DIGESