Mycoflora and ochratoxin A producing strains of Aspergillus in Algerian wheat.
Wheat is a basic staple food for very large segments of the population of Algeria. The aim of this study is to analyse ochratoxin A (OTA)-producing mould and OTA-contaminated wheat. To evaluate the mycoflora and the potential for OTA production by Aspergillus strains, a total of 85 samples of wheat destined for human consumption were collected from two regions in Algeria (Tizi Ouzou and Setif) during the following phases: preharvest, storage in silos, and after processing. The mean value counts of fungi ranged from 275 to 1277 CFU g-1. The dominant genus was Aspergillus, predominantly A. flavus, A. niger and A. versicolor. The other isolated species were A. ochraceus, A. alliaceus, A. carbonarius, A. terreus, A. fumigatus, A. candidus and Aspergillus spp. The occurrence and the levels of the genus Penicillium, Fusarium, Alternaria and Mucor were substantially lower than those of Aspergillus. The storage in silos shows high levels of Aspergillus (66 to 84%), especially A. flavus, but A. niger and other fungi were isolated at relatively low percentages. Equal distribution of the fungal contamination into the bran, flour and semolina fractions was observed from Flour Mill and Semolina Mill. The genus Aspergillus remained present at high levels at several phases of the production process. In addition, the ability to produce OTA by 135 isolates belonging to eleven species of Aspergillus and 23 isolates of Penicillium spp. was analyzed using fluorescent detection-based HPLC. Thus, it was found that 51 isolates (32.3%) were ochratoxigenic. All isolated strains of A. ochraceus (12) and A. alliaceus (6) produced OTA at concentrations ranging from 0.23 to 11.50 µg g-1. Most of the A. carbonarius strains (80%) were OTA producers (0.01 to 9.35 µg g-1), whereas A. terreus (50%), A. niger (28%), A. fumigatus (40%), A. versicolor (18%) and Penicillium spp. (21.7%) were low level producers (0.01 to 0.07 µg g-1). The concentration of OTA was determined in 30 samples of wheat. OTA was detected in 12 (40%) of the samples at levels ranging from 0.21 to 41.55 µg kg-1.