Digestibility of Cooked and Raw Egg Protein in Humans as Assessed by Stable Isotope Techniques

Manuscript received 6 October 1997. Initial reviews completed 18 November 1997. Revision accepted 3 June 1998.

Department of Medicine, Division of Gastroenterology and Gastrointestinal Research Centre, University Hospital Leuven, B-3000 Leuven, Belgium

Egg proteins contribute substantially to the daily nitrogen allowances in Western countries and are generally considered to be highly digestible. 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 digestibility 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 ¹³C- and ¹⁵N-labeled egg protein, and once after ingestion of the same test meal in raw form. Ileal effluents and breath samples were collected at regular intervals after consumption of the test meal and analyzed for ¹⁵N- and ¹³C-content, respectively. The true ileal digestibility of cooked and raw egg protein amounted to 90.9 ± 0.8 and 51.3 ± 9.8%, respectively. A significant negative correlation (r = 0.92, P < 0.001) was found between the ¹³C-recovery in breath and the recovery of exogenous N in the ileal effluents. In summary, using the ¹⁵N-dilution technique we demonstrated that the assimilation of cooked egg protein is efficient, albeit incomplete, and that the true ileal digestibility of egg protein is significantly enhanced by heat-pretreatment. A simple ¹³C-breath test technique furthermore proved to be a suitable alternative for the evaluation of the true ileal digestibility of egg protein.

The Journal of Nutrition Vol. 128 No. 10 October 1998, pp. 1716-1722
Copyright ©1998 by the American Society for Nutritional Sciences

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