Contribution of high pressure and thyme extract to control Listeria monocytogenes in fresh cheese - A hurdle approach

Abstract

Abstract Capability of thyme natural antimicrobials (NAs) to reduce the intensity of high pressure processing (HPP) and enhance the inactivation of Listeria monocytogenes in fresh cheese was investigated. Thyme extracts were obtained by supercritical fluid extraction at 30 MPa and 40 MPa and their concentration was estimated in units of carvacrol (190.44–609.57 μg/mL). The acceptable sensorial threshold of thyme extract in cheese was 0.2% (v/w), a value lower than the MIC for L. monocytogenes. Detailed kinetic studies of L. monocytogenes inactivation in cheese were performed following HPP (200–300 MPa) treatments. A maximum 1.68-log10 CFU/g supplementary reduction was achieved for L. monocytogenes in cheese with HPP & NAs than without NAs. The kinetic parameter zp indicated an accelerated inactivation of L. monocytogenes when HPP was combined with thyme NAs, as hurdle applied to fresh cheese (55.99 MPa for HPP and 33.29 MPa for HPP with thyme NAs). Industrial relevance Applied as a post-processing treatment high pressure processing (HPP) is considered an effective listericidal tool that produces limited quality changes in foods compared to other preservative methods. In order to overcome the main drawback related to HPP effect on cheese structure, a combination of pressure with natural antimicrobials (NAs) is proposed for reducing the intensity of processing while improving microbiological safety of food. The efficacy of L. monocytogenes inactivation in cheese by HPP and HPP with NAs from thyme was kinetically evaluated and modeled in the present work. The current results provide support for the industrial development of more effective combined HPP with NAs treatment, able to minimize the risk of Listeria presence in cheese.