Mechanism of puberulic acid contamination in red yeast rice tablets that caused a serious food poisoning outbreak in Japan

In Japan, serious food poisoning among individuals who took supplement tablets for lowering plasma cholesterol levels have been publicized since late March 2024. The tablets were prepared from red yeast rice (RYR), a product of Monascus pilosus. Puberulic acid (PA) was detected as an unexpected compound in tablets that caused food poisoning. We conducted an on-site investigation at the RYR production factory to determine the cause of PA contamination of the tablets. Fungi capable of producing PA were detected in wipe samples from the factory and were identified as Penicillium adametzioides. To understand the route through which P. adametzioides contaminated RYR and produced PA, coculture experiments with M. pilosus and P. adametzioides were performed. P. adametzioides grew on rice covered with M. pilosus and produced PA. These results suggest that PA-producing P. adametzioides inhabited the RYR production factory and accidently contaminated the culture of M. pilosus. Consequently, RYR tablets contaminated with PA were manufactured and caused the food poisoning outbreak.