High true ileal digestibility but not postprandial utilization of nitrogen from bovine meat protein in humans is moderately decreased by high-temperature, long-duration cooking1-3

Abstract

Background: Meat protein digestibility can be impaired because of indigestible protein aggregates that form during cooking. Whenthe aggregates are subsequently fermented by themicrobiota, they can generate potentially harmful compounds for the colonicmucosa.Objective: This study evaluated the quantity of bovine meat protein escaping digestion in the human small intestine andthe 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 tubepositioned at the ileal level. They received a test meal exclusively composed of 120 g of intrinsically 15N-labeled bovinemeat, cooked either at 55° C for 5 min (n = 8) or at 90° C for 30 min (n = 8). Ileal effluents and blood and urine samples werecollected over an 8-h period after the meal ingestion, and 15N enrichments were measured to assess the digestibility ofmeat proteins and the transfer of dietary nitrogen into the metabolic pools.Results: Proteins tended to be less digestible for the meat cooked at 90° C for 30 min than at 55° 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 digesta did not differbetween 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 nitrogenlost through deamination did not differ between groups (21.2% ± 0.8% of ingested N).Conclusions: Cooking bovinemeat at a high temperature for a long time can moderately decrease protein digestibility comparedwith 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.