ABSTRACT: This study evaluated the effects of potassium and sodium carbonate and bicarbonate, Bacillus subtilis (Cohn, 1872) QST-713, Bacillus pumilus (Meyer & Gottheil, 1901) QST-2808, and crude and roasted coffee oils on the inhibition of mycelial growth and conidial germination in Botrytis cinerea Pers.: Fr and the colonization of begonia (Begonia elatior Hort. ex Steud) leaf discs by B. cinerea inoculated before, simultaneously and after with these alternative products. The assays were carried out using the Baladin begonia cultivar. The inhibition of B. cinerea mycelial growth and conidial germination was proportional to increases in the concentration of all the products. The inhibition of conidial germination was directly proportional to the concentrations of B. pumilus QST-2808 and B. subtilis QST-713. Coffee oils were less efficient in inhibiting germination than the other products. The crude and roasted coffee oils, potassium and sodium carbonates and bicarbonates, and B. pumilus and B. subtilis sprayed 24 h before, simultaneously, or 24 h after pathogen inoculation inhibited the colonization of begonia leaf discs by B. cinerea. The positive results for the suppression of B. cinerea by the alternative products tested herein merit scrutiny. There is a pressing need to evaluate these products in the management of gray mold, as the severity of this disease is usually high under favorable conditions in greenhouses.

RESUMO Óleos essenciais de espécies vegetais são fontes alternativas importantes de compostos antimicrobianos no combate a patógenos de importância alimentar. O presente estudo buscou avaliar a atividade antimicrobiana in vitro do óleo essencial de tomilho (Thymus vulgaris), e aplicá-lo na sanitização de rúcula (Eruca sativa) minimamente processada, visando ao aumento da segurança e da vida útil desta hortaliça. A atividade antibacteriana in vitro foi avaliada através dos ensaios de difusão em disco, determinação da concentração mínima inibitória (CMI) e da concentração mínima bactericida (CMB) frente a diferentes espécies bacterianas de importância em alimentos. Foi realizado um teste desafio de aplicação do óleo essencial de tomilho (0,2%) na sanitização de rúcula inoculada com Escherichia coli (3 Log UFC mL-1), em comparação com o hipoclorito de sódio (120 ppm de cloro ativo). Posteriormente, foi conduzido um experimento de aplicação do óleo essencial (0,2%) como sanitizante em rúcula minimamente processada para a avaliação da vida útil desta hortaliça, armazenada a 8 °C durante 7 dias. Periodicamente, foi realizada a contagem de microrganismos aeróbios mesófilos, determinação do pH, acidez total e avaliação da cor das amostras. O óleo essencial de tomilho apresentou forte atividade antimicrobiana in vitro, frente a todas as espécies de bactérias testadas (CMIs entre 0,075 e 0,62 mg mL-1). Nos experimentos in situ, o óleo essencial de tomilho (0,2%) e o hipoclorito de sódio (120 ppm de cloro ativo) não foram eficientes na eliminação de E. coli inoculada em rúcula minimamente processada, não resultando na extensão da vida útil deste produto, em comparação ao controle (p>0.05). Entretanto, a taxa de incremento da população de E. coli ao longo do tempo foi menor nas amostras de rúcula sanitizadas com a solução à base de óleo essencial de tomilho (0,2%), denotando um efeito positivo deste óleo essencial, que pode ser otimizado com futuras adequações de concentração e tempo de imersão durante a sanitização de rúcula.

ABSTRACT Essential oils from plants are an important alternative source of antimicrobial compounds against important pathogens for food safety. This study aimed to evaluate the in vitro antimicrobial activity of thyme essential oil (Thymus vulgaris) and to apply it in the sanitization of minimally processed arugula (Eruca sativa), aiming to increase the safety and shelf life of arugula. The in vitro antibacterial activity of the essential oil was evaluated by disc diffusion assays and determining the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against different foodborne pathogens. Thereafter, a “challenge test” was carried out to evaluate the antibacterial activity of the thyme essential oil (0.2%) on the sanitization of arugula inoculated with Escherichia coli (3 log CFU mL-1) compared to sodium hypochlorite (120 ppm of active chlorine). Afterwards, an experiment of applying the thyme essential oil (0.2%) as a sanitizing agent in minimally processed arugula was carried out to evaluate the vegetable shelf life compared to sodium hypochlorite (120 ppm of active chlorine). The arugula was stored at 8 °C for 7 days, and periodically, the number of aerobic mesophilic microorganisms, pH and titratable acidity were determined, and the color of the samples was evaluated. The thyme essential oil had strong antimicrobial activity in vitro against all species of bacteria tested. In the experiments in situ, the thyme essential oil (0.2%) and sodium hypochlorite (120 ppm of active chlorine) were not efficient in eliminating the inoculated E. coli from minimally processed arugula, and they did not result in an extension of the shelf life of the arugula in comparison to the control (p>0.05). However, the growth rate of the E. coli population over time on the arugula samples sanitized with the thyme essential oil (0.2%) was low, which indicates a positive effect of the essential oil, which may be optimized with future adjustments in the concentration and immersion time for the arugula sanitization.