Analytical uncertainty

Wang Bing, CEO of Beijing Techmate, which represents Japanese cosmetics firm

Shiseido's analysis wing in China, says that the methods currently being used to analyse

milk may not detect other contaminants that might also be present.

This is important because the impure industrial melamine added to milk often contains

a second compound, cyanuric acid. The two chemicals together can form insoluble

crystals, which can lead to the formation of kidney stones and ultimately kidney

failure. Melamine alone is less toxic - though prolonged exposure to the compound

could also cause health problems.

In addition, Wang says, different technical approaches - such as liquid chromatography

and gas chromatography - give quite different results when used to test for

melamine. But so far there have been no efforts from either the government or aca69

demia to work out why. 'More systematic approaches must be adopted in food contamination

tests,' Wang told Chemistry World.

Zhu Min of Perkin Elmer, who is responsible for melamine analysis at the firm, says

contamination testing should make better use of the latest technologies. 'Molecular

analysis technologies have been mature for 10 years, yet nitrogen levels remain the

sole measure used to determine milk's protein content,' Zhu says.

But the price tag attached to molecular analysis technology may be holding back its

wider use. Bo Tao, an LC/MS application engineer at Agilent, says even the cheapest

HPLC costs more than US$10,000 and the consumables needed to run the tests are

also expensive.

Meanwhile, China's Ministry of Science and Technology posted a note on its website

asking members of the public to submit testing methods able to identify the presence

of melamine in under 30 minutes. According to media reports, the ministry had received

more than 100 solutions by its 8 October deadline.

Research gap

The health implications of the melamine scandal remain uncertain. Though the compound

is known to cause kidney stones in babies, no adult incidence of the problem

has yet been reported - possibly because milk forms only a small part of the adult

diet.

On 7 October, the Chinese government stipulated that milk powder should contain no

more than 1mg of melamine per kilogram (approximately 1 part per million).

But the US Food and Drug Administration (FDA) said on 3 October that it is unable

to establish any 'safe' level of melamine and melamine-related compounds in infant

formula 'because of gaps in our scientific knowledge about the toxicity of melamine

and its analogues in infants'. In foods apart from infant formula, it declared that 2.5

parts per million melamine content did not raise concern. Meanwhile, the European

Food Safety Authority (EFSA) has stated that adults in Europe who consume chocolates

and biscuits containing milk powder contaminated with melamine would not exceed

the TDI (Tolerable Daily Intake) of 0.5mg/kg body weight.

Toxic economics

Meanwhile, the economics behind the melamine scandal have become clearer. Industrial

melamine costs about 12,000 yuan (US$1765) per tonne, much higher than the

price of milk - 1200-1800 yuan per tonne. But the practice of adding melamine to

milk is profitable because just one gram of melamine per kg of milk is enough to lift

the apparent protein content of milk from less than 27 grams of protein per kilogram

(the cheapest grade of milk in China) to greater than 31 grams per kilogram - the

most expensive grade.

So for 0.012 yuan (0.0018 US cents), producers can illegally boost the price of a litre

of milk from 1.2 yuan (17.6 US cents) to 1.8 yuan (26.5 US cents) per kilogram. If

the milk is diluted, the resulting profits can be even greater.

According to Chinese media reports, some milk collection stations may also have

heated milk and added citric acid to increase the amount of melamine they could dissolve

- the compound is only 'slightly soluble' (less than 0.9 grams in 100 grams) in

water at room temperature, but around 6 grams will dissolve into 100 grams of water

at 100°C, while the addition of citrate may keep the melamine from coming out of

solution when the milk cools down.

Date: 2015-12-17; view: 793