Reducing Properties of Fermentable and Nonfermentable Carbohydrates in Beverages and Brewing Process

Abstract

An optimized method to ascertain the reduction potential of sugars against Fe3+ at low pH range was applied to get a deeper insight into the reduction properties of carbohydrates in beverages and during the brewing process. Our investigations have clearly shown that the behavior of carbohydrates at low pH is different compared with the generally known reduction properties described by Fehling using NaOH. At a low pH range, the formation of the open-chain aldehyde structure of glucose is more inhibited and fructose has a higher ability to generate the open structure, resulting in stronger reducing properties. At typical beer pH range of approx. 4.3, the analyses showed the strongest reduction potential caused by the nonfermentable carbohydrate isomaltulose, which is commercially used to increase the palate fullness of beverages. On the side of fermentable carbohydrates, fructose showed the strongest reduction potential followed by maltotriose and maltose. The detected higher reduction potential of the “nonreducing” sucrose contrary to the so-called “reducing sugar” glucose can be explained by the acid hydrolyzation of carbohydrates. Furthermore, the demonstrated pH-dependent changes of the reduction potentials of carbohydrates, are notable and help to explain the influences of carbohydrates on oxidative processes at different pH ranges of beverages. Analogous to the latest publications about influences of substances with typical reductone or enediol structure on the acceleration of oxidative processes, the increasing reduction potential of carbohydrates is responsible for an accelerated oxygen activation and radical generation. Especially during the wort boiling process, where all carbohydrate reactions are accelerated, the carbohydrates with the stronger reduction potential are responsible for a stronger acceleration of oxidative processes and vice versa.