Study of gene expression and OTA production by Penicillium nordicum during a small-scale seasoning process of salami

Penicillium nordicum, an important and consistent producer of ochratoxin A (OTA), is a widely distributed contaminant of protein rich food with elevated NaCl. It is usually found on dry-cured meat products and is considered the main species responsible for their contamination by OTA. The aim of this work was to study the gene expression of a polyketide synthase (otapksPN) involved in P. nordicum OTA biosynthesis, and OTA production during a small-scale seasoning process. Fresh pork sausages were surface inoculated with P. nordicum and seasoned for 30 days. Gene expression and OTA production were monitored throughout the seasoning process after 4, 5, 6, 7, 10, 14, and 30 days. The expression of otapksPN gene was already detected after 4 days and increased significantly after 7 days of seasoning, reaching the maximum expression level after 10 days (1.69 × 104 copies/100 mg). Consistently with gene expression monitoring, OTA was detected from the 4th day and its content increased significantly from the 7th day, reaching the maximum level after 10 days. In the late stages of the seasoning process, OTA did not increase further and the number of gene copies was progressively reduced after 14 and 30 days.