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EAP Determination and Beverage Antioxidative IndeX (BAX) Advantageous Tools for Evaluation of the Oxidative Flavour Stability of Beer and Beverages (Part 1)
T. Kunz, C. Mller, F.-J. Methner

For the prediction of the beers flavour stability, the determination of the so-called lag-time using electron spin resonance spectroscopy (ESR) has become a standardized method. Previous investigations demonstrated that the lagtime measurement used up to now distorts the results of oxidative flavour stability due to an increasing pHvalue during the analysis caused by the spin trap reagent (PBN). Against this background, a new EAPdetermination was developed which excludes the distortions and provides a new index number for the evaluation of flavour stability; the Beverage Antioxidative indeX (BAX). As a complement to the EAP determination, the BAX provides additional information about the interplay of anti- and pro-oxidative beer ingredients independent of the SO2-content and about the consumption rate of the existing antioxidative potential during storage. In this study, the BAX determination was used to demonstrate the influence of pH, metal ions, α-acids, intermediates of Maillard reaction with reductone/endiol structure and adjuncts such as barley on the pro- and antioxidative properties of the beer matrices and beer flavour stability. The results could be used to describe the positive effect and mechanisms of α-acids and low pH-values on the oxidative beer stability. In context to the generally known strong reduction properties of intermediate Maillard reaction products such as reductones/endiols against oxidized metal ions, a significant pro-oxidative effect of reductones on the beer matrices could be demonstrated. The reaction mechanism is based on the strong pro-oxidative influences of metal ions like iron and their capability to activate oxygen and the catalytic effect on the radical generation caused by the Fenton-/Haber-Weiss reaction systems. Trials with addition of black coloured reductone solution to beer showed a strong decrease of BAX and EAP-values which indicate their negative influences on the beer matrix.

Descriptors: ESR spectroscopy, oxidative beer flavour stability, Fenton Reaction, SO2, reductones, iron

BrewingScience - Monatsschrift fr Brauwissenschaft, 66 (January/February 2013), pp. 12-22