The interest on Aloe based natural products is fast growing during recent years, particularly regarding their nutraceutical and antimicrobial properties. However, the information available on this item is limited and discrepancies can be found in literature. In this work, the antimicrobial properties of Aloe barbadensis Miller and Aloe arborescens Miller dermal and inner gel leaf fractions on the growth of five microorganisms were studied. Generally, gram positive were more susceptible than gram negative microorganisms and a lower activity of all fractions against the beneficial Saccharomyces boulardii was observed. Albeit the antimicrobial effect of pure anthraquinones aloin and aloe emodin was confirmed, a higher activity was observed for the methanol/ethyl acetate extracts of epidermis and for the water extract of the gel. A synergistic effect of several compounds, additional to the anthraquinones considered, should therefore be supposed. Conclusively, the Aloe extracts had an antimicrobial activity which is strongly related to the plant species and leaf fraction considered and which is a function of the microorganism considered.
Key words: Anthraquinones, acemannan, diffusion disc method, tandem mass spectrometry.