BEIJING - A research project is underway to identify cooking oil made from leftovers from restaurants, according to a statement from the Ministry of Health (MOH) Sunday.

The MOH, the State Food and Drug Administration and other related authorities have jointly made a plan for the research, said the statement.

The authorities have also set up an expert panel formed by experts specialized in edible oil processing, food safety and chemical analysis in the research.

According to the statement, it is technically difficulty to tell the illegally reprocessed oil from ordinary oil with regular testing methods.

Chinese police have arrested 32 suspects who allegedly produced "gutter oil" and sold them to restaurants in the country's latest major crackdown on the illegal oil.

More than 100 tonnes of the oil was seized after police busted the criminal network spanning 14 provinces, the Ministry of Public Security reported earlier this week.