Mechanisms of Rebaudioside A Degradation and Ingredient-Sweetener Interactions in Beverages during Storage.

The instability of rebaudioside A (Reb A) in food product applications during storage challenges their utilization. The pathways of Reb A degradation in aged acidic beverages were investigated. Three Reb A degradation compounds of known sensory importance were monitored, consisting of ( 1 ) a rearrangement, ( 2 ) a hydration, and ( 3 ) an epoxidation/rearrangement product. Using deuterium-labeled water (D 2 O) experiments, compounds 1 - 2 were reported to be generated by acid-catalyzed mechanisms involving the formation of a carbocation on carbon position 16, followed by either deprotonation via E 1 elimination on C15 to form the more thermodynamically stable trisubstituted alkene (compound 1 ), or by the Markovnikov addition of water via SN 1 substitution to form a tertiary alcohol (compound 2 ). Compound 3 was generated by epoxidation of the exomethylene at the C16-17 positions, followed by the opening and rearrangement of the ring to form a new alkene bond between C15-C16 and a primary alcohol on C17. Further analysis of the effect of beverage ingredients indicated the addition of caramel color significantly increased ( p < 0.0001) the concentrations of compounds 1 - 2 compared to the aged control by 89 and 83%, respectively, whereas a specific coffee flavor and caramel color were reported to significantly reduce ( p < 0.0001) the formation of compound 3 compared to the aged control during storage by 90 and 79%, respectively.