How labs find out whether your food is safe
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Shop shelves in India have been emptied of one of the nation’s most popular easy-to-make meals—Maggi noodles—after samples were found to have more than the permissible level of lead and added monosodium glutamate. The testing is a mix of high-school chemistry and high-end instrumentation and requires a scrupulous adherence to standard procedures.
Food is tested for safety in laboratories accredited to the National Accreditation Board for Testing and Calibration Laboratories (NABL), an autonomous body under the department of science and technology. NABL lays down the standard procedures for detecting all kinds of adulterants and impurities for up to 17,000 kind of foods.
There are 12 referral labs and 72 state labs run by the government, and 65 private labs which are NABL-accredited and notified by the Food Safety and Standards Authority of India (FSSAI).
To be sure, government labs have been criticized for being ill-equipped and not filling vacant scientist positions by experts as well as government officials. In 2012, a former Central Food Laboratory director Satya Prakash wrote to the then health minister Ghulam Nabi Azad pointing out that six of the government’s referral labs were not equipped to carry out basic food tests on fruits and vegetables, carbonated drinks and milk and milk products.
Mint visited a private NABL-accredited food-testing laboratory in New Delhi to find out the science behind the bans.
Sample: These labs usually use 2-5g of a food sample to test for heavy metals.
Avoiding contamination: At all stages, extra care is taken to make sure the testing environment is free of contaminants. All flasks are rinsed and washed with normal water and detergents and then with distilled water. Extra care is also taken while preparing test solutions.
Working solutions: The samples are diluted according to FSSAI specifications to avoid any interference that could lead to incorrect results. Specified reagents or chemicals which are needed for the analysis by the instruments are kept prepared by labs.
• Cleaning up organic content: After getting rid of the moisture, all organic material has to be destroyed in the tested food. So the sample is put in a special round-necked flask and concentrated nitric and hydrochloric acid is added.
• Acids do their work: The acids get rid of all the organic substances which burn up and are left as ashes. The ones that remain are heavy metals and inorganic substances. Contaminants like pesticides, if present in the sample, are reduced to only their heavy metal components.
• Continuous measurements: Weight and volume is measured at different points in time, especially before and after testing. This determines the weight of different contents in the food sample.
• Spectrometry: Lead determination in foods generally requires a graphite furnace. This is where an instrument called the atomic absorption spectrophotometer (AAS) comes in. This instrument, used in most NABL-accredited labs, works on the principle that free atoms will absorb light at frequencies or wavelengths that are identified with specific elements. By observing these frequencies, one can ascertain the presence of the elements in question, for instance, lead. However, Nestle, for the purpose of testing heavy metals, uses a method called Inductively Coupled Plasma Mass Spectrometry. Traces of lead in food can be detected by any of these instruments.
• Small samples: An AAS instrument combines flame, furnace and vapour techniques to analyse food samples of a large number of toxic trace elements across a wide analytical range, from parts per million to subparts per billion. The furnace is also able to carry out analyses with a very small sample volume, as little as a few microlitres.