Laser-speckle method detects bacteria on food in seconds

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Researchers from the Korea Advanced Institutes of Science and Technology (KAIST) in South Korea have developed a low-cost method for detecting bacteria on the surface of foods in just a few seconds. According to the researchers, the laser speckle technique could be used in food processing lines or even inside home refrigerators.

Food poisoning is a potentially lethal condition that poses a serious problem for the food industry. The current methods for detecting bacteria in food products – such as microbiological culturing, polymerase chain reactions, liquid chromatography, and mass spectrometry – are complex, time consuming, and require trained professionals. As a result, many food companies do not have access to these kind of techniques.

The new method developed by KAIST researchers focuses on detecting the movement caused by bacteria propelling themselves across surfaces. A red, 633nm laser beam is fired onto the food’s surface, where it is scattered, creating a laser speckle pattern.

Because the bacteria on the surface of food also scatter light, as the bacteria move the speckle pattern changes. So, by detecting the decorrelation in the laser speckle intensity patterns from tissues, the living activities of microorganisms can be detected.

A camera with a speed of 30 frames per second is also used to record this movement over a few seconds.

As part of their development, the researchers tested their technique on a chicken breast contaminated with the common bacteria Escherichia coli and Bacillus cereus.

The experiment revealed which samples were contaminated and to what degree. Both types of bacterial contamination were detected – although the technique couldn’t distinguish between them – and the uncontaminated meat showed little or no change in the laser speckle pattern over time.

Although the technique seems promising, it does have certain limitations, such as not being able to distinguish between different types of bacteria, and not recognising toxins produced by bacteria, which can cause illness even after the bacteria have been killed off.

However, the laser speckle monitoring technique provides a simpler and faster way of detecting bacteria than existing methods, and it only requires cheap equipment that could potentially be fitted onto food processing lines or even inside home refrigerators in the future.

Furthermore, the method does not require contact with food products and so can be carried out remotely. It can also see through transparent plastic packaging, which does not influence the speckle pattern.

Further information 

A simple and rapid method for detecting living microorganisms in food using laser speckle decorrelation