| Summary: | 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 (<b>1</b>) a rearrangement, (<b>2</b>) a hydration, and (<b>3</b>) an epoxidation/rearrangement product. Using deuterium-labeled water (D<sub>2</sub>O) experiments, compounds <b>1</b>–<b>2</b> 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<sub>1</sub> elimination on C15 to form the more thermodynamically stable trisubstituted alkene (compound <b>1</b>), or by the Markovnikov addition of water via SN<sub>1</sub> substitution to form a tertiary alcohol (compound <b>2</b>). Compound <b>3</b> 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 (<i>p</i> < 0.0001) the concentrations of compounds <b>1</b>–<b>2</b> compared to the aged control by 89 and 83%, respectively, whereas a specific coffee flavor and caramel color were reported to significantly reduce (<i>p</i> < 0.0001) the formation of compound <b>3</b> compared to the aged control during storage by 90 and 79%, respectively.
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