Few years ago melamine detected in dairy products caused panic to the public. Recently a milk product from a milk manufacturing plant in China was again detected with a toxic substance - sodium thiocyanate (15.2 mg/kg) which exceeded the food safety action level adopted by the Mainland government（≤10 mg/kg）1. This incident again causes people to worry about the safety of dairy products.
Sodium thiocyanate is a white powder or crystal which can inhibit the growth of microorganisms. In the past where cold chain logistics were not good, sodium thiocyanate was added to milk as a low-cost preservative. This can prevent food from deterioration and extend their shelf life.
Why Sodium Thiocyanate is Banned?
Sodium thiocyanate is also a toxic substance to human health, which can lead to acute poisoning. For example, excessive intake of sodium thiocyanate will lower the absorption and utilization of iodine by human, and result in thyroid disorders, particularly affecting neural development and IQ of fetus and baby.
In this connection, Mainland government banned the use of sodium thiocyanate as a preservative in milk and milk products since 2008. In Hong Kong, sodium thiocyanate is also not an approved food preservative.
On the other hand, in case cold temperature control cannot be achieved during food transporation and storage, Codex Alimentarius Commission (Codex) shall allow the use of sodium thiocyanate in raw milk, provided that the dosage is 14 mg/kg. At the same time, Codex emphasizes that sodium thiocyanate should not be added to milk products for international trade purpose.
Indeed cold chain logistics in China nowadays is already well developed; sodium thiocyanate is no longer needed for preserving dairy products.
Why the Tolerable Level of Sodium Thiocyanate is Not Zero?
Although sodium thiocyanate is already classified as an illegal additive, food without added chemicals can still be detected with sodium thiocyanate. This is because sodium thiocyanate can also occur naturally in a wide range of food. Therefore, it is not reasonable and infeasible to set the tolerable level of sodium thiocyanate in milk as zero.
A literature2 stated that raw milk might contain naturally occurring sodium thiocyanate at a level of 2 to 15 mg/kg. However, a widely accepted conclusion regarding the natural level of sodium thiocyanate in milk & milk products is yet to make.
However, in order to strengthen the control on illegal additives and lower the food safety risk, China Food and Drug Administration has established an action level for detection of sodium thiocyanate present in liquid milk products（≤10 mg/kg）. Products exceeding 10 mg/kg will be considered as “fail”.
Food Traders Should Test Before Buy
Nowadays some food manufacturers / producers still use illegal additives (like sodium thiocyanate) to make profits even though they know this violates the law. In this connection, food importers, food distributors and food retailers need to protect their own reputations by testing food they tend to buy, rather than just relying on the government to safeguard the food safety. They can either do the testing themselves or submit the food samples to accredited and independent testing laboratories for food safety assurance. Common analytical methods for sodium thiocyanate include ion chromatography, gas chromatography-mass spectrometry (GC-MS), etc.
Food Traders Should Audit their Suppliers
Apart from testing incoming food, another important food safety tool is regular food supplier audit. If the raw materials (e.g. milk) are garbage, then the end-product made of the problematic raw materials is still garbage. That’s why a food trader has to conduct an on-site audit of food production environment, production processes, test results, product traceability, etc. Supplier audit will enable food traders to choose a “qualified” food supplier (e.g. a milk product manufacturer who does not use illegal additives at all).