Microwave-assisted extraction of annatto: Effects of pH and time on antibacterial activity

Annatto seeds possess antimicrobial properties, but extraction methods may degrade bioactive compounds. This study investigated the impact of pH-adjusted microwave-assisted extraction using distilled water on antibacterial activity to obtain safe food-grade extracts. Extractions were performed at pH values of 4, 7, and 9 for extraction times of2, 4, and 6min, using a microwave power setting of 100W. The antimicrobial activity of the extracts was assessed against <i>Escherichia coli</i> and <i>Staphylococcus aureus</i> through inhibition zone analysis and viable bacterial cell count reduction. In parallel, the total phenolic content of each extract was quantified to examine the correlations between phenolic concentration and antibacterial activity. The findings revealed that extraction at pH 4 for 2min yielded the most pronounced antibacterial activity with a minimum inhibitory concentration (MIC) of 5%. The application of a 20% annatto extract resulted in the lowest viable cell counts of both <i>E.</i><i>coli</i> and <i>S.aureus</i>. Variations in pH and extraction time did not result in significant differences in total phenolic content, suggesting that antimicrobial efficacy may be influenced not only by phenolic concentration but also by the specific profile of active compounds.