DIGESTIBILITY OF COOKED AND RAW EGG PROTEIN IN HUMANS AS ASSESSED BY STABLE-ISOTOPE TECHNIQUES

Egg proteins contribute substantially to the daily nitrogen allowances in Western countries and are generally considered to be highly digest ible. However, information is lacking on the true ileal digestibility of either raw or cooked egg protein. The recent availability of stable isotope-labeled egg protein allowed determination of the true ileal d igestibility of egg protein by means of noninvasive tracer techniques. Five ileostomy patients were studied, once after ingestion of a test meal consisting of 25 g of cooked C-13- and N-15-labeled egg protein, and once after ingestion of the same test meal in raw form. Ileal effl uents and breath samples were collected at regular intervals after con sumption of the test meal and analyzed for N-15- and C-13-content, res pectively. The true ileal digestibility of cooked and raw egg protein amounted to 90.9 +/- 0.8 and 51.3 +/- 9.8%, respectively. A significan t negative correlation (r = -0.92, P < 0.001) was found between the C- 13-recovery in breath and the recovery of exogenous N in the ileal eff luents. In summary, using the N-15-dilution technique we demonstrated that the assimilation of cooked egg protein is efficient, albeit incom plete, and that the true ileal digestibility of egg protein is signifi cantly enhanced by heat-pretreatment. A simple C-13-breath test techni que furthermore proved to be a suitable alternative for the evaluation of the true ileal digestibility of egg protein.