LC-QTOF-MS Chemical Characterization, Cytotoxicity, and Antimicrobial Activity of Blue Geopropolis: An Emerging Type of Brazilian Propolis.

Background/

Objectives

This study characterized blue geopropolis from Melipona quadrifasciata quadrifasciata (southern Brazil) by comparing its chemical composition, cytotoxicity, antimicrobial activity, and coloration mechanisms directly against green and red Apis mellifera propolis under identical experimental conditions.

Methods

Ethanolic extracts of blue geopropolis, green, and red propolis were prepared, followed by hexane and chloroform fractionation. Chemical composition was analyzed by LC-qTOF-MS. Cytotoxicity was assessed in L929 fibroblasts, and antimicrobial activity was determined by minimum inhibitory concentration (MIC) assays against bacterial and fungal strains. The blue coloration was investigated using NaOH and FeCl3 treatments to evaluate the possible involvement of phenolic-iron complexes.

Results

Fifty-nine compounds were identified across the three samples, revealing several shared phenolic constituents as well as distinctive chemical features. None of the extracts showed activity against Gram-negative bacteria, including Escherichia coli and Pseudomonas aeruginosa (MIC > 1000 µg/mL). In contrast, activity was observed against Gram-positive bacteria, with MIC values ranging from 20.8 to 1000 µg/mL. Among the samples tested, blue geopropolis showed the strongest activity against Gram-positive bacteria. Blue geopropolis exhibited no significant activity against Candida albicans or Candida parapsilosis (MFC > 1000 µg/mL) but showed variable activity against Sporothrix spp. The colorimetric assay indicated that phenolic-iron complexation may contribute to the blue color.

Conclusions

Despite its distinct entomological origin, blue geopropolis shared chemical traits with green and red propolis while demonstrating superior Gram-positive antibacterial activity, a higher selectivity index, and potential antifungal applications against Sporothrix spp., highlighting its promise for biotechnological and pharmacological use.