RESUMO: Escherichia coli O157:H7 é um sorotipo toxigênico de E. coli associado mundialmente a surtos de doenças alimentares causadas por produtos cárneos. Os sais de cura são normalmente empregados como antimicrobianos na fabricação de linguiças, entretanto, possuem pouco efeito inibitório sobre enterobactérias como E. coli. Devido à crescente demanda por produtos naturais, o uso de óleos essenciais tem sido proposto como antimicrobiano natural em alimentos. O objetivo deste estudo foi avaliar os efeitos do óleo essencial de alho (GO) e isotiocianato de alila (AITC) contra E. coli O157:H7 in vitro e em linguiça. As concentrações inibitória mínima (MIC) e bactericida mínima (MBC) dos óleos, isolados e em combinação, contra E. coli O157:H7 foram determinadas in vitro. Lotes de linguiça foram inoculados com 8log UFC/g E. coli O157:H7 e diferentes concentrações de GO + AITC e estocados a 6°C por 20 dias. Contagens de E. coli O157:H7 e determinação de cor instrumental (L*, a*, b*, C* e hue) foram realizadas a cada 5 dias. Nos testes in vitro, AITC mostrou maior ação inibitória que GO, havendo efeito sinérgico dos óleos quando combinados. Os tratamentos T3 e T4 mostraram redução de 1,01log UFC e 1,87log UFC de E. coli O157:H7 comparados ao controle. A intensidade de cor vermelha e a saturação de cor aumentaram durante a estocagem nas linguiças adicionadas de óleos essenciais. A adição dos óleos GO + AITC causou mínima alteração no sabor e na aparência das linguiças e foi capaz de reduzir a população de E. coli O157:H7 no produto cárneo, mostrando potencial para uso como conservante natural nesse tipo de alimento.

ABSTRACT: Escherichia coli O157:H7 is a toxigenic serotype of E. coli and has been associated with foodborne outbreaks involving meat products, vegetables and fresh produces worldwide. Salts for curing are usually employed as antimicrobials in the production of pork sausages. However, salts do not have a significant inhibitory effect on enterobacteria. Due to the growing demand for natural foods, the use of essential oils has been proposed as natural antimicrobials in food. This study aimed to evaluate the effects of garlic essential oil (GO) and allyl isothiocyanate (AITC) against E. coli O157:H7 in vitro and in pork sausage. The Minimal Inhibitory Concentration (MIC) and Minimal Bactericidal Concentration (MBC) of these oils, alone and in combination, against E. coli O157:H7 were determined. Pork sausage was inoculated with 8log CFU/g E. coli O157:H7 and different combinations of GO and AITC. A control group was performed without essential oils. Sausages were packaged and stored at 6°C for 20 days. E. coli O157:H7 population and instrumental color (L*, a*, b*, C* and hue) determinations were performed at 5-day intervals. AITC showed lower MIC and MBC than GO. When combined, AITC and GO showed a synergistic effect. Treatments T3 and T4 showed 1,01log CFU and 1,87log CFU reduction of E. coli O157:H7 compared to control. The redness and the chroma of sausages treated with AITC and GO increased during storage. Together, GO and AITC caused minor changes in taste and flavor of sausages, and were able to reduce the population of E. coli O157:H7 and to maintain the red color of sausage during storage.

The antimicrobial activity of a methanolic extract of amurca (olive oil lees) was determined against both Gram-positive (L. monocytogenes and S. aureus) and Gram-negative (E. coli O157:H7 and S. enteritidis) foodborne pathogens at 10 °C or 37 °C using microdilution and disk diffusion methods, and its relative activity was compared to selected antibiotics. Minimum inhibitory (MIC) and minimum bactericidal (MBC) concentrations of amurca extract ranged from 60 to 80 µl/ml at 37 °C after 24 h against all tested strains. At 10 °C, amurca was more inhibitory with MIC and MBC values of 40 and 60 µl/ml, respectively, after 7 d against tested strains. Amurca at 40 µl/ml reduced numbers of tested pathogens by 2.5 to 3.2 log10 CFU/ml at 10 °C after 7 d, but was not inhibitory at 37 °C after 24 h. Protein prepared from amurca was not antimicrobial. The relative antimicrobial activity (inhibition zone ratio) of 80 µl/ml amurca methanolic extract compared to chloramphenicol, erythromycin, gentamycin and tetracycline ranged from 0.36 to 1.0 against Gram-negative and from 0.45 to 2.0 against Gram-positive bacteria. In addition, amurca extract inhibited E. coli O157:H7 02-0628 and S. aureus 26127 which were resistant to tetracycline and chloramphenicol, respectively.