Cereals including rice are carriers of a high content of microbes of natural origin. This problem is augmented by the deficiencies of proper handling during harvesting and storage. Contamination of food grains by some fungi such as Aspergillus, Pencillium, and Fusarium species is actually known to occur very widely. During their growth, those fungi produce a group of toxic metabolites, collectively known mycotoxin. Consumption of such contami nated foodstuffs has been shown to be hazardous to a variety of animals and human. Various fungi such as Aspergillius flavus, Aspergillus parasiticus also have been found and reported in Korea. This paper presents data from a survey on the contamination of fungi in cereals and their problems in Korea.
As Japan suffered damage caused by cold weather, rice production dropped to 26% below normal last year and Japan decided to import rice from foreign countries such as Thailand, the USA, China and Australia. Three inspection stages have been carried out to assure the safety of the rice before permission to import into Japan is given: 1) inspection of the rice by the Overseas Merchandise Inspection Co. Ltd. (OMIC) located in the exporting country for various kinds of pesticides, toxic heavy metals and aflatoxins, 2) rice samples in the same lot are sent to Japan by air for further analyses of the same contaminants mentioned above by the Japan Grain Inspection Association, 3) if the inspection results show no violation of Japan Food Sanitation Acts, the rice is shipped to Japan, and the third inspection is conducted by the Quarantine Office according to the Food Sanitation Acts, and by the Plant Quarantine Station and the Food Agency. The rice is then permitted to be imported if no problems are detected. Test items in Quarantine Centers are for 61 pesticides established by Japan Food Sanitation Acts and other pesticides suspected to be used in the exported countries, and aflatoxins. As of July, no samples contained more than the maximum residue limits of these chemicals.
Fifty-eight strains of Gibberella fujikuroi were isolated from Bakanae-diseased seedlings of rice, and examined both for the susceptibility to benomyl fungicide and for the producibility of f umonisin mycotoxin. Among these strains, 46 strains (79%) were resistant to benomyl (MIC, >100 μg/g), and 57 strains showed the pathogenicity to rice seedlings, and all strains produced gibberellin Aa in liquid culture. Fumonisin was produced by 8 strains (14%): 23∼860 μg/g (mean, 380 μg/g) and B2 1∼43 μg/g (mean, 23 μg/g) in corn culture. The fumonisin producibility of these strains was also found in polished-rice culture, but the f umonisin concentrations in rice culture were lower than those in corn culture. Six strains of these producers were resistant to the fungicide. The incidence of fumonisin producers in G. fujikuroi associated with Bakanae disease and their producibilities of the mycotoxin were apparently low as compared with those of Fusarium moniliforme and F. proliferatum isolated from other substrates such as corn.
A field study was conducted in crop fields with wheat-rice rotation in Kagawa in order to examine the relationship between the incidence of trichothecene-producing Gibberella zeae and Fusarium graminearum in the field and the occurrence of trichothecenes such as nivalenol (NIV) and deoxynivalenol (DON) in wheat. Ninety % (28/31) of G, zeae isolates from perithecia on debris of rice stubbles in wheat fields in Kagawa were mycotoxigenic, and, of these toxic isolates, 27 (96.4%) and 1 (3.6%) were NIV- and DON-producers, respectively. All of 54 isolates of dispersal G. zeae ascospores collected in a field in Miki, Kagawa, showed the toxin producibility: 46 (85.2%) and 8 (14.8%) isolates for NIV- and DON-producers, respectively. Furthermore, all of 20 isolates of F. graminearum from wheat grains harvested in the Miki-field were also toxigenic: 13 (65%) and 7 (35%) isolates for NIV- and DON-producers, respectively. The ratio of mean levels of NIV to DON in two wheat samples was 59.7% to 40.3%. Thus, the occurrence of the toxins in wheat was positively correlated to the incidence of the toxigenic fungi in the field.
A survey for occurrences of Fusarium mycotoxins in Korean and imported cereals was conducted. Thirty eight samples of cereals harvested in 1990 from 9 provinces in Korea, thirty six samples of cereals imported in 1989 and 1990, eleven samples of cereals donated from Iran were analyzed for deoxynivalenol (DON), nivalenol (NIV), T-2 toxin and zearalenone (ZEN) using gas chromatography, high performance liquid chromatography and gas chromatography/mass spectrometry. Among the 85 cereal samples, 17 samples were found to be positive for DON, NIV, T-2 toxin and ZEN in the range of 106-368 ng/g, 105-395 ng/g and 7-697 ng/g, respectively. The contaminated mycotoxins were DON in barley (Korea and Iran), rice (India), corn (Korea and China), wheat (Canada, France and India) and oats (Iran), NIV in rice (Japan), wheat (Iran and Canada) and oats (U.S.A.), T-2 toxin in barley (Canada) and ZEN in barley (Korea and Canada), corn (U.S.A. and China), oats (Canada) and grain sorghum (Korea and U.S.A.).
A method for qualitative and quantitative determination of Fusariuna mycotoxins by gas chromatography/mass spectrometry (GC/MS) was improved. Eight typical Fusariuin mycotoxins, deoxynivalenol (DON), 3-acetyldeoxynivalenol (3ADN), fusarenon-X (FX), diacetoxyscirpenol (DAS), 15-monoacetylscirpenol (15MAS), T-2 toxin (T-2), scirpentriol (SCT), and zearalenone (ZEA) were subjected to GC/MS without chemical derivatization by means of on-column injection technique. Chromatographic separation of the toxins was achieved with Rtx-200, 30m×0.25mm i.d. capillary column with a 0.25 mm film thickness as a single peak. The fatty acids in the extract that interfere with measurement of the toxins on gas chromatogram were removed by zinc acetate treatment forming insoluble precipitate as metal soap. Additional clean-up was accomplished using Bond Elut Florisil cartridge. The quantitative detection limit ranged from 0.1 to 0.5 ppm. The average recoveries of 93.1% for DON, 3ADN, 15MAS, DAS, T-2 and ZEA, and 46.0% for FX and SCT fortified to barley at level of 1 ppm were obtained.
Soil samples from the tea fields located from the central to southern parts of Japan were surveyed for Aspergillus fungi. Sixty three soil samples from 13 prefectures were examined using Aspergillus Flavus/Parasiticus Agar and Dichloran Rose-Bengal Chloramphenicol media that are selective for Aspergillus fungi. In 11 soil samples from 7 prefectures, Shizuoka, Mie, Siga, Kochi, Fukuoka, Nagasaki, and Miyazaki, 27 strains of A. Favus group fungi were isolat-ed. Among these, 4 isolates from 3 prefectures, Mie, Kochi and Miyazaki, produced aflatoxins. One of these isolates from Miyazaki prefecture produced more than 10 ppm of aflatoxin B1 in a liquid medium. Twenty one isolates from 6 prefectures produced cyclopiazonic acid (CPA). Several of these isolates produced more than 5 ppm of CPA in a liquid medium.
The production of zearalenone and its reduced compound, zearalenol, by Fusariurn graminearurn growing in the sterilized barley was analyzed. Zearalenone and zearalenol were determined by high performance liquid chromatography. The ratio of zearalenone and zearalenol content during the period (1 to 10 days) of incubation varied among the tested strains and the production of zearalenone was influenced by the concentration of zearalenol in some strains.