The Effects of pH, Temperature, and Oxygen Availability on the Production of Aflatoxin B1 by Aspergillus flavus Zt41 and Sterigmatocystin Production of Aspergillus creber 2663 Isolates

Abstract

Aflatoxin B1 (AFB1) is a highly carcinogenic substance primarily produced by Aspergillus flavus and Aspergillus parasiticus. Sterigmatocystin (ST), a precursor of aflatoxin, is mainly produced by Aspergillus nidulans and Aspergillus creber. Both mycotoxins have similar biosynthetic pathways and structural characteristics, yet ST is considered to be less carcinogenic than AFB1. The scope of this study is to investigate how environmental conditions such as pH, temperature, and oxygen levels influence the production of toxins by good AFB1 producer Aspergillus flavus Zt41 (isolated from corn in Hungary) and ST hyper-producer Aspergillus creber 2663 (isolated from a flour mill in Hungary) on rice substrate. Temperature played a significant role in mycotoxin production, particularly in the production of sterigmatocystin, which peaked at 26°C with 392 μg/g, which was 3–4 times higher than amounts measured for 18°C, 22°C, and 30°C in the presence of oxygen. Oxygen availability was crucial for both growth and toxin production, as anaerobic conditions significantly impeded these processes. The rice substrate effectively served as a buffer, significantly reducing the impact of pH changes caused by citrate buffers. This is the first detailed study on the effects of pH, temperature, and oxygen availability on ST production of the hyper-producer Aspergillus creber strain isolated from a flour mill in Hungary.