91E-3 |
Listeria innocua inactivation kinetics in whole milk by high pressure |
J. WELTI-CHANES1, M. Correa-Balderas2, E. Palou2, A. López-Malo2, and G. V. Barbosa-Cánovas3. (1) Departamento de Ingeniería Química y Alimentos, Universidad de las Américas-Puebla, Sta. Catarina Mártir, Cholula, Puebla, 72820, Mexico, (2) Mexico, (3) Biological Systems Engineering Department, Washington State University, Pullman, WA A special interest in food processing with high pressure (HP) as an alternative to heat treatments is enhanced due to the reported beneficial aspects on quality attributes and unique physical and sensory characteristics of pressure processed foods and the effects of HP in biological systems, especially the microbial inactivation. For a broader use of HP in food processing, it is of special interest to determine the process conditions for pressure pasteurization in view of industrial applications. High pressure inactivation kinetics of Listeria innocua in whole milk were determined at 21°C and pressures from 345 to 448 MPa. Kinetic analysis was also done. Whole milk was inoculated with 106 cfu/mL and subjected to HP treatments in a isostatic pressure machine. Viable bacteria number was determined by surface platting after each treatment onto Oxford agar plates. Logarithmic representation of the survival fraction were statistically analyzed, (ANOVA) determining the significance of pressure level. The come up time to reach a pressure exerts an important effect on the survival fraction of L. innocua. Bacteria cells inactivation followed first order reaction kinetics, with inactivation rates and decimal reduction times that varied from 0.5 to 1.8 min-1 and from 4.7 to 1.3 min, respectively. The pressure dependence of the yeast inactivation rates can be described by the apparent activation volume (D V*) and by a "pressure z value (zp)", revealing a D V* of -35.4 cm3 mol-1 and zp of 161 MPa. To increase microbial safety and assure microbial stability of foods processed by HP, the pressure treatment must ensure a satisfactory reduction in the initial microbial counts, thus kinetic analysis and the pressure dependence of microbial inactivation rates are useful to scale-up industrial applications.
Session 91E, Nonthermal Processing: Nonthermal processing of foods
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