Nutritional Implications of the Maillard Reaction. The Metabolism of Fructose-Phenylalanine in the Rat

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Abstract
Experiments were conducted with rats to evaluate the absorption efficiency and metabolism of fructose-phenylalanine (F-Phe) the Amadori compound resulting when glucose reacts with phenylalanine (Phe). Fructose-[U-14C]phenylalanine was given via either stomach tube or intraperitoneal injection (ip). One rat was killed at various time periods up to 48 hours after dosing. When stomach intubated, 14C absorption was observed to be much slower with F-[U-14C]Phe than [U-14C]Phe. Excretion of radioactivity in expired air and urine reached a peak within 2 hours when [U-14C]Phe was administered, but it took 48 hours for 80% of the administered radioactivity from F-[U-14C]Phe to be similarly excreted. High levels of antibacterial substances in the diet had no effect on the rate of Phe absorption, but the effect on the absorption of 14C from F-Phe was dramatic. Only 2.3% of the administered radioactivity from F-Phe was found in expired CO2 after 48 hours as compared with 10.4% in non-antibiotic fed controls. Over the same time interval, only 15.9% of the dose was detected in urine compared with 70% in controls. When F-[U-14C]Phe was injected ip into non-antibiotic fed rats, only 1.1% of the administered dose appeared as expired CO2 after 48 hours. Urinary excretion, however, was very rapid, with 80% of the administered dose being excreted within 3 hours after injection. It appears, therefore, that (1) F-Phe is poorly absorbed, (2) what little is absorbed is dependent upon the gut microflora, and (3) most of the radioactivity from F-[U-14C]Phe observed to cross the gut results from microbially produced products.