Inactivation of Listeria monocytogenes and Listeria innocua in yogurt drink applying combination of high pressure processing and mint essential oils

Influences of high pressure processing (HPP) on some physical properties and on inactivation of Listeria monocytogenes and Listeria innocua in a yogurt drink (ayran) were quantified with or without addition of mint essential oil. Pressure treatment alone or combined with mint essential oil did not cause significant changes in pH, water activity, color and serum protein separation (p > 0.05). HPP of ayran samples at 600 MPa for treatment time of 300 s reduced L monocytogenes and L innocua by more than 5-log units (p <= 0.05) at ambient temperature. Addition of mint essential oil further enhanced inactivation of both bacteria by more than 1 log cfu mL(-1). Combination of mint essential oil with HPP provided a reduction in pressure treatment severity by 100-300 MPa or by 210 s to achieve the same amount of inactivation relative to HPP alone. Both Weibull distribution and log-logistic models were fitted to survival data. High pressure-processing combined with mint essential oil appeared to be a promising technique for preserving microbiologically-safe ayran with no significant impacts to product quality. (C) 2011 Elsevier Ltd. All rights reserved.