In order to obtain a breaf information albout extent of Contamination of foodstuffs by fungi especially by Aspergillus flavus which is known to produce aflatoxin, fungal and bacterial examination of flours and cereals on sale, such as buckwheat flour, wheat flour, roasted soybean flour, soybean and peanut, were carried out. Isolated fungi were identlfied and aflatoxin productivity of A. flavus found among them was studied.
Test material was suspended and homogenized in phosphate buffer saline and mix-cultured in potato dextrose agar containing chloramphenicol. After 7 days incubation at 27°C, number of the colonies of fungi and yeasts developed were counted. Fungi and yeasts were found from 77% of the materials tested over all; and 100, 90, 45.5, 78.9 and 73.3% from buckwheat flour, wheat flour, roasted seybean flour, soybean and peanut, respectively. Number of fungi and yeasts in average in each foodstuffs tested were as follows: 23, 000/g in buckwheat flour, 240/g in wheat flour, 90/g in roasted soybean flour, 130/g in soybean and 280/g in raw non-shelled peanut.
Bacterial counts made on plain agar were as follows: 170, 000/g in buckwheat flour, 860/g in wheat flour, 130/g in roasted soylbean flour, 400/g in soybean and 540/g in raw nonshelled peanut. Degree of fungal contamination did not correlate with that of bacterial contamination. Moisture contents of the test materials also showed no correlation with degree of fungal or bacterial contamination.
The most prevaling genus among isolates of fungi was Penicillum (43.8%) and next one was Aspergillus (24.0%). In addition to them, Cladosporium (6.3%), Rhizopus (3.1%), Cephalosporium (2.1%), Scopulariopsis (2.1%), Epicoccum (2.1%), Paecilomyces (2.1%), Mortierella (1.0%), Gonatobotrys (1.0%), Botrytis (1.0%), Monilia (1.0%) and Mucor (1.0%) were also isolated.
Among 23 strains of the isolates of Aspergillus, 10 were identified as A. flavus, of which 7 were isolated from buckwheat flour and the others were from wheat flour. Five strains of them were proved to elaborate aflatoxin B1 and/or B2 in vitro. Most of them produced the toxin only in a small amount, but one strain which was isolated from wheat flour produced toxin B1 in fairly large amount. It was estimated to be 23.2mg/kg of the mold rice medium by fluorodensitometric method. Toxicity of this toxin was tested by chicken embryo method. The value of LD50 was 0.125μg/Egg.
Aflatoxin itself was not detected directly in the material from which A. flavus was isolated.
