The Shanghai Bureau of Quality and Technical Supervision said it was inspecting 116 companies producing snacks in Shanghai following on from an incident whereby a local firm produced tainted buns in addition to relabeling outdated food, reports the Shanghai Daily.
Five employees of the bun manufacturer, Shanghai Shenglu Food Co, have been detained as part of the investigation, said the city officials.
An investigation into the popular Chinese food was launched after a television programme exposed production problems, according to the local media outlet.
The Shanghai food safety agency said it inspected 19 batches of the company's products and found four contained a lemon yellow food coloring not allowed in the product and two had excess amounts of artificial sweetener.
The company's food producing certificate has been cancelled, said the bureau, adding that more than 32,220 steamed buns had been removed from supermarket shelves and sealed as part of the inquiry.
The maximum content of sweetener in Chinese-style cakes and buns is 0.65 grams per kilogram, but the buns contained up to 1.1 grams per kg officials said.
Flour bleach ban
Last month saw the Chinese authorities outlawing production of two food additives commonly used to bleach flour in response to consumer demand for natural foods and reduced reliance on chemical modifiers.
Flour is mostly used to make noodles, dumplings and steamed buns in China, especially in the north.
The Chinese ministry of health, in a statement on its website, said benzoyl peroxide (BPO) and calcium peroxide are no longer required for incorporation into flour given the fact the country's processing techniques and wheat planting had improved, reports official news agency Xinhua.
Manufacturers are no longer allowed to produce the two food agents or use them in flour production beginning next month. However, flour and related products containing the additives are allowed to be sold until the shelf life of such products expires.
The move follows a public consultation on the use of such additives in foods, with calls for BPO to be outlawed in the wake of the 2008 melamine contaminated milk incidents.
In April last year, Xinhua reported that pulverised lime was being added to bleaching agents used in Chinese flour in a bid to cut production costs and boost profits.
Tainted milk deaths
Meanwhile, last week saw another tainted milk scandal hit the Chinese dairy industry when three children died as a result of drinking nitrite contaminated milk and 35 others were taken to hospital.
The state news agency Xinhua reported that, as part of the investigation into the incident, police have arrested a couple, who co-rent land with a dairy farmer in Mafang village near Pingliang City.
The Chinese government has sought to clean up the dairy industry with new food safety laws and tougher enforcement.
Most recently Chinese authorities pulled the licenses of more than half the dairies operating in the country. Only 643 out of the 1,176 dairies in the country were granted production licenses, forcing the rest into temporary closure.