Rice gruel sold mainly to children by many stalls in Ho Chi Minh City have been found using substances to keep it in "fresh" for days.
The city's Health Department has taken gruel samples for testing after all earlier samples collected by Tuoi Tre last week were found to contain banned chemicals.
The samples were taken last Tuesday from four shops on No Trang Long Street in Binh Thanh District. The ingredients listed on the package of the gruel do not mention any chemical.
Yet test results by the city Department of Science and Technology on Friday showed that all the samples contained sodium benzoate, which helps keep the gruel from being spoiled after three days in normal condition.
An employee of a chemical producer in Tan Binh District, who didn't want to be named, said he usually delivers chemicals to gruel shops in the city which make the gruel solid, fragrant and help keep it for three days without being spoiled.
Sodium benzoate is sold at VND50,000 (US$2.79) a kilogram and potassium sorbate at VND80,000 a kilo to keep the porridge look and smell good in normal temperature for longer time.
Xanthan Gum which is added to thicken the cereal also costs VND50,000 a kilo. The deliverer said the substance helps the shops save a "remarkable" amount of rice, shrimp, fish and meat.
He said each shop has their own "secret" method to mix the chemicals, usually 2 or 3 grams of chemicals for a kilo of gruel instead of 1 gram as instructed.
"Many gruel makers now do anything to make the children love eating porridge and their shops make earn more money."
Nguyen Minh Hung, chief inspector of HCMC Health Department, on Sunday told Tuoi Tre the department is going to release the results on more samples soon.
According to the department, the chemicals in question are banned from being added to gruel.
Dr Tran Van Ky from the Vietnam Association of Food Science and Technology said any chemical when used in food must have the approval of the Ministry of Health and the ministry's instructions about the quantity that is allowed to be used.
Ky, who takes care of food safety and hygiene for the association in the south, said the children's bodies are "very sensitive".
He said the chemicals will cause them to suffer digestion disorders, which after a long time can make them malnourished and hinder their development.
Nguyen Xuan Mai, former deputy head of the city Public Health Institute, said children taking the chemicals for a long time can suffer liver and kidney decline.