Use of Azadirachta indica extract in the control of contaminant bacteria in fermentation processes

Abstract

Considering that gram-positive contaminant bacteria may compromise the alcoholic fermentation process for ethanol production, natural biocides are sought for use in controlling such microorganisms. In this sense, neem (Azadirachta indica), known for its biological properties, emerges as a solution for controlling these contaminations. This study aimed to evaluate the antimicrobial activity of neem leaf, bark, and seed extracts, correlating them to the presence of secondary metabolites, thus determining their biocide potential. The extracts were obtained by maceration in ethanol and phytochemically analyzed through thin-layer chromatography (TLC) and Fourier transform infrared spectroscopy (FTIR), with the quantification of total phenolics, total flavonoids, total tannins, and antioxidant activity. The antimicrobial activity was evaluated through disk diffusion tests and the minimum inhibitory concentration (MIC) determination, using L. fermentum and L. mesenteroides as bacterial models. The tests showed that the leaf and bark extracts inhibited bacterial growth without affecting the yeast S. cerevisiae, with an efficacy of 50 and 30 mg/mL, respectively. A phytochemical analysis revealed the predominance of flavonoids in the leaves and a more significant concentration of tannins in the bark, both of which are recognized for their antimicrobial properties. The extracts also presented high levels of phenolic compounds, reinforcing their bacterial efficacy, while the antioxidant activity of the bark suggests a complementary role of action of the extract. The seed extract did not show antimicrobial activity. Hence, the neem leaf and bark extracts have biocide potential to be used in alcoholic fermentation.