Abiotic factors affect growth and aflatoxin B1 production by Aspergillus flavus strains on chilli powder and red chillies

Chillies and chilli-based products are important spices on a global basis. The production, processing, transport and storage phases of chillies are prone to infection by Aspergillus Section Flavi and contamination with aflatoxins (AFs), especially aflatoxin B1 (AFB1) for which legislative limits exist in many countries. We have examined the effect of the interacting abiotic factors of water availability (water activity, aw; 0.995-0.850 aw) and temperature (15-37 °C) on (a) lag phases prior to growth, (b) growth, (c) AFB1 production and (d) contour maps of optimum and boundary conditions for colonisation and toxin production by three Aspergillus flavus strains on a 10% chilli-based medium. Additional studies with whole red chillies + A. flavus conidial inoculum on AFB1 contamination during storage for 10-20 days at 30 °C were also carried out. In vitro, the lag phases before growth were delayed by lower temperatures (15, 20 °C) and aw levels (0.928-0.901 aw). There was no statistical difference in growth between the three strains. Optimal growth was at 37 °C and 0.982 aw with no growth at 0.85 aw. Optimal temperature × aw conditions for AFB1 production were at 30 °C and 0.982 aw with no statistical difference in production between strains. No AFB1 was produced at 15-20 °C at 0.901 and 0.928 aw levels, respectively. In situ studies with A. flavus inoculated whole red chillies at 0.90 and 0.95 aw found that this species became the major component of the total fungal populations at 30 °C after 10-20 days storage. AFB1 contamination was above the European legislative limits (5 μg/kg) for spices at 0.90 aw after 20 days storage and at 0.95 aw after 10 and 20 days. This suggests that storage conditions of ≥0.90 aw, especially at ≥25-30 °C represents a significant risk of contamination with AFB1 at levels where rejection might occur, even after only 10-20 days storage.