Presenter: Thomas Kunz, Berlin Institute of Technology, Department of Biotechnology, Chair of Brewing Science, Berlin, Germany. Coauthor(s): Eon-Jeong Lee, Torsten Seewald, Victoria Schiwek, and Frank-Jürgen Methner, Berlin Institute of Technology, Department of Biotechnology, Chair of Brewing Science, Berlin, Germany.
The properties of reducing sugars are interesting for the shelf life of beverages, human nutrition, and the brewing process, especially during wort boiling, where the sugar reactions are accelerated. During the last decades, various research groups have applied different methods to ascertain the reducing potential of sugars. In comparison to the traditional Fehling method, the method according to Chapon and Louis to determine the reducing potential of beer and wort is not applicable for determining the reducing power of sugars. 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. To emulate the accelerated aging trials, an optimized Chapon method using a temperature of 60°C (1h) 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, 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 EPR spectroscopy at the Institute of Bio Physics at Saarland University (2002–2004). Since January 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 EPR spectroscopy.