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Growth and aflatoxin production by Aspergillus parasiticus in a medium at different pH values and with or without
Abstract:
A glucose-yeast extract-salt medium containing 0, 5, 7.5, 10, 15 or 20 micrograms pimaricin/ml with an initial pH of 3.5 or 5.5 was inoculated with Aspergillus parasiticus WB 108 and incubated at 15 degrees or 28 degrees C. The pH, weight of mycelium and amount of aflatoxin produced were determined after 3, 7, and 10 days and after 14, 21, and 30 days when incubation was at 28 degrees or 15 degrees C, respectively. Increasing the concentration of pimaricin in the medium with an initial pH of 5.5 decreased the amounts of aflatoxin B1 and G1 produced after 3 days of incubation. When the initial pH of the medium was 3.5, no growth or toxin production occurred after 3 days of incubation in the medium containing 7.5 micrograms or more of pimaricin/ml. The presence of 20 micrograms of pimaricin/ml inhibited growth and toxin production after 7 days of incubation. When cultures were incubated at 15 degrees C, there was a lag phase which extended from 9 to 16 days, and the amounts of aflatoxin produced decreased with an increasing concentration of pimaricin. Pimaricin did not completely inhibit the growth and aflatoxin production by A. parasiticus. Pimaricin, in combination with a low pH, low temperature or 4% or 6% NaCl, initially caused slow mycelial growth and low toxin production, but the mold overcame the inhibitory effects and produced substantial amounts of mycelium and toxin.
Insights
Pimaricin and low pH/temperature initially inhibit Aspergillus parasiticus growth and aflatoxin production. However, the mold adapts, overcoming these conditions to produce significant toxins.
Area of Science:
- Food Microbiology
- Mycology
- Food Safety
Background:
- Aspergillus parasiticus is a significant producer of aflatoxins, which are toxic secondary metabolites harmful to human and animal health.
- Pimaricin, an antifungal agent, is explored for its potential to control fungal growth and mycotoxin production in food systems.
Purpose of the Study:
- To investigate the efficacy of pimaricin in inhibiting the growth and aflatoxin production of Aspergillus parasiticus under various conditions.
- To determine the combined effects of pimaricin with low pH, low temperature, and high salt concentrations on fungal development and toxin synthesis.
Main Methods:
- Aspergillus parasiticus WB 108 was cultured in glucose-yeast extract-salt medium with varying pimaricin concentrations (0-20 µg/ml).
- Experiments were conducted at initial pH levels of 3.5 and 5.5, and incubation temperatures of 15°C and 28°C.
- Mycelial weight, pH, and aflatoxin (B1 and G1) production were measured at different time points.
Main Results:
- Increasing pimaricin concentration reduced aflatoxin B1 and G1 production at pH 5.5.
- At pH 3.5, pimaricin concentrations of 7.5 µg/ml or higher completely inhibited growth and toxin production for 3 days; 20 µg/ml inhibited growth for 7 days.
- Incubation at 15°C resulted in a lag phase and decreased aflatoxin production with increasing pimaricin levels.
- Pimaricin, combined with low pH, low temperature, or NaCl, initially slowed growth and toxin production, but A. parasiticus eventually adapted and produced substantial amounts.
Conclusions:
- Pimaricin exhibits inhibitory effects on Aspergillus parasiticus growth and aflatoxin production, particularly when combined with low pH and temperature.
- However, pimaricin does not provide complete inhibition, as the fungus can overcome these inhibitory conditions over time.
- The study highlights the complex interactions between pimaricin, environmental factors, and fungal adaptation in controlling mycotoxin contamination.
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