Boehm M F, Bada J L
Proc Natl Acad Sci U S A. 1984 Aug;81(16):5263-6. doi: 10.1073/pnas.81.16.5263.
The racemization half-lives (i.e., the time required to reach a D/L = 0.33) at pH 6.8 for aspartic acid and phenylalanine in the sweetener aspartame (L-aspartyl-L-phenylalanine methyl ester) were determined to be 13 and 23 hours, respectively, at 100 degrees C. Racemization at this pH does not occur in aspartame but rather in its diketopiperazine decomposition product. Our results indicate that the use of aspartame to sweeten neutral pH foods and beverages that are then heated at elevated temperature could generate D-aspartic acid and D-phenylalanine. The nutritive consequences of these D-amino acids in the human diet are not well established, and thus aspartame should probably not be used as a sweetener when the exposure of neutral pH foods and beverages to elevated temperatures is required. At pH 4, a typical pH of most foods and beverages that might be sweetened with aspartame, the half-lives are 47 hours for aspartic acid and 1200 hours for phenylalanine at 100 degrees C. Racemization at pH 4 takes place in aspartame itself. Although the racemization rates at pH 4 are slow and no appreciable racemization of aspartic acid and phenylalanine should occur during the normal use of aspartame, some food and beverage components could conceivably act as catalysts. Additional studies are required to evaluate whether the use of aspartame as a sugar substitute might not in turn result in an increased human consumption of D-aspartic acid and D-phenylalanine.
在100℃下，测定了甜味剂阿斯巴甜（L-天冬氨酰-L-苯丙氨酸甲酯）中，天冬氨酸和苯丙氨酸在pH 6.8时的消旋半衰期（即达到D/L = 0.33所需的时间），分别为13小时和23小时。在该pH值下，阿斯巴甜本身不会发生消旋，而是其环二肽分解产物发生消旋。我们的结果表明，使用阿斯巴甜来为中性pH值的食品和饮料增甜，随后再进行高温加热，可能会生成D-天冬氨酸和D-苯丙氨酸。这些D-氨基酸在人类饮食中的营养后果尚未明确，因此，当需要将中性pH值的食品和饮料暴露于高温时，阿斯巴甜可能不应被用作甜味剂。在pH 4（阿斯巴甜可能用于增甜的大多数食品和饮料的典型pH值）时，100℃下天冬氨酸的半衰期为47小时，苯丙氨酸的半衰期为1200小时。在pH 4时，阿斯巴甜本身会发生消旋。尽管pH 4时的消旋速率较慢，在阿斯巴甜的正常使用过程中，天冬氨酸和苯丙氨酸不会发生明显的消旋，但某些食品和饮料成分可能会起到催化作用。需要进一步研究来评估，将阿斯巴甜用作糖替代品是否反而会导致人类对D-天冬氨酸和D-苯丙氨酸的摄入量增加。
