S Monfort

Defining treatment conditions for pulsed electric field pasteurization of apple juice

The influence of temperature and the presence of N(α)-lauroyl ethylester (ethyl lauroyl arginate, LAE) on the inactivation caused by continuous pulsed electric field treatments (PEF) in Escherichia coli O157:H7 suspended in apple juice have been investigated to define treatment conditions applicable at industrial scale that promote an equivalent safety level when compared with thermal processing. In the range of experimental conditions investigated (outlet temperature: 20-40 °C, electric field strength: 20-30 kV, treatment time: 5-125 μs) at outlet temperatures equal or lower than 55±1 °C, the inactivation of E. coli O157:H7 treated in apple juice ranged from 0.4 to 3.6 Log₁₀ cycles reduction and treated in apple juice supplemented with LAE (50 ppm) ranged from 0.9 to 6.7 Log₁₀ cycles reduction. An empirical mathematical model was developed to estimate the treatment time and total specific energy input to obtain 5 Log₁₀ cycles reduction in the population of E. coli O157:H7 suspended in apple juice supplemented with 50 ppm of LAE at different electric field strengths and inlet temperatures. Treatment conditions established for E. coli O157:H7 were validated with other PEF resistant Gram-positive (Listeria monocytogenes, and Staphylococcus aureus) and Gram-negative (Salmonella enterica serovar Typhimurium) strains. When the treatment was applied to the apple juice, a treatment of 25 kV/cm for 63 μs corresponding with an outlet temperature of 65 °C and input energy of 125 kJ/kg was required to achieve more than 5 Log₁₀ cycles in the four strains investigated. The addition of LAE reduced the treatment time required to obtain an equivalent inactivation (>5 Log₁₀ cycles) in the four microorganisms to 38.4 μs, the outlet temperature to 55 °C, and the input energy to 83.2 kJ/kg.

Evaluation of pulsed electric fields technology for liquid whole egg pasteurization.

This investigation evaluated the lethal efficiency of pulsed electric fields (PEFs) to pasteurize liquid whole egg (LWE). To achieve this aim, we describe the inactivation of Salmonella Enteritidis and the heat resistant Salmonella Senftenberg 775 W in terms of treatment time and specific energy at electric field strengths ranging from 20 to 45 kV/cm. Based on our results, the target microorganism for this technology in LWE varied with intensity of the PEF treatment. For electric field strengths greater than 25 kV/cm, Salmonella Enteritidis was the most PEF-resistant strain. For this Salmonella serovar the level of inactivation depended only on the specific energy applied: i.e., 106, 272, and 472 kJ/kg for 1, 2, and 3 Log(10) reductions, respectively. The developed mathematical equations based on the Weibull distribution permit estimations of maximum inactivation level of 1.9 Log(10) cycles of the target Salmonella serovar in the best-case scenario: 250 kJ/kg and 25 kV/cm. This level of inactivation indicates that PEF technology by itself cannot guarantee the security of LWE based on USDA and European regulations. The occurrence of cell damage due to PEF in the Salmonella population opens the possibility of designing combined processes enabling increased microbial lethality in LWE.

Design of a combined process for the inactivation of Salmonella Enteritidis in liquid whole egg at 55°C.

This paper is an evaluation of the lethal effectiveness of a successive application of pulsed electric fields (PEFs) and heat treatment in liquid whole egg (LWE) in the presence of different additives on the population of Salmonella serovar Enteritidis. Synergistic reductions of the Salmonella Enteritidis population were observed when LWE samples containing additives were treated with PEF (25 kV/cm; 100 and 200 kJ/kg), heat (55 °C), or PEF followed by heat. The presence of additives, such as 10 mM EDTA or 2% triethyl citrate, increased the PEF lethality 1 log₁₀ cycle and generated around 1.5 log₁₀ cycles of cell damage, resulting in the reduction of undamaged cells of 4.4 and 3.1 log₁₀ cycles, respectively. The application of PEF followed by heat treatment significantly (p < 0.05) reduced D(55 ºC) from 3.9 ± 0.2 min in LWE to 1.40 ± 0.06 min or 0.24 ± 0.02 min in the presence of 10 mM EDTA or 2% triethyl citrate, respectively. A PEF treatment of 25 kV/cm and 200 kJ/kg followed by a heat treatment of 55 °C and 2 min reduced more than 8 log₁₀ cycles of the population of Salmonella Enteritidis in LWE combined with 2% triethyl citrate, with a minimal impact on its protein soluble content. The heat sensitizing effect of PEF treatments in the presence of 2% triethyl citrate on the Salmonella population could enable LWE producers to reduce the temperature or processing time of thermal treatments (current standards are 60 °C for 3.5 min in the United States), increasing the level of Salmonella inactivation and retaining the quality of non-treated LWE.