significantly reduced by H. alvei than P. spp. after cultured in whole and low-fat UHT milk at 7 °C for 14 days.