In addition, aspartylphenylalanine diketopiperazine begins to form. In that document they described in detail the many mistakes that were made by G.D. Searle when testing for aspartame's by-products and breakdown constituents. HPLC is a far superior analytical method relative to TLC and numerous HPLC methods exist for the detection and quantification of amino acids. . . . Other breakdown chemicals such as free methanol which were not included in the list above, appear in much larger amounts at temperatures over 145oF. It is not difficult to imagine that carbonated beverages being shipped in unairconditioned trucks or trains can be exposed to very high temperatures for significant periods of time. It is obvious that wharehouse and grocery store storage conditions can lead to significant temperatures or long storage times.
Many stores have diet sodas stacked outside of the cooler in direct sunlight.
Finally, a person, family, or group sometimes purchases large quanities of diet soda for indenfinate storage. The time from when the beverage was created to when it was ingested can be a significant length of time. I beleive that Pepsi is the only brand that stamps their date of expiration on their aspartame-containing products. Even in bottles where the expiration date has not passed, enough time has often elapsed for a significant amount of breakdown to occur. That study shows that during the summer months, soft drinks are often exposed to relatively high temperatures for certain time periods in the course of distribution from the bottling plant to the consummer.