Aflatoxin in Corn

AND SUMMARY Low incidence and levels of aflatoxin were identified in corn of all grades grown in the Midwest in 1964, 1965, and 1967. Later surveys indicate that corn grown in southern regions is subject to invasion by Aspergillus flavus and subsequent aflatoxin formation. This mycotoxin is formed either in the field or in storage. In the field, such factors as insect damage and weather conditions probably influence aflatoxin formation. In storage, temperatures must be above 25 C and moisture levels above 16% if toxin is to form. Aflatoxin formed in a hot spot in stored corn in the Midwest when temperatures rose -early in the summer and when the grain became wet because of leaks in the storage building. Analytical methods to detect and determine aflatoxin fall into three categories: presumptive tests indicating the presence of A. flavus and the possible occurrence of aflatoxin, rapid screening tests establishing the presence or absence of the toxin, and quantitative procedures determining toxin levels. Detoxification methods being studied include ammoniation and roasting. Ammoniated corn is being fed domestic animals to determine whether it has adverse effects a,nd whether toxic compounds are transmitted in animal tissues. The results of several surveys (1-3) have indicated a significant occurrence of aflatoxin in corn grown in various regions of the country. Actions by the Food and Drug Administration (4,5) in recalling corn meal allegedly tainted by aflatoxin and seizing corn caused concern in the corn industry. Extensive programs to monitor corn for aflatoxin have been initiated by both industry and governmental agencies. Some of the first studies of aflatoxin naturally occurring in corn were made on 1964, 1965, and 1967 corn of all grades moving through commercial channels in the Midwest (6,7) (Table 1). The results of these studies did not appear to be alarming because of the low incidence (2.1-2.3%) and low levels (3-37 ppb total) of toxin detected, mostly samples of poorest grades. The ratio of the samples in the poorest grades assayed to those in the better grades assayed was higher than the ratio of these moving through the market. In 1965, analyses for aflatoxin B1 were performed on official grain inspection samples taken from 230 cars of corn purchased for delivery to six different wet milling plants (8). Only four of the 230 examined contained aflatoxin in levels of 3 to 5 ppb (Table 1). In the same study, lots of corn in three processing plants were sampled daily for a year and composited into 142 weekly samples. Aflatoxin B1 was detected in six of the weekly samples at levels of 3 to 5 ppb. Persons in the corn wet-milling industry concluded that corn arriving at major markets is largely free of aflatoxin at the time sampled. Aflatoxin B1 was found in spot samples from eight of 500 carloads of corn visually inspected by the corn wet millers. All.of the eight carloads had visible mold damage, and two had already been rejected on this basis. The potential for aflatoxin contamination does exist in improperly handled corn. A survey for aflatoxin in export corn in all grades except U.S. No. 1 collected from ten ports was made in 1968 and 1969 (9) (Table 1). The incidence was 2.7% and levels of 216A aflatoxin B1 were from <6 to 25 ppb. Positive samples occurred in the better grades, but relatively few of the total samples assayed were in the poorest grades. In a study of 1971 and 1972 preharvest corn in Indiana, no aflatoxin was detected in the 525 samples collected (10). However, eight of 163 combine-harvested corn samples obtained in 1972 from yield plots near Evansville, Indiana, were aflatoxin-positive. Higher incidences and levels of aflatoxin have been observed in corn grown in the South. In 1969 and 1970, 60 corn samples from Alabama, North Carolina, South Carolina, Tennessee, and Virginia were analyzed for aflatoxin (1). There were 21 positive samples (Table I) and levels of the toxin were higher than those observed in previous surveys (6-9). Aflatoxin was detected in 31% of 1283 truckloads of white corn delivered from 77 loans in seven counties in southeastern Missouri (2) (Table 1). Usually the corn from one loan came from one farm. All of the white corn was from the 1971 crop year and had been stored on the farm for 1 yr. Only 13% of the samples contained more than 20 ppb, the Food and Drug Administration (FDA) guideline. All of the truckloads of corn from one farm contained more than 100 ppb total aflatoxin. However, sipce aflatoxin was not detected in any corn from 20 of the loans, it is possible to grow, harvest, and store corn without toxin formation in an area where conditions are favorable for its formation. In a survey of 1973 corn freshly harvested in northeastern South Carolina, 51 % of 297 samples examined contained detectable aflatoxin (Table I) and 32% contained aflatoxin B1 above 20 ppb (3). The Grain Division, Agricultural Marketing Service, USDA, tested commercial lots of marketed corn for aflatoxin in 1972, 1973, and 1974 (11). In 1972, all samples (7913) submitted for grading to 18 field offices were inspected for the bright greenish-yellow (BGY) fluorescence associated with Aspergillus flavus and possibly aflatoxin to determine which samples to assay for aflatoxin. Samples were tested by the CB method approved in Official First Action by the Association of Official Analytical Chemists and the American Association of Cereal Chemists (12,13) and by a screening method using a Florisil minicolumn (14). Approximately 1.1 % of the samples had detectable aflatoxin by the CB method, and 1.5% were positive by the screening method (minicolumn). Only 0.3% of the corn samples had levels of aflatoxin higher than 15 ppb. In 1973, the survey was limited to 2866 systematically selected from 17,245 samples submitted to 16 field offices. The samples were inspected for BGY, and BGY-positive samples were tested using the Florisil minicolumn technique. The same approach was used in 1974. Larger numbers of samples were collected from field offices where the incidence of aflatoxin is expected to be high. Taking into account the disproportionate sampling rates, the estimated incidence of aflatoxin in corn in the early part of 1973 was 7.1 %. During the same period in 1974, the estimated incidence was 11 %. The screening methods used did not differentiate among the different aflatoxins but measured the total aflatoxin contamination. At present, the Grain Division is screening for aflatoxin in three inspection offices: Omaha, NE; St. Louis, -MO; and Norfolk, VA. Samples of 1972 crop corn were collected by FDA (15) in the spring of 1973 in areas known to have problems with Fusarium contamination and damage. Samples were obtained from terminal elevators and stocks on hand at food processing plants. The corn was analyzed for aflatoxin as J. AM. OIL CHEMISTS' SOC•• March 1977 (VOL. 54) -oi " " .. u " ,:: " .. .. ::I ~r55 "0 .. ~ u ." II ::I