Seleção de bactérias ácido láticas e estudo quanto ao potencial antimicrobiano frente a leveduras deteriorantes no processo vinícola

Abstract

Winemaking is a complex biotechnological process that involves microbiological and physicochemical transformations essential to produce quality wines. However, the presence of spoilage yeasts, such as Dekkera bruxellensis and Saccharomycodes ludwigii, represents a significant challenge for the wine industry, since these microorganisms produce undesirable compounds that alter the sensory profile and compromise the stability of the product. Traditionally, the control of these contaminations is carried out by the addition of sulfur dioxide (SO₂), due to its antimicrobial and antioxidant properties. However, the continuous use of SO₂ has been questioned due to concerns related to the health of sensitive consumers and the growing demand for natural wines with less chemical intervention. In this context, lactic acid bacteria (LAB) emerge as a promising alternative, due to their natural role in malolactic fermentation and their potential production of antimicrobial compounds, such as organic acids, hydrogen peroxide, and bacteriocins. The present study aimed to evaluate the antimicrobial potential of LAB isolates against the yeasts D. bruxellensis and S. ludwigii, seeking to identify cultures with possible application as bioprotective agents in winemaking. Initially, 21 bacteria were isolated from grape fermentate, but the isolates showed exclusively anaerobic growth, making their use unfeasible. Thus, in total, 21 previously obtained isolates from different matrices, such as grape, kefir, rejuvelac, natural yogurt, and pickled cucumber, were used. Morphological and biochemical analyses confirmed that the isolates were Gram-positive, non-sporulating, and catalase-negative, characteristics typical of LAB. The bacilli showed heterofermentative metabolism, while the cocci were homofermentative, with 12 isolates compatible with the Enterococcus genus. In the safety tests, 16 isolates showed a γ-hemolytic profile, indicating the absence of hemolytic activity, which makes them safe for biotechnological applications. The evaluation of tolerance under oenological conditions demonstrated that 15 LAB were able to grow at pH 3, in the presence of 13% (v/v) ethanol and 300 mg/L of free SO₂, revealing high resistance to conditions typical of the wine environment. On the other hand, none of the isolates grew in minimal medium, showing the nutritional requirement of these bacteria. The antagonism assays, carried out by the disk-diffusion and spot-on-the-lawn methods, did not show inhibition zones against the spoilage yeasts tested, indicating that, under the evaluated conditions, the metabolites produced were not able to interfere with yeast growth. These results suggest that, although LAB show resistance and adaptation to wine conditions, their antimicrobial action may depend on specific environmental factors, such as incubation time, medium composition, and direct cell interaction. As a future perspective, it is recommended to evaluate the antagonistic potential of the isolates against spoilage bacteria, such as Acetobacter aceti, which also represent a risk to wine stability.