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. / Graduation date: 1974
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/26954 |
| Date | 20 July 1973 |
| Creators | Stutz, Howard Kent |
| Contributors | Krumperman, Paul H. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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