Kinetics of destruction ofEscherichia coliandPseudomonas fluorescensinoculated in ewe's milk by high hydrostatic pressure

Abstract

Ewe's1999199919991999 Academic PressAcademic PressAcademic PressAcademic Pressmilk standardized to 6% fat was inoculated with Escherichia coliand Pseudomonas fluorescensat a concentration of 107and 108cfuml−1respectively, and treated by high hydrostatic pressure. Treatments consisted of combinations of pressure (50-300MPa), temperature (2, 10, 25 and 50°C), and time (5, 10 and 15min). Violet red bile agar and crystal-violet-tetrazolium count were used to determineE. coliandP. fluorescensrespectively. Pressurization at low and moderately high temperatures produced higher P. fluorescensinactivation than treatments at room temperature, while pressurization at only moderately high temperature produced high E. coliinactivation; low and room temperatures produced similar reductions. On E. coli,reductions of 6.055log units were produced with 300MPa for 15min at 50°C, while on P. fluorescens,reductions of 5.059log units were produced with 250MPa for 15min at 50°C. Both micro-organisms showed a first-order kinetics of destruction in the range 0-30min, with D-values (at different temperatures and pressures from 150 to 300MPa) between 2.055 and 18.058min for E. coli,and 2.058-23.053min for P. fluorescens.Abaroprotective effect of ewe's milk (6% fat) on both micro-organisms was observed, in comparison with other studies using different means and similar pressurization conditions.