High True Ileal Digestibility but Not Postprandial Utilization of Nitrogen from Bovine Meat Protein in Humans Is Moderately Decreased by High-Temperature, Long-Duration Cooking

Background: Meat protein digestibility can be impaired because of indigestible protein aggregates that form during cooking. When the aggregates are subsequently fermented by the microbiota, they can generate potentially harmful compounds for the colonic mucosa. Objective: This study evaluated the quantity of bovine meat protein escaping digestion in the human small intestine and the metabolic fate of exogenous nitrogen, depending on cooking processes. Methods: Sixteen volunteers (5 women and 11 men; aged 28 +/- 8 y) were equipped with a double lumen intestinal tube positioned at the ileal level. They received a test meal exclusively composed of 120 g of intrinsically N-15-labeled bovine meat, cooked either at 55 degrees C for 5 min (n = 8) or at 90 degrees C for 30 min (n = 8). Ileal effluents and blood and urine samples were collected over an 8-h period dfter the meal ingestion, and N-15 enrichments were measured to assess the digestibility of meat proteins and the transfer of dietary nitrogen into the metabolic pools. Results: Proteins tended to be less digestible for the meat cooked at 90 degrees C for 30 min than at 55 degrees C for 5 min (90.1% +/- 2.1% vs. 94.1% +/- 0.7% of ingested N; P = 0.08). However, the particle number and size in ileal digests did not differ between groups. The appearance of variable amounts of intact fibers was observed by microscopy. The kinetics of 15N appearance in plasma proteins, amino acids, and urea were similar between groups. The amount of exogenous nitrogen lost through deamination did not differ between groups (21.2% +/- 0.8% of ingested N). Conclusions: Cooking bovine meat at a high temperature for a long time can moderately decrease protein digestibility compared with cooking at a lower temperature for a short time and does not affect postprandial exogenous protein metabolism in young adults. The study was registered at www.clinicaltrials.gov as NCT01685307.