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Abstract
Microscale cultures of 5 ml Yeast Extract Sucrose (YES) broth in 4 dram vials were used to study effects of sorbate and propionate on growth and aflatoxin production by heat (55 C, 15 min) and gamma-irradiation (50 Krad) injured spores of Aspergillus parasiticus. Rapid aflatoxin quantification was done by thin layer chromatography (TLC) using direct spotting of YES broth on TLC plates. Injury to spores did not result in increased aflatoxin production. However, radiation injury caused accelerated aflatoxin production in the early stages of growth. Injured spores were more susceptible to inhibitors than uninjured controls, and aflatoxin production by injured spores was greatly reduced. However, sorbate (0.05%) was found to increase aflatoxin production significantly in diluted non-injured spores. At the same level of growth inhibition, propionate was more inhibitory to aflatoxin production than sorbate. Effects of sorbate and radiation injury on growth and aflatoxin production were studied in food systems (cooked rice and corn meal), findings were in agreement with those observed in YES broth system. Characteristics of foods had a great effect on aflatoxin levels produced. Increased aflatoxin production was found in irradiated and non-irradiated but diluted spores grown in cooked corn meal only. The addition of sorbate (0.5 and 1.0%) reduced total aflatoxin production but accelerated the onset of aflatoxin production by irradiated spores and non-irradiated diluted spores. Sorbate was more inhibitory to growth and total aflatoxin production than propionate applied at the same concentration. Aspergillus spores had increased sensitivity to sorbate in the later stages of spore germination, while spores germinating in a medium originally containing a subfungistatic level of sorbate were able to overcome sorbate inhibition. Protein and RNA synthesis patterns of germinating spores were changed by exposing spores at different germinating stages to sorbate.
