Flying
in the face of years of scientific belief, University of Illinois
researchers have demonstrated that sugar doesn't melt, it decomposes.
"This
discovery is important to food scientists and candy lovers because it
will give them yummier caramel flavors and more tantalizing textures. It
even gives the pharmaceutical industry a way to improve excipients, the
proverbial spoonful of sugar that helps your medicine go down," said
Shelly J. Schmidt, a University of Illinois professor of food chemistry.
In
a presentation to the Institute of Food Technologists about the
importance of the new discovery, Schmidt told the food scientists they
could use the new findings to manipulate sugars and improve their
products' flavor and consistency.
"Certain
flavor compounds give you a nice caramel flavor, whereas others give
you a burnt or bitter taste. Food scientists will now be able to make
more of the desirable flavors because they won't have to heat to a
'melting' temperature but can instead hold sugar over a low temperature
for a longer period of time," she said.
Candy
makers will be able to use a predictable time-temperature relationship,
as the dairy industry does in milk pasteurization, to achieve better
results, she said.
Schmidt
and graduate student Joo Won Lee didn't intend to turn an established
rule of food science on its head. But they began to suspect that
something was amiss when they couldn't get a constant melting point for
sucrose in the work that they were doing.
"In
the literature, the melting point for sucrose varies widely, but
scientists have always blamed these differences on impurities and
instrumentation differences. However, there are certain things you'd
expect to see if those factors were causing the variations, and we
weren't seeing them," Schmidt said.
The scientists determined that the melting point of sugar was heating-rate dependent.
"We
saw different results depending on how quickly we heated the sucrose.
That led us to believe that molecules were beginning to break down as
part of a kinetic process," she said.
Schmidt
said a true or thermodynamic melting material, which melts at a
consistent, repeatable temperature, retains its chemical identity when
transitioning from the solid to the liquid state. She and Lee used
high-performance liquid chromatography to see if sucrose was sucrose
both before and after "melting." It wasn't.
"As soon as we detected melting, decomposition components of sucrose started showing up," she said.
To
distinguish "melting" caused by decomposition from thermodynamic
melting, the researchers have coined a new name—"apparent melting."
Schmidt and her colleagues have shown that glucose and fructose are also
apparent melting materials.
Another
of Schmidt's doctoral students is investigating which other food and
pharmaceutical materials are apparent melters. She says the list is
growing every day.
Having
disposed of one food science mystery, Schmidt plans to devote time to
others. For instance, staling intrigues her. "We could ship a lot more
food around the world if we could stabilize it, keep it from getting
stale," she said.
Or
there's hydrate formation, which can make drink mixes clumpy if they're
open for a while. "We've observed the results—clumping under conditions
of low relative humidity—but we really don't know why it happens," she
noted.
Schmidt
said that new instruments are making it possible to probe some of the
processes scientists have taken for granted in a way they couldn't do
before.
Four
studies describing Schmidt's research have been published in recent
issues of the
Journal of Agricultural and Food Chemistry. Co-authors of
the first, third, and fourth articles are Joo Won Lee of the U of I and
Leonard C. Thomas of DSC Solutions. Joo Won Lee, John Jerrell, Hao Feng,
and Keith Cadwallader, all of the U of I, and Leonard C. Thomas of DSC
Solutions co-authored the second article.
Recent related studies:
Can the Thermodynamic Melting Temperature of Sucrose, Glucose, and Fructose Be Measured Using Rapid-Scanning Differential Scanning Calorimetry (DSC)?Effects of Heating Conditions on the Glass Transition Parameters of Amorphous Sucrose Produced by Melt-QuenchingInvestigation of the Heating Rate Dependency Associated with the Loss of Crystalline Structure in Sucrose, Glucose, and Fructose Using a Thermal Analysis Approach (Part I)SOURCE