| The water activity and pH of a food system influence the shelf life of the product from the standpoint of microbial deterioration and chemical degradation of ingredients. It is often assumed that the pH of a reduced-moisture food system differs insignificantly from its fully hydrated state. However, this is not necessarily true. Thus, the objectives of this research project were to estimate changes of pH associated with dehydration of food systems and how this pH could affect chemical reactions occurring in the reduced-moisture food system.;The numerous traditional methods for measuring the pH of dehydrated systems each gave a different pH value, indicating the questionability of these methods. Concentrated buffer solutions and non-ionic solute solutions indicated the pH of phosphate buffer solutions decreased while that of citrate buffer solutions remained more constant. The pH-dependent degradation mechanisms and kinetics of aspartame and ampicillin enable the use of these compounds as pH markers in reduced-moisture solid systems. Aspartame degradation and ampicillin degradation indicated that the pH of reduced-moisture solid systems containing phosphate buffer was lower than in the hydrated state. As dehydration occurred and the pH of the system changed, the mechanisms of degradation changed as noted by the formation of different degradation products and their ratios. Reaction rates may be faster or slower than predicted based on water activity alone which has definite implications on predicting product stability in reduced-moisture systems. |
