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

University of Illinois, Urbana, Illinois 61801

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.

KEY WORDS: • Maillard reaction • fructose-phenylalanine • Amadori product

¹ Gerber Inc., Fremont, Michigan.

² Department of Animal Science, University of Illinois.

³ Department of Food Science; author to whom all inquiries should be addressed.

⁴ Supported, in part, by the Illinois Agricultural Experiment Station, Urbana, Illinois.

Manuscript received 13 July 1978.