N-15-LABELED IMMUNOGLOBULINS FROM BOVINE COLOSTRUM ARE PARTIALLY RESISTANT TO DIGESTION IN HUMAN INTESTINE

To evaluate true ileal digestibility of bovine immunoglobulins, seven healthy human adults ingested N-15-labeled preparation of an immunoglo bulin concentrate. After fasting overnight, subjects drank 400 mL of i mmunoglobulin concentrate (77 mmol), and ileal effluents were collecte d for 8 h at 20-min intervals using a naso-intestinal intubation techn ique. In addition to osmolality and pH, the concentrations of exogenou s and endogenous nitrogen and ions (Na+, K+, Cl-, Ca2+, Mg2+) in the e ffluents were measured. Bovine immunoglobulin concentrations (IgG, IgM , IgA) were estimated by a radial immunodiffusion technique. The mean flow rate of the liquid phase was 22.3 +/- 6.1 mL/20 min and did not v ary significantly during the collection period. No change was observed for osmolality, pH or Na+, K+ and Cl- concentrations. Two hours after meal ingestion, Ca2+ and Mg2+ concentrations increased significantly (P < 0.05). The recoveries of nitrogen of ingested IgG and IgM still i mmunologically active were 19 +/- 3% and 19 +/- 4%, respectively. No I gA was detected in the ileum. Mean digestibility of the exogenous nitr ogen fraction was 79 +/- 3%. In comparison to literature data, which s how that other milk proteins have ileal digestibilities of >90%, our r esults demonstrate a lower ileal digestibility of bovine immunoglobuli ns in humans.