Characterization of the Flavor Stability of Rebaudioside A in Beverage Systems

Autor: Gelinas, Benjamin Scott
Jazyk: angličtina
Rok vydání: 2021
Předmět:
Druh dokumentu: Text
Popis: Reducing added dietary sugar intake is needed for the better health, leading to longer lifespan, less prevalence of preventable diseases, and better overall wellness. A common practice for reducing added calories, while maintaining sweetness, is to replace caloric sweetener ingredients with non-nutritive, high intensity sweeteners; however, consumer opinions of high intensity sweeteners remain a challenge, due to lower flavor quality, and often artificial compounds utilized. There has been an increased use of plant-based high intensity sweeteners, such as those found within the leaves of Stevia rebaudiana, which contain a variety of highly sweet di-terpene glycosides called rebaudiosides and steviosides. The most used stevia-based sweetener is Rebaudioside A (Reb A) driven primarily by its high relative sweetness intensity, large abundance in the plant leaves, and relatively clean taste. However, the use of stevia sweeteners is limited by lower flavor performance compared to common nutritive sweeteners. An improved understanding of the chemical drivers of stevia flavor is needed. The overall aim of this dissertation was to define the impact of storage on the flavor stability of Reb A in beverage systems. This research consisted of two phases: (1) to define the impact of Reb A degradation on the flavor profile and (2) to investigate mechanisms of Reb degradation. In the first phase of the project, untargeted LC-MS flavoromic chemical profiling was used to identify compounds related to sensory change in Reb A sweetened beverages during storage. Beverage samples consisting of 80%, 90% and 98% purity Reb A were stored under accelerated conditions for six weeks at 35 ⁰C. Good quality orthogonal partial least squares analysis (OPLS) models were developed from the chemical profiles and the d’ values from tetrad sensory testing with reasonable predictive ability. Four highly predictive compounds were selected based on VIP scores consisting of three positively correlating compounds and one negatively correlating compound. Based on accurate mass and NMR analysis, the compounds were identified as Reb A (negatively correlated) and three Reb A degradation compounds (positively correlated), that included a rearrangement, a hydration, and an epoxidation/rearrangement of Reb A, termed compounds 1, 2 and 3, respectively. The concentrations of compounds 1-3 in the stored beverages were determined to be below the sensory best estimate recognition threshold values. However further sensory recombination testing of the three compounds as a mixture revealed a perceivably significant sensory change. Thus, Reb A degradation products have an additive-type sub-threshold activity which causes a shift in perception in both unsweetened and sweetened beveragesThe second phase investigated the pathways of rebaudioside A (Reb A) degradation in acidic beverages during storage. Three degradation products of known sensory importance were monitored that included a rearrangement, a hydration, and an epoxidation/rearrangement of Reb A, termed compounds 1, 2 and 3, respectively. Using deuterium labeled water (D2O) experiments, compounds 1-2 were reported to be generated by acid-catalyzed mechanisms involving the carbocation on carbon position 16 (C16), followed by either proton elimination on C15 to form the more thermodynamically stable alkene (compound 1) or by the Markovnikov addition of water to form a tertiary alcohol (compound 2). Compound 3 was generated by the epoxidation of the alkene at C16-17 position, followed by ring opening and rearrangement to form a new alkene bond between C15-C16 and a primary alcohol on C17. Further analysis of beverage ingredients on the formation of compounds 1-3 indicated the addition of caramel color significantly increased the concentration of compounds 1-2, whereas the flavoring material (coffee) and caramel color were reported to significantly reduce the formation of compound 3 during storage. In summary, three Reb A degradation compounds were identified as key chemical changes during storage that impacted the flavor stability of beverage systems. Two mechanisms of degradation were reported, an acid-catalyzed carbocation intermediate pathway and an epoxidation/rearrangement pathway both involving the exomethylene functional group of Reb A. Further analysis also demonstrated the addition of caramel color and added flavor materials significantly altered the formation of these Reb A degradation compounds. Overall, this work provides a basis to improve the performance of Reb A by providing chemical markers to monitor Reb A flavor stability and an improved understanding of the mechanisms of degradation, ultimately to increase market utilization.
Databáze: Networked Digital Library of Theses & Dissertations