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April 2020 ¦ international-dairy.com · 21
ing. It is also robust and therefore easy to use and to manipulate. However,
PDMS is hydrophobic and needs to be treated with chemicals to
make it hydrophilic like the human tongue. Given the effect of these
chemicals is only temporary, it is a challenge to ensure PDMS has good
“wettability” – so that any liquids applied have maximum contact with
the surface – and therefore make it more like the tongue.
These problems with the wettability of PDMS can be avoided by
using materials that are naturally hydrophilic. One such material is a gel
made from whey protein isolate (WPI). Previous tribometer measurements
comparing plates with surfaces made from different materials
have indicated that WPI may be more accurate than PDMS in imitating
the conditions in the mouth. To test whether or not WPI gel is more
suitable than PDMS for measuring friction forces in food, researchers
from DSM and NIZO have now compared the two materials in terms of
their ability to predict the creaminess of yogurt.
WPI gel better than PDMS
In this new study, the researchers first selected nine supermarket yogurts
ranging in fat content from 0 to 4.1% and asked a trained test
panel of 12 subjects to score them in terms of creaminess. They then
used a tribometer to analyse the yogurts using both WPI gel plates and
commercially available PDMS plates. They looked at the ability of the
surface materials to discriminate between the yogurts as well as the
repeatability of the experiments. Their results showed that WPI gel was
consistently better than PDMS at discriminating between the yogurts
in terms of friction behaviour. Besides determining the correlation between
friction and creaminess, they also determined the optimal range
for the sliding speed of the tribometer at which the method using WPI
gel plates can best discriminate between the different products.
Innovative food product development
The researchers hope this new application of WPI gels can now be
developed further for wider use. Given that different types of tribometers
make use of different plates, standard WPI gel plates will
need to be developed for different devices, and although WPI gel is
flexible and naturally hydrophilic, preparation of the gel sheets still
requires further optimisation. NIZO would therefore be interested
in hearing from potential industrial partners interested in collaborating
on a project to continue developing this technique.
Finally, looking more widely at innovative food product development,
this publication provides a prime example of how products
can be screened in the lab for mouthfeel defects, thereby
helping to speed up product development. We anticipate that such
screening methods and materials can also be used to screen for
other physical properties of food such as astringency.
References
1. Di Cicco F, Oosterlinck F, Tromp H and Sein A (2019) Comparative
study of whey protein isolate gel and polydimethylsiloxane
as tribological surfaces to differentiate friction properties of
commercial yogurts. Food Hydrocolloids 97, 105204. https://
doi.org/10.1016/j.foodhyd.2019.105204
2. Dresselhuis DM, De Hoog EHA, Cohen Stuart MA and Van Aken
GA (2008) Application of oral tissue in tribological measurements
in an emulsion perception context. Food Hydrocolloids 22,
323–335. https://doi.org/10.1016/j.foodhyd.2006.12.008
3. Joyner HS, Pernell CW and Daubert CR (2014) Beyond surface
selection: The impact of different methodologies on tribological
measurements. Journal of Food Engineering 134, 45–58
https://doi.org/10.1016/j.jfoodeng.2014.03.003
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