Cooking science in the lab

In cooking, agar is widely used in Asian desserts such as agar-agar.

To make agar-agar, a mixture of agar, sugar and water is brought to a boil before being cooled in a container to make jelly.

But this jelly-like substance also has its use in microbiology - both for research and clinical purposes.

It is the main ingredient for making "agar plates" - petri dishes with solid agar as a surface for bacteria and other microbes to grow on. But microbes are difficult to "culture" or grow in the laboratory due to their specific growth requirements. Sometimes, other ingredients are added to the agar so that microbes can grow and reproduce on the agar plate.

For example, Streptococcus pneumoniae - the culprit behind pneumonia - needs blood to be in the agar. The blood, which usually comes from sheep or horses, has an enzyme called catalase, which neutralises the acidity of hydrogen peroxide produced by the bacteria. Without this enzyme, the agar environment can be too acidic for the bacteria to grow properly.

And once sufficient amounts of bacteria grow on the plate, microbiologists can isolate colonies of the bacteria for further study.

In clinical practice, agar plates are used, together with biochemical tests, to identify microbes that might have been the cause of a food poisoning outbreak.

In the lab, microbes from a contaminated food sample are cultured on an agar plate that generally supports the growth of most microbes. Then, colonies of these microbes are transferred to other different kinds of agar plates which permit only the growth of certain microbes. For example, the blood agar differentiates the presence of Streptococcus pneumoniae from other bacteria.

Once the suspect has been identified, biochemical tests will be carried out on the microbe to confirm the culprit.

A version of this article appeared in the print edition of The Straits Times on June 21, 2018, with the headline 'Cooking science in the lab'. Print Edition | Subscribe