ANTIMICROBIAL ACTIVITY OF Psidium guajava LEAF HYDROLATES AGAINST PATHOGENIC AND PROBIOTIC MICROORGANISMS

Hydrolates, by-products of essential oil extraction, contain water-soluble compounds with antimicrobial potential and applications in functional foods. This study evaluated the effect of three Psidium guajava (guava) leaf hydrolates (H1, H2, and H3), obtained by hydrodistillation using a Clevenger apparatus, on the growth of pathogenic microorganisms (Pseudomonas sp., Staphylococcus aureus ATCC 14458, Escherichia coli ATCC 11229, and Listeria monocytogenes ATCC 7644) and probiotic strains (Lactobacillus acidophilus, L. bulgaricus, and Saccharomyces cerevisiae JP14). Dried P. guajava leaves were distilled with 1 L of water for 2 hours, and the resulting hydrolates were tested at concentrations of 25%, 50%, and 75%. Antimicrobial activity was assessed based on the specific growth rate (µ) and generation time (tg). The results showed that increasing hydrolate concentration significantly reduced the growth rate of pathogenic microorganisms, prolonging generation time and possibly the lag phase. For Pseudomonas sp., H1 exhibited µ = 0.2128 (tg = 3.26 h) at 25%, decreasing to µ = 0.1800 (tg = 3.85 h) at 75%, demonstrating a concentration-dependent inhibitory effect. Hydrolate H2 was the most effective against Pseudomonas sp., particularly at 75% concentration. In S. aureus ATCC 14458 and L. monocytogenes ATCC 7644, higher concentrations (75%) also resulted in generation times exceeding 4 hours, reinforcing the dose-dependent nature of inhibition. For E. coli ATCC 11229, the response varied according to hydrolate type and concentration. H2 increased generation time by approximately 40% (3.43 → 4.81 h), while H3 exhibited a non-linear behavior, with a slight stimulatory effect at 50% and pronounced inhibition at 75%. This pattern suggests initial adaptive adjustments by the cells (prolonged lag phase) and confirms the dose-dependent antimicrobial action of the hydrolates. Among non-pathogenic microorganisms, sensitivity varied depending on the strain and hydrolate. L. acidophilus and L. bulgaricus displayed prolonged generation times (exceeding 30 h in some treatments), indicating greater susceptibility, whereas the isolate S. cerevisiae JP14 maintained more stable µ values at intermediate concentrations, suggesting higher tolerance. This behavior underscores the need to adjust dosages to achieve selective antimicrobial activity, that is, inhibiting pathogens without compromising beneficial strains. In summary, the hydrolates demonstrated promising and concentration-dependent antimicrobial potential, acting more strongly against pathogenic bacteria. However, the observed sensitivity of certain probiotic strains highlights the importance of optimizing application concentrations, particularly for use in food or symbiotic formulations.