RESUMO
This study investigated physiological alterations involved in the inactivation of Levilactobacillus (L.) brevis and Leuconostoc (Lc.) mesenteroides in orange juice caused by Citrus lemon essential oil (CLEO) and C. reticulata essential oil (CREO) alone and combined with mild heat treatment (MHT). Damage in DNA, membrane integrity, membrane potential, metabolic and efflux activity of bacterial cells were measured after exposure (6 and 12 min) to CLEO or CREO (0.5 µL/mL) and/or MHT (54 °C) using flow cytometry. Limonene was the major constituent in CLEO (66.4%) and CREO (89.4%). The size of the damaged cell subpopulations increased (p < 0.05) after longer exposure time and varied with the tested essential oil and/or bacterial isolate. After exposure to CLEO and CREO alone, the cell subpopulations with damage in measured physiological functions were in a range of 19.6-66.8% and 23.8-75.9%, respectively. Exposure to CREO resulted in larger Lc. mesenteroides cell subpopulations (35.4-68.7%) with damaged DNA, permeabilized and depolarized membrane and compromised metabolic or efflux activity compared to L. brevis (23.8-58.0%). In contrast, exposure to CLEO led to higher damaged L. brevis cell subpopulations (35.1-77%) compared to Lc. mesenteroides (25.3-36.6%). Exposure to combined treatments (CLEO or CREO and MHT) affected the measured physiological functions in almost the entire L. brevis and Lc. mesenteroides cell population (up to 99%), although the damage extension on each isolate varied with tested essential oil. Results show that inactivation of L. brevis and Lc. mesenteroides cells caused by CLEO and CREO alone and combined with MHT in orange juice involves a multi-target action, which causes DNA damage, altered permeability and depolarization of membrane and compromised metabolic and efflux activities.
Assuntos
Citrus/química , Sucos de Frutas e Vegetais/microbiologia , Temperatura Alta , Lactobacillales/fisiologia , Óleos Voláteis/farmacologia , Pasteurização/métodos , Membrana Celular/efeitos dos fármacos , Membrana Celular/metabolismo , Membrana Celular/efeitos da radiação , Dano ao DNA , Microbiologia de Alimentos , Lactobacillales/classificação , Lactobacillales/efeitos dos fármacos , Lactobacillales/efeitos da radiação , Óleos Voláteis/química , Fatores de TempoRESUMO
This study assessed the compromised acceptance threshold (CAT) and rejection threshold (RT) of Citrus lemon (CLEO) and Citrus reticulata essential oil (CREO) in apple and orange juices. The efficacy of CLEO and CREO concentrations below the RT were evaluated alone and combined with mild heat treatment (MHT) (54 °C, up to 12 min) to inactivate the autochthonous spoilage bacteria Lactobacillus brevis, Lactobacillus plantarum, and Leuconostoc mesenteroides in apple and orange juices. The CAT of CLEO and CREO varied from 0.15 to 0.17 µL/mL in orange and apple juices. The RT of CLEO was approximately 0.58 µL/mL in apple and orange juices, and the RT of CREO was 0.68 µL/mL in both juices. When CLEO and CREO were assayed alone, the highest concentration (0.50 µL/mL) decreased counts of all strains approximately 2 log10 CFU/mL after 12 min of exposure to 54 °C. All concentrations of CLEO or CREO in combination with MHT acted synergistically against L. brevis, L. plantarum, and L. mesenteroides. Decreases in counts varied with the strain, CLEO and CREO concentrations, juice type, and exposure time to the combined treatment. CREO was more effective than CLEO in combination with MHT against the strains in apple and orange juices. Effective combinations of CLEO or CREO with MHT to control the autochthonous spoilage bacteria did not compromise the quality parameters (°Brix, pH, and titratable acidity) that characterize unsweetened juices. These results indicate CLEO or CREO at concentrations below the sensory RT in combination with MHT as a feasible technology to control autochthonous spoilage bacteria in fresh fruit juices. PRACTICAL APPLICATION: The present study provides novel information concerning the efficacy of sensorially accepted doses of CLEO and CREO combined with MHT against autochthonous spoilers in fruit juice. The valuable synergistic effects that can be observed when combining CLEO and CREO with MHT reveal a feasible preservation technology and alternative to traditional treatments that are successful because they help reduce treatment intensity, thereby avoiding adverse effects on the sensory, physicochemical, and nutritional properties of these products.
