TALKING to plants to keep them healthy is considered crazy enough. But
listening to them? Well that鈥檚 exactly what researchers in Illinois propose
doing to weed out kernels of corn that could end up poisoning your breakfast.
Grain stores often become infected with fungi that produce harmful toxins, and
the food industry has to prevent such poisons ending up in cornflakes or animal
feed.
Current tests use ultraviolet light, which makes certain species of fungus
glow in the dark. Grains that fluoresce bright green-yellow are thrown away. The
trouble is that this BGYF test, as it鈥檚 known, misses around 15 per cent of
infected kernels.
So chemists Sherald Gordon and Richard Greene of the National Center for
Agricultural Utilization Research in Peoria, Illinois, have devised a more
accurate way to spot contaminated corn. They recognise infected grains by
listening for telltale noises made by mouldy kernels when they are bombarded
with an infrared strobe light.
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The strobe鈥檚 short pulses make kernels heat up and cool down very quickly,
says Greene. The dissipating heat produces sound waves which can be picked up by
a microphone. 鈥淐lean kernels absorb light and give off sounds at specific
wavelengths,鈥� Greene explains. 鈥淏ut fungi alter the kernels鈥� chemical and
physical structure.鈥� These changes mean infected kernels produce sounds at
slightly different wavelengths.
The researchers used a technique known as Fourier Transform Infrared
Photoacoustic Spectroscopy (FTIR-PAS) to record the kernels鈥� moans and groans,
which are analysed by neural network software written by computer scientist
Bruce Wheeler at the University of Illinois. 鈥淭he network achieves a 96 per cent
accuracy in spotting clean and contaminated corn. It鈥檚 definitely more sensitive
than the BGYF test,鈥� Greene says.
Because the technique works on single grains, Greene believes it should be
ideal for laboratory testing of suspicious samples鈥攖hough not for an
automated test in grain factories. For this the chemists are investigating a
similar technique called Transient Infrared Emission Spectroscopy (TIRS), which
is better for spotting infected kernels on a conveyor belt.
TIRS was devised by John McClelland of Iowa State University in Ames, who
realised that heated kernels also emit small amounts of infrared light at
specific wavelengths, and that these wavelengths vary depending on the health of
the grain. Because the emissions are short-lived, kernels can be heated and
tested with TIRS as they pass by on a factory production line.
Greene does not envisage either FTIR-PAS or TIRS replacing the fluorescence
test. 鈥淲e don鈥檛 know why yet but the different approaches seem to miss different
infected grains.鈥� A combination of the two could weed out even more of the
infected kernels, he says.