Masters Theses

Date of Award

12-1983

Degree Type

Thesis

Degree Name

Master of Science

Major

Food Science and Technology

Major Professor

F. A. Draughon

Committee Members

P. M. Davidson, H. O. Jaynes

Abstract

Mycotoxin contamination of grains can occur as a result of invasion by field fungi or by growth of storage fungi in improperly stored crops. Environmental factors and competing mycoflora can affect fungal growth and mycotoxin production. Since mycotoxins pose a potential health hazard to both man and animals, this study was conducted to evaluate combinations of temperature, initial moisture content (MC), and level of inoculum during storage of corn to determine optimal and limiting conditions for aflatoxin and ochratoxin production during fungal competition and growth in pure culture. Two fungi were used in this study, Aspergillus parasiticus NRRL 3145 and A. sulphureus NRRL 4077. Fungal spores were added to sterilized corn at levels of 10¹, 10³, 10⁵, and 10⁷ per 50g corn at 16%, 20%, 24%, and 28% MC. Samples were incubated at 20, 24, 28, and 32C for 3 weeks. Aflatoxins and ochratoxin A were then extracted from corn samples and analyzed by HPLC and TLC. More toxin was produced during fungal competition than when each fungus was grown alone. Maximum production of aflatoxin B₁, ochratoxin A, and total toxin was at a lower temperature (24C) in mixed culture than in pure culture. Maximum production of aflatoxin G₁ occurred at 24C in both pure and mixed culture. For aflatoxin B₁, G₁, ochratoxin A, and total toxin in mixed culture, 24C resulted in significantly more toxin production (P<0.05) than 20, 28, and 32C. In pure culture, 20C resulted in significantly less aflatoxin B₁, G₂, ochratoxin A, and total toxin production (P<0.05) than 24, 28, and 32C. Competition affected the temperature dependent relationship of aflatoxin B₁ and G₁. In both pure and mixed culture, 16% was the minimum MC for toxin production. For pure cultures, 16% MC resulted in significantly less aflatoxin B₁, aflatoxin G₁, ochratoxin A, and total toxin pro duction (P<0.05) than 20, 24, and 28% MC. Optimum conditions for toxin production were more limited during fungal competition. Inoculum was not a significant source of variation. Only for aflatoxin G₂ and ochratoxin A in pure culture did the 10¹ inoculum level result in significantly less toxin production (P<0.05) than the other three inoculum levels. No significant differences between inoculum levels were found in mixed culture. In summary, the presence of A. parasiticus enhanced ochratoxin A production by A. sulphureus and the presence of A. sulphureus enhanced aflatoxin production by A. parasiticus. Toxin production increased probably as a means of survival. Based on the results of this experiment, recommendations for corn storage to reduce or prevent toxin formation by A. parasiticus and A. sulphureus are: a moisture content < 16%; a temperature < 20%; and an inoculum level < 10¹ spores/50g since in some cases, 10 spores per 50 grams of corn resulted in toxin production.

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