Assuntos
Citrus/microbiologia , Sucos de Frutas e Vegetais/microbiologia , Lactobacillales/classificação , Malus/microbiologia , Óleos Voláteis/farmacologia , Óleos de Plantas/farmacologia , Citrus/química , Conservação de Alimentos/métodos , Temperatura Alta , Lactobacillales/efeitos dos fármacos , Lactobacillales/fisiologia , Malus/química , Óleos Voláteis/química , Óleos de Plantas/químicaRESUMO
This study assessed the inhibitory effects of the essential oil from Origanum vulgare L. (OVEO) on Staphylococcus aureus, Listeria monocytogenes, and a mesophilic starter coculture composed of lactic acid bacteria (Lactococcus lactis subsp. lactis and L. lactis subsp. cremoris) in Brazilian coalho cheese systems. The MIC of OVEO was 2.5 µl/ml against both S. aureus and L. monocytogenes and 0.6 µl/ml against the tested starter coculture. In cheese broth containing OVEO at 0.6 µl/ml, no decrease in viable cell counts (VCC) of both pathogenic bacteria was observed, whereas the initial VCC of the starter coculture decreased approximately 1.0 log CFU/ml after 24 h of exposure at 10°C. OVEO at 1.25 and 2.5 µl/ml caused reductions of up to 2.0 and 2.5 log CFU/ml in S. aureus and L. monocytogenes, respectively, after 24 h of exposure in cheese broth. At these same concentrations, OVEO caused a greater decrease of initial VCC of the starter coculture following 4 h of exposure. Higher concentrations of OVEO were required to decrease the VCC of all target bacteria in semisolid coalho cheese slurry compared with cheese broth. The VCC of Lactococcus spp. in coalho cheese slurry containing OVEO were always lower than those of pathogenic bacteria under the same conditions. These results suggest that the concentrations of OVEO used to control pathogenic bacteria in semihard cheese should be carefully evaluated because of its inhibitory effects on the growth of starter lactic acid cultures used during the production of the product.
Assuntos
Queijo/microbiologia , Aditivos Alimentares/farmacologia , Lactococcus/crescimento & desenvolvimento , Listeria monocytogenes/efeitos dos fármacos , Óleos Voláteis/farmacologia , Origanum/química , Staphylococcus aureus/efeitos dos fármacos , Animais , Brasil , Bovinos , Ácido Láctico/metabolismo , Lactococcus/metabolismo , Listeria monocytogenes/crescimento & desenvolvimento , Viabilidade Microbiana/efeitos dos fármacos , Leite/microbiologia , Staphylococcus aureus/crescimento & desenvolvimentoRESUMO
In the present study, we assessed the effects of Thymus vulgaris L. essential oil (TVEO) on Staphylococcus aureus and Listeria monocytogenes, pathogenic bacteria frequently associated with fresh or low-ripened cheeses (e.g., Brazilian coalho cheese), and on a starter co-culture comprising Lactococcus lactis subsp. lactis and L. lactis subsp. cremoris, which are commonly used for the production of different cheeses. To measure these effects, we determined the minimum inhibitory concentration (MIC) and assessed bacterial cell viability over time in (coalho) cheese-based broth and in a semi-solid (coalho) cheese model at 10 °C. The MIC for TVEO was 2.5 µL/mL against S. aureus and L. monocytogenes, while the MIC was 1.25 µL/mL against the starter co-culture. The TVEO (5 and 2.5 µL/mL) sharply reduced the viable counts of all assayed bacteria in cheese broth over 24 h; although, at 5 µL/mL, TVEO more severely affected the viability of the starter co-culture compared with pathogenic bacteria. The addition of 1.25 µL/g of TVEO in the semi-solid cheese model did not reduce the viable counts of all assayed bacteria. At 2.5 µL/g, TVEO slightly decreased the viable counts of S. aureus, L. monocytogenes and Lactococcus spp. in the semi-solid cheese model over 72 h. The final counts of Lactococcus spp. in a semi-solid cheese model containing 2.5 µL/mL TVEO were lower than those of pathogenic bacteria under the same conditions. These results suggest that the doses of TVEO used to control pathogenic bacteria in fermented dairy products, especially in low-ripened cheeses, should be cautiously considered for potential negative effects on the growth and survival of starter cultures.