THOMAS KUNZ (1), Eon-Jeong Lee (1), Victoria Schiwek (1), Torsten Seewald (1), Frank-Jürgen Methner (1)
(1) Berlin Institute of Technology (TU Berlin), Department of Biotechnology, Chair of Brewing Sciences, Berlin, Germany
The properties and the mode of action of functional carbohydrates in
low-pH beverages such as juice, wine, beer, etc. is becoming more and
more a center of attention. The properties of reducing sugars are
interesting for shelf life, human nutrition, and the brewing process,
especially during wort boiling where sugar reactions are accelerated.
During the last decades, various research groups applied different
methods to ascertain the reducing potential of sugars. In comparison to
the traditional Fehling method, the method according to Chapon and Louis
is published (M. Moll, 2001) to be inapplicable for determining the
sugars’ reducing power. This method describes the reducing power of
beverages against a complex of Fe3+ with 2´,2´-dipyridyl. Our
research work proved that the proposed analytical parameters for the
Chapon method—concentration, temperature (20/25°C), and time (300 s)—are
unqualified. However, varying different parameters, like temperature
(80°C) and concentration, showed that the basic reaction mechanism of
the Fe3+ reduction is able to differentiate reducing
potentials between different sugars in low-pH areas. The functional
principle can be used to achieve information about the behavior of
sugars at different temperatures and during storage of beverages. In
analogy to the accelerating aging trials, an optimized Chapon method
using a temperature of 60°C (1 h) was developed. Sugars in low-pH
beverages behave differently than the generally known behavior described
by Fehling when using NaOH in the Fehling II solution. The applications
of the optimized method demonstrate that in a low-pH area (4.2), the
strongest reducing potential results from isomaltulose (Palatinose®), followed by fructose, trehalulose (Vitalose®), and maltotriose. Additional investigations using the reaction mechanism according to Fehling (Cu2+)
in this pH area showed similar results. At low pH, the formation of the
open-chain aldehyde structure of glucose is inhibited. In contrast,
fructose possesses a higher ability to generate the open-chain structure
at low pH resulting in much stronger reducing properties. The results
also show that sucrose has a higher reducing potential against Fe3+
than glucose. The increasing reducing potential of the “non-reducing
sugar” sucrose at low pH can be explained by the acid hydrolyzed
formation of invert sugar and the strong reducing potential of the
formed fructose. Other investigations at higher temperatures (80/90°C)
and higher pH (5.1) give evidence about the behavior of fermentable
sugars during wort boiling. Besides the described mode of action of
glucose, fructose, and sucrose, the stronger reducing potential of
maltotriose against maltose is remarkable. Finally, the optimized Chapon
method can be used to support the investigation of the complex reaction
mechanism of different sugars in beverages (juice, wine, beer) and the
brewing process.
After qualifying as a certified technician in preservation
engineering (1991–1993), Thomas Kunz completed his basic studies in
chemistry at the University of Applied Sciences, Isny (1994–1995), and
his basic studies in food chemistry at Wuppertal University (1995–1998),
before starting to study food technology at the University of Applied
Sciences, Trier (1998–2002). After graduating, he worked as a chartered
engineer in the area of ESR spectroscopy at the Institute of Biophysics
at Saarland University (2002–2004). Since 2005, he has been employed as a
Ph.D. student at the Research Institute of Brewing Sciences, Berlin
Institute of Technology (Technische Universität Berlin). His main
research focus lies in analyzing radical reaction mechanisms in beer and
other beverages using ESR spectroscopy.
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