|Rebaudioside A is a non-caloric high intensity sweetener extracted from Stevia rebaudiana. For it to be used in the food industry, rebaudioside A needs to be stable during processing and storage. Kinetic data on its long term stability as affected by solution composition are lacking. The primary objective of this study was to evaluate the storage stability of rebaudioside A in various buffer solutions as a function of pH, buffer type, buffer concentration and temperature. The effect of light exposure on rebaudioside A stability was also evaluated.
Rebaudioside A solutions were prepared in 0.02 and 0.1 M phosphate and citrate buffers at pH 3, 5 and 7. Duplicate samples were stored at 20, 30 and 40 °C. Some samples were stored at room temperature under light or dark conditions. Aliquots were removed nine times for approximately nine months. The concentrations of rebaudioside A were analyzed and pseudo-first-order rate constants with 95% confidence intervals were calculated for the loss of rebaudioside A.
In phosphate buffer, the degradation of rebaudioside A was generally faster at higher pH values. The pH effect on rebaudioside A stability was generally reversed in citrate buffer. Rebaudioside A broke down significantly faster in phosphate buffer than in citrate buffer at pH 5 and 7; degradation rates were similar at pH 3. Higher buffer concentrations promoted faster degradation. Rebaudioside A degradation was accelerated by the elevation of temperature. The exposure of light did not have an obvious effect in phosphate buffer at pH 7 while it lowered the stability of rebaudioside A in citrate buffer at pH 3.
For optimum stability of beverages containing rebaudioside A, lower temperatures and lower buffer concentrations are preferred. If the product has a pH value of 5 or 7, citrate buffer is more preferred than phosphate. Dark environments help stabilize rebaudioside A in beverage at pH 3.