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Isolation and Identification of Aspergillus spp. from Rotted Walnuts and Inhibition Mechanism of Aspergillus flavus via Cinnamon Essential Oil

Summary

Researchers collected rotted walnuts from storage in Shanxi, China and identified five types of Aspergillus fungi contaminating them, with Aspergillus flavus being the most common. They tested cinnamon essential oil as a natural antifungal treatment and found it effectively stopped fungal growth by damaging the fungi’s cell membranes and causing oxidative stress. This research suggests cinnamon essential oil could be used as a safe, natural alternative to chemical fungicides for preserving walnuts and other foods from fungal spoilage.

Background

Walnuts are prone to contamination by rotting fungi, particularly Aspergillus species, which produce mycotoxins posing significant health risks. Cinnamon essential oil (CEO) has demonstrated antimicrobial properties and offers a natural alternative to synthetic fungicides. However, limited research has explored CEO’s antifungal potential for walnut preservation or the microflora composition in walnuts across Chinese regions.

Objective

To investigate Aspergillus species contamination in moldy walnuts stored in Shanxi, China, identify the prevalent species using morphological and molecular analysis, evaluate the antimicrobial effects of CEO against dominant Aspergillus strains, and elucidate the antifungal mechanism through cell membrane integrity and oxidative stress analysis.

Results

Five Aspergillus species were identified with frequencies of: A. flavus (100%), A. fumigatus (93%), A. niger (78%), A. terreus (47%), and A. tubingensis (40%), with 358 total isolates recovered. The MIC of CEO against A. flavus was determined to be 0.78 g/L. CEO disrupted cell membrane permeability and integrity, increased malondialdehyde accumulation, and decreased superoxide dismutase activity, indicating oxidative stress-induced fungal inhibition.

Conclusion

The study successfully isolated and identified Aspergillus species in moldy walnuts, confirming A. flavus as the dominant pathogenic fungus. CEO demonstrated significant antifungal potential through mechanisms involving cell membrane disruption and lipid peroxidation, establishing it as a feasible green antimicrobial agent for walnut preservation. Further investigation is needed for large-scale practical applications across different food matrices.
  • Published in:Foods,
  • Study Type:Experimental Research,
  • Source: 10.3390/foods14030357
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