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Exploring the antimicrobial activity of fermented and non-fermented cocoa bean shell extracts through metabolomics
Yie Kie Chong1, Wei Khang Gan1, Joash Ban Lee Tan1
1School of Science, Monash University Malaysia Campus, Bandar Sunway, Malaysia.
Background:
Cocoa bean shell (CBS) extracts have emerged as a promising source of antimicrobial compounds. However, the bioactive compounds responsible for their antimicrobial activity have not been studied sufficiently. This study analyzed the antimicrobial properties of 12 extracts from fermented and non-fermented CBS, employing solvent and steam distillation extraction techniques to maximize bioactive diversity. The extracts were assessed against selected bacteria and fungi, including the 'ESKAPE' pathogens.
Results:
The CBS solvent and steam distillation extracts (except for ethyl acetate-fermented CBS) were found to exhibit antimicrobial activity against Streptococcus mutans with minimum inhibitory concentrations (MICs) as low as 0.0625 mg mL-1, whereas both fermented and non-fermented steam distillation CBS extracts were found to be active against Candida albicans with MICs at 1 mg mL-1. Overall, steam distillation extracts possessed enhanced antimicrobial activity in comparison with solvent extracts of CBS. Fermented CBS extracts were found to possess better antimicrobial activity than non-fermented CBS extracts. Metabolomics analysis identified theobromine (TB) and tetramethylpyrazine (TMP) as molecules that contributed to antimicrobial activity against S. mutans. Results showed that caffeine (CAF), TB and TMP were active against S. mutans and Acinetobacter baumannii, whereas CAF and TB were active against C. albicans. Significant synergistic effects of CAF, TB, and TMP with ciprofloxacin (CIP) were observed against Klebsiella aerogenes.
Conclusion:
These findings highlight the significant potential of bioactive compounds present in CBS for use in the development of sustainable antimicrobial agents. These naturally occurring compounds, including CAF, TB, and TMP, exhibited notable antimicrobial properties, which could also be harnessed to enhance the activity of commonly used antibiotics such as ciprofloxacin. Future studies could focus on determining the mode of action of these bioactive molecules. © 2025 The Author(s). Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.
