By Michael
Irving
March 02, 2021
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Researchers in Japan have developed a contactless way to measure the ripeness of
soft fruit like mangoes Photo credit:
elxeneize/Depositphotos
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Firmness is one of the most
reliable indicators of ripeness, but it’s time-consuming (not to mention
unhygienic) for everyone along the chain to give it a squeeze. Plus, soft fruits
can be damaged by repeated handling and pressure.
So the team on the new study set
out to come up with a contactless method to measure ripeness. The researchers
used a high-intensity laser to create a bubble of plasma near the surface of
mangoes. As the plasma bubble expands it produces shockwaves, which in turn
create vibrations across the fruit. An instrument called a laser Doppler
vibrometer (LDV) can then measure those vibrations and infer the firmness, and
by extension the ripeness, of the fruit.
Similar methods have been used
before to, for example, check the ripeness
of avocados, but that involved mechanically striking the fruit, which
doesn’t work as well on softer fruit like mangoes.
A diagram of how the new fruit
ripeness measuring device works Shibaura Institute of Technology
The SIT researchers previously
used their plasma method on apples, but again, it didn’t work on soft fruit
because they don’t produce the right type of vibrations. For this new study, the
team found that plasma shockwaves can create a type of vibration called Rayleigh
waves, which only propagate across the surface.
Tests revealed that these
Rayleigh waves could still indicate firmness and ripeness with the help of the
LDV. The results were clearer when the waves were sent around the “equator” of
the mango, rather than along the vertical axis. This seems to be because of the
seeds in the center.
The team did point out that the
measurements can be thrown off by cavities inside the flesh or by decay. In
future work the researchers plan to continue investigating how to get around
these problems by targeting different parts of the fruit, and hopefully
extending the method to other soft fruits.
Other contactless methods to
measure ripeness include sensors and handheld
"electronic noses" that can detect specific compounds that fruit gives off
as it ripens.
The new research was published in
the journal Food.
Source: Shibaura
Institute of Technology