A slew of scandals involving the fraudulent substitution of beef and mutton with cheaper cuts of duck meat has put the spotlight on the scam, with fears the illegal practice could be happening on a wider scale across the food industry.

Authorities in Hohhot, capital of the Inner Mongolia autonomous region, recently levied a collective fine of 270,000 yuan ($36,700) on five food services contractors operating in a local college cafeteria, after analysis of food samples showed they had been passing off much cheaper duck meat as beef and mutton in their dishes since March.

A further 16,374 yuan was also confiscated as "illegal revenue", according to a penalty notice issued by Hohhot's Yuquan district market regulator.

"The practice constitutes food service fraud according to the Law on Consumer Protection," said the Sept 4 document, which was addressed to the Inner Mongolia University, a prestigious institution in the region.

The market regulator received reports in June that four food stalls in one of the university's cafeterias, and a Muslim canteen were engaged in the fraudulent activities.

The market watchdog collected samples from the food services contractors involved and confirmed the complaints, according to China National Radio.

University authorities severed ties with the contractors in early July before the official investigation concluded, it reported.

On Sunday, the college issued an apology to its faculty members and students, saying more oversight was needed. It also pledged to increase day-to-day monitoring of food quality and improve cafeteria services.

In an interview with CNR, an unnamed university management official said: "The mistakes were made by several contract food stalls, but the blame was on the college."

The official acknowledged that campus authorities had failed to properly supervise the contractors, and said they have taken over the operation of the food stalls from the contractors.

The meat scandal in one of China's major pastoral areas has drawn widespread public anger, because beef and mutton are supposed to be cheaper and more readily available in the region than in other parts of the country.

The campus scam is also the latest in a string of exposes involving food services fraudulently passing duck meat off as beef and mutton, which are roughly three times the price.

Banu, a hotpot chain, on Thursday said that it will refund a total of more than 8.3 million yuan to customers who ordered mutton rolls at one of its restaurants in Beijing's Chaoyang district since mid-January.

The costly compensation came after an internet influencer alleged recently that the mutton rolls sold in the Chaoyang restaurant contained duck meat, and urged the chain to conduct a third-party product analysis and publish the results. The chain complied and found the rolls involved were a mixture of mutton and duck meat.

"Banu is willing to spare no expense to compensate customers," said a statement on the hotpot chain's WeChat account, which has been viewed more than 100,000 times and received more than 1,000 likes.

In Hebei province, a restaurant that is part of the Zhangliang Spicy Hotpot chain was exposed by bloggers last month for selling "mutton" rolls, which instead contained pork and duck meat.

The chain said the restaurant involved did not know the raw materials it purchased were substandard, and pledged to strengthen the management of its supply chain.

Zhong Kai, an expert with the Chinese Preventive Medicine Association, told a news website owned by China Central Television that duck meat resembles mutton in looks but is cheaper. However, duck meat carries no health risks and therefore is not banned.

A search on an e-marketplace showed that duck meat rolls processed with sheep fat sell for around 15 yuan a kilogram, compared with pure mutton rolls costing up to 120 yuan a kilo.