Concentrações sensorialmente aceitas de óleo essencial de Mentha piperita L. em processos combinados para inibição de patógenos em sucos de frutas

Abstract

Mentha piperita L. essential oil (MPEO) has been proposed as a promising alternative to preserve fruits juices, however effective concentrations of MPEO may reach the consumer’s sensory rejection threshold. The combined application of EOs and mild heat (MH) or emerging technologies, such as pulsed electric field (PEF) and high hydrostatic pressure (HHP), has been reported as a strategic option for the incorporation of EOs into juices. Therefore, the aim of this study was to evaluate the combined application of sensorially accepted concentrations of MPEO with MH, PEF or HHP in the inhibition of pathogens in tropical fruit juices. In the first step of the study, the compromised acceptance threshold (CAT) and rejection threshold (RT) of MPEO were determined in cajá (Spondias mombim L.), guava (Psidium guajava L.) and mango (Mangifera indica L.) juices. The efficacy of MPEO concentrations below the RT againt Escherichia coli O157: H7 and Salmonella Enteritidis PT4 in these juices were evaluated alone and combined with MH (54 ºC; 8, 10 or 12 min). The effects of the combined application of MPEO and MH on the physical-chemical parameters of the studied juices were also evaluated. In the second step, the MPEO concentrations below RT were evaluated in nanoemulsions (n-MPEO) applied alone or combined with MH (50, 52 or 54 ° C), PEF (20, 25 or 30 kV/cm) and HHP (150, 200 or 300 MPa) against E. coli O157: H7 in guava and mango juices. The minimal inhibitory concentration of OEMP against E. coli O157: H7 and S. Enteritidis PT4 was 5.0 µL/mL. The CAT of MPEO was 0.30 µL/mL in cajá juice, 0.31 µL/mL in guava juice and 0.32 µL/mL in mango juice. The RT of MPEO was 1.36 µL/mL in cajá juice and 1.34 µL/mL in guava and mango juices. Only MPEO concentrations close or higher (= 1.25 µL/mL) than RT caused reductions of = 5 log10 CFU/mL in survival counts of E. coli O157:H7 and S. Enteritidis PT4 in in cajá, guava and mango juices. The combined use of MPEO concentrations below the RT (0.16, 0.31 or 0.63 µL/mL) and MH (54 ° C) caused a reduction = 5 log10 CFU/mL in counts of E. coli O157: H7 and S. Enteritidis PT4 in samejuices. The time to achieve the 5 log10 CFU/mL reduction of the initial population of pathogens decreased when the MPEO concentration used in combination with the MH increased. The MPEO combined with MH did not change the monitored physicochemical parameters in cajá, guava and mango juices. The n-MPEO (5.0 µL/mL) prepared by the emulsion phase inversion (EPI) method presented size < 200 nm, polydispersity index = 0.32, antimicrobial stability and efficacy against E. coli O157: H7 during 4 months storage. Compared to MPEO suspension (s-MPEO) at the same concentration, n-OEMP showed a greater long term antimicrobial efficacy in mango juice. In combination with MH, PEF and HHP, n- MPEO concentrations (0.16, 0.31 and 0.63 µL / mL) showed similar or greater efficacy than s- MPEO against E. coli O157: H7. The efficacy of combined treatment varied with the n-MPEO concentration, electric field intensity or applied temperature. The results indicate the use of MPEO concentrations (in suspension or nanoemulsion) below RT in combination with MH, PEF and HHP as feasible technologies for preservation of tropical fruit juices.