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Modelling the Combined Effects of Oxalic Acid, Water Activity, and pH on the Growth and Mycotoxin Production of Aspergillus spp. in a Dried Fig System

Summary

Dried figs can become contaminated with harmful fungi that produce dangerous toxins during the drying process. Researchers used mathematical modeling to understand how water content, acidity, and oxalic acid treatment affect fungal growth and toxin production in figs. They found that reducing water content is the most effective way to prevent dangerous toxin buildup. These models help the fig industry identify and avoid conditions that promote contamination, ultimately making dried figs safer for consumers.

Background

Dried figs are susceptible to fungal contamination, particularly by Aspergillus welwitschiae and Aspergillus flavus, which produce ochratoxin A (OTA) and aflatoxins (AFs) respectively. Traditional sun-drying methods combined with high sugar content promote mycotoxin accumulation. Oxalic acid has been proposed as a potential preharvest elicitor to enhance fruit quality and disease resistance.

Objective

To model the combined effects of water activity (aw), pH, and oxalic acid (OA) on the growth and mycotoxin production of A. welwitschiae and A. flavus in a fig-based substrate. The study developed and validated semi-quantitative predictive models using response surface methodology with Box-Behnken design.

Results

Water activity was the most influential factor governing fungal behavior. The lowest aw (0.92) significantly delayed growth and completely inhibited OTA and AFB1 production. High aw (0.99) was prerequisite for significant mycotoxin accumulation. OA at tested concentrations did not prove potent as an independent inhibitor but its interactions with aw and pH significantly delayed fungal growth. Growth models showed high R² values (>96%), while mycotoxin models had more moderate R² values (51-86%).

Conclusion

The developed mathematical models serve as semi-quantitative tools for identifying high-risk conditions for mycotoxin contamination in dried figs rather than precise predictive instruments. Water activity emerged as the critical control point for managing both fungal growth and mycotoxin production. These models can inform preharvest and postharvest strategies to ensure fig safety in the Mediterranean region.
  • Published in:Foods,
  • Study Type:Experimental Study with Mathematical Modeling,
  • Source: PMID: 41300011, DOI: 10.3390/foods14223854
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