Kinetics of an Acid‐Base Catalyzed Reaction (Aspartame Degradation) as Affected by Polyol‐Induced Changes in Buffer pH and pK_a Values

Abstract

The kinetics of an acid-base catalyzed reaction, aspartame degradation, were examined as affected by the changes in pH and pK a values caused by adding polyols (sucrose, glycerol) to phosphate buffer. Sucrosecontaining phosphate buffer solutions had a lower pH than that of phosphate buffer alone, which contributed, in part, to reduced aspartame reactivity. A kinetic model was introduced for aspartame degradation that encompassed pH and buffer salt concentrations, both of which change with a shift in the apparent pK a value. Aspartame degradation rate constants in sucrose-containing solutions were successfully predicted using this model when corrections (that is, lower pH, lower apparent pK a value, buffer dilution from the polyol) were applied. The change in buffer properties (pH, pK a ) from adding sucrose to phosphate buffer does impact food chemical stability. These effects can be successfully incorporated into predictive kinetic models. Therefore, pH and pK a changes from adding polyols to buffer should be considered during food product development.