Effect of temperature cycling on the production of aflatoxin by Aspergillus flavus Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/sq87bw60k

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  • The effect of cycling temperatures on production of aflatoxin by Aspergillus flavus (V3734-10) when grown upon various substrates was studied. The parameters of temperature and time were selected to simulate environmental conditions in Oregon during harvest of filberts and walnuts. The heat input required for aflatoxin synthesis in terms of degree hours per day were calculated and may be used as an index to predict potential danger of aflatoxin contamination. Conditions which generated less than 208 hours per day did not receive sufficient heat to induce growth and metabolism. When heat input ranged between 208 and 270 hours per day, growth and metabolism occurred with the development of a yellow pigment. There was not sufficient heat input, however, to induce the idiophase, sporulation and subsequent aflatoxin synthesis. Above 270 hours per day the culture entered the idiophase, sporulation occurred and aflatoxin was produced. The heat requirements for aflatoxin production was compared to the degree hours produced in the orchards by prevailing weather conditions at the time of harvest. The nuts are most susceptible to contamination and fungal growth during harvest when the nuts are damp and on the ground. During October and November, heat input is too low for aflatoxin production. From mid September to October heat input may be sufficient for aflatoxin production but at this time most walnuts and filberts are still tree borne and moisture in the environment is likely to be a limiting factor. A. flavus was found to be a poor competitor when grown with the natural fimgal flora isolated from moldy nut meats. On rice and nutmeat substrates, A. flavus was completely overgrown by members of the natural flora; even when A. flavus spores were present in superior numbers. Aflatoxin was not detected in the substrates of these cultures.
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  • description.provenance : Approved for entry into archive by Patricia Black(patricia.black@oregonstate.edu) on 2012-01-25T16:10:17Z (GMT) No. of bitstreams: 1 STUTZHOWARD1974.pdf: 548082 bytes, checksum: 09c10f30e3aaf3f2dee8d1d19a77dfcc (MD5)
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  • description.provenance : Made available in DSpace on 2012-01-25T16:10:17Z (GMT). No. of bitstreams: 1 STUTZHOWARD1974.pdf: 548082 bytes, checksum: 09c10f30e3aaf3f2dee8d1d19a77dfcc (MD5) Previous issue date: 1973-07-20

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