TEMPORARY REMOVAL: Application of essential oils as natural antimicrobials in lactic acid bacteria contaminating fermentation for the production of organic cachaça

Abstract

Sugarcane-based fermentation is an essential process for different sectors of economic importance, such as the food industry with fermented and distilled beverages. However, this process can suffer from high contamination by wild yeasts and bacteria, especially lactic acid bacteria (LAB). This makes it necessary to use decontamination strategies and search for new methods that have a low environmental impact and contribute to the production of organic products. Among the options, oregano and thyme essential oils stand out for their antibacterial compounds. The aim of this study was to use oregano and thyme essential oils as natural antimicrobials in the alcoholic fermentation of sugar cane juice. Initially, the minimum inhibitory concentration of the essential oils in the fermentation was assessed through turbidity in the sensitivity test, which allowed us to determine which concentrations of essential oils would inhibit the contaminants, 3 morphologically selected LAB strains, as well as assessing the viability of CA-11. For LAB, 3 concentrations of each essential oil were tested, ranging from 0.1 to 0.4 μL/mL, while for CA-11 it was 0.06, to 0.1 μL/mL. The results indicated a maximum total value of essential oils per mL of 0.06 μL. Based on this result, a 24-1 fractional factorial was established, with 8 conditions +3 central points, with 4 variables, oregano essential oil (0, 0.03 and 0.06 μL/mL), thyme (0, 0.03 and 0.06 μL/mL), initial soluble solids (14, 16 and 18°Brix) and initial yeast concentration (2.5, 3 and 3.5 g/L), with the temperature set at 32 °C for a period of 12 h. The results showed that the center point condition with 0.03 μL/mL of oregano EO, 0.03 μL/mL of thyme controlled the proliferation of contaminating bacteria compared to the control condition. In the experimental validation, the treatment with essential oils had a lower final population of LAB (5.95 log) than the final population of the control treatment (6.53 log), and it was also observed that the treatment with EOs had an alcohol production around 3 % higher than the treatment without antimicrobials. The experimental validation phase confirmed the synergistic action of oregano and thyme essential oils in controlling the proliferation of contaminating bacteria. In conclusion, it was possible to determine the synergistic antimicrobial action of essential oils against LAB during alcoholic fermentation based on organic sugar cane.