Time of Aspergillus flavus infection and aflatoxin formation in ripening of figs

Increased aflatoxin contamination of dried figs in a drought year

Dried figs (4917 samples) destined for export from Turkey to the European Union were collected between September and December during the very dry crop year of 2007 and tested for aflatoxins B(1), B(2), G(1) and G(2) by immunoaffinity column clean-up and reverse-phase high-performance liquid chromatography (RP-HPLC). While 32% of the samples contained detectable levels of total aflatoxins, 9.8% of them exceeded the European Union limits. Aflatoxin levels were in the range of 0.2-259.46 microg kg(-1) and 2.04-259.46 microg kg(-1) for all samples and samples that exceeded the limits, respectively. A substantial increase in the incidence of aflatoxins was observed in 2007 compared with previous years, most likely due to the drought stress, high temperatures and low relative humidity encountered during the period from January to September of that year. In 2007, the mean temperature was 1-2 degrees C higher, there was 300 mm less total rain, and the mean relative humidity was 10-15% lower than in 2002-06. The average concentration of individual aflatoxins present in the samples was quantified to determine whether the drought conditions promoted certain types of aflatoxins. Among the contaminated samples, aflatoxin B(1) occurred in 97% of the contaminated samples, followed by G(1) in 47%, B(2) in 24%, and G(2) in 6% of samples. Concentrations of individual aflatoxins exhibited great variability among the samples but were not significantly different from those reported in previous studies, which were conducted under conditions without drought and high temperatures.

Incidence of ochratoxin A in dried fruits and co-occurrence with aflatoxins in dried figs

Ninety eight dried figs, 53 sultanas and 20 dried apricots destined for export from Turkey to the European Union were tested for ochratoxin A (OTA) contamination utilizing immunoaffinity column clean-up and high-performance liquid chromatography (HPLC). While only 2 (4%) of the sultanas exceeded the 10 ng g(-1) maximum limit set by the EU, 28 (53%) of 53 sultana samples contained detectable levels of OTA, in the range of 0.51-58.04 ng g(-1). Eighteen of 98 (18%) dried figs contained detectable levels of OTA, in the range of 0.87-24.37 ng g(-1). Only one of the 20 dried apricots was contaminated, with 0.97 ng g(-1) OTA. Dried figs analyzed for OTA were also tested for aflatoxin contamination to determine the co-occurrence of both toxins. Seven samples were confirmed aflatoxin positive, in the range of 0.23-4.28 ng g(-1), and only 2 samples contained both toxins, with a maximum concentration of 24.37 ng g(-1)for OTA and 1.02 ng g(-1) for aflatoxin B(1). The average recovery and relative standard deviation (RSD) obtained from dried fruits spiked with OTA ranged from 80.5% to 91.5% and 0.99-5%, respectively. The average recovery and relative standard deviation (RSD) obtained from dried figs spiked with aflatoxin ranged from 88.78% to 93.53% and 2.54-7.25%, respectively.

Fungal Decay of First-Crop and Main-Crop Figs

Fig cultivars grown in California typically have two crops, although the first crop may be unimportant commercially. The first crop, also known as the breba crop, ripens in late spring and early summer, whereas the main or second crop ripens in late summer. For both cultivars studied, Conadria and Calimyrna, the first-crop figs typically are left in the orchard unharvested. First-crop figs had relatively high levels of fungal decay and tended to have more fungal decay than main-crop figs, especially Alternaria rot (caused by Alternaria alternata and Ulocladium atrum). At least 16 different Aspergillus spp. were found decaying first-crop figs. Fig smut, a serious disease caused by Aspergillus niger and related fungi, usually was present at approximately the same level in first-crop and main-crop figs. Aspergillus spp. known to produce the mycotoxins aflatoxin or ochratoxin were found decaying first-crop figs. Aflatoxin was detected in first-crop figs at low levels similar to those detected in the main-crop figs. Because the abundant spores produced on the first-crop figs can infect main-crop figs, the fungal decay of first-crop figs might result in higher levels of decay for main-crop figs.