NITROGEN MOVEMENTS IN THE UPPER JEJUNUM LUMEN IN HUMANS FED LOW AMOUNTS OF CASEIN OR BETA-LACTOGLOBULIN

Objectives and methods. - To compare the progression of milk proteins in the upper part of the digestive tract, gastro-jejunal nitrogen move ments were studied in 6 healthy human volunteers after beta-lactoglobu lin and casein ingestion. 400 mL of water (control), purified beta-lac toglobulin (20 g/L) or casein (20 g/L), each adjusted to 25 mu Ci with C-14-polyethylene glycol, were given per os. Samples were collected i n the stomach and 20 cm below the Treitz ligament every 20 min for 2 h ours and measured for volume, osmolarity, ions and nitrogen content. R esults. - The jejunal flow rare peaked in the 0-20 min period followin g water and beta-lactoglobulin ingestion, and in the 20-40 min period after casein ingestion. The gastric half-emptying time (T-1/2 min) of the liquid phase was significantly different (P < 0.05) for water (12. 1 +/- 0.8), P-lactoglobulin (14.5 +/- 3.3) and casein (26.5 +/- 9.3). Before ingestion of the test meals, the basal rate of nitrogen was 9.1 4 +/- 4.09 mmol/h in the jejunum. The total nitrogen content in the je junum peaked significantly in the 0-20 min period after beta-lactoglob ulin ingestion and the 20-40 min period after casein ingestion. The ap parent gastro-jejunal protein absorption values were 63 % for casein a nd 66 % for beta-lactoglobulin in the 120 min period. Conclusions. - T hese results show that beta-lactoglobulin and casein behave differentl y in the upper part of the digestive tract due to different gastric em ptying rates.