Eficácia de óleos essenciais de Citrus spp. aplicados isolados ou em combinação com tratamento térmico moderado no controle de bactérias autóctones deteriorantes em sucos de frutas

Abstract

Citrus lemon (CLEO) and C. reticulata essential oils (CREO) have antimicrobial activity against spoilage bacteria of fruit juices. A limiting factor in the application of these substances as preservatives in fruit juices is that the effective concentrations typically exceed the limit of sensory acceptance of consumers. This study assessed the application of sensorially accepted concentrations of CLEO and CREO alone or in combination with mild heat treatment (MHT) against spoilage bacteria isolated from apple and orange juices. Initially, were determined the compromised acceptance threshold (CAT) and rejection threshold (RT) of CLEO and CREO in apple and orange juices. The concentrations of CLEO and CREO (0.13, 0.25 e 0.50 μL/mL), below the RT, were assessed alone and in combination with MHT (54 ºC, 0, 2, 4, 6, 8, 10 and 12 min) against Lactobacillus brevis, L. plantarum and Leuconostoc mesenteroides isolated from apple and orange juices. The effects of the combined application of CLEO and CREO with MHT on the physical-chemical parameters (total soluble solids, pH and titratable acidity) of the juices were assessed after 12 min exposure. The concentration 0.50 μL/mL of CLEO and CREO alone or in combination with MHT was assessed the effects on physiological functions of L. brevis and L. mesenteroides in orange juice using flow cytometry. The minimal inhibitory concentration of CLEO and CREO against L. brevis, L. plantarum e L. mesenteroides was 2.0 μL/mL. The CAT of CLEO and CREO varied from 0.15 to 0.17 μL/mL in apple and orange 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. All concentrations of CLEO or CREO below the RT 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. A reduction of approximately 5 log10 CFU/mL was observed in the counts of L. brevis, L. plantarum e L. mesenteroides after 12 min of exposure to 0.50 μL/mL CLEO or CREO in combination with MHT in apple and orange juices. Effective combinations of CLEO or CREO with MHT against the test strains did not compromise the quality parameters of apple and orange juices. The extension of damage on physiological functions varied between CLEO and CREO, the tested strains and depended on the exposure time in orange juice. CREO alone or combined with MHT caused permeabilisation, depolarisation and compromised the respiratory and efflux activity in a percentage cells of L. mesenteroides than L. brevis cells, while the opposite was observed for CLEO. The highest percentage (up to 99%) of cells permeabilised, depolarised and with compromised respiratory and efflux activity were always observed in combined treatments, regardless the time of exposure or strain tested. The results obtained in this study indicate the application fo sensorially accepted concentrations of CLEO and CREO in combination with MHT as feasible technologie in spoilage bacteria control of fruit juices.