Influence of Intermediate Maillard Reaction Products with Enediol Structure on the Oxidative Stability of Beverages

Abstract

The influence of Maillard reaction products, originating from special malt, on the oxidative flavor stability of beverages was investigated by ESR methods (EAP determination, T500 values) and traditional methods according to MEBAK and Chapon to determine the reducing power or potential. Simultaneously, the color, SO2 content, and concentration of specific dicarbonyl compounds were determined (HPLC method). The aim of the study was to get a deeper insight into the antioxidative properties of wort and beer brewed with special malt and the influence of reductones/enediols as intermediate Maillard reaction products on the oxidative stability. The results show a direct correlation between the content of Maillard reaction products in malt and a higher reducing power or potential, if measured by Chapon or MEBAK method. In contrast to this, the same special malt leads to a higher radical generation in wort and the final beer (T500 values) and consequently to a lower oxidative stability (EAP value) measured by EPR spectroscopy. These contradictory results seem to be one reason why the influence of special malt on beer stability has been discussed controversially in literature. In further investigations, by addition of caramel color, malt extract, reductone solutions, and ascorbic acid to beer, it was possible to get more information on the properties of specific intermediate Maillard reaction products. The explanation of the described contradictory results arises from the strong reduction properties of Maillard reaction intermediate products with reductone/enediol structure. In analogy to the formation of reductones from fructose through 2,3-enediol and 1-deoxyosone, the formation of reductones from glucose is theoretically possible, in which 1,2-enediol is produced from glucosone catalyzed by the reduction of metal ions. These reductones/enediols can rapidly reduce oxidized metal ions like Fe+3 to Fe+2, resulting in an acceleration of oxygen activation (ROS, reactive oxygen species) and intensifying the Fenton/Haber-Weiss reaction system. Hence, a stronger radical generation of very reactive radicals (e.g., OH·) can be observed in the wort and beer matrix. The acceleration of the reaction system leads to a faster consumption of antioxidative substances, such as SO2, resulting in lower oxidative beer stability. Altogether, the results present the pro- and antioxidative effect of specific Maillard reaction intermediate products with reductone/enediol structure in beer and other beverages caused by the addition of special malts. Consequently, the use of special malts is a question of malt type and should be limited to the necessary addition for the adjustment of the desired color in the brewing process. Furthermore is the application of ascorbic acid addition, especially in combination with an SO2 addition, as an antioxidant component to improve the oxidative beer, to handle carefully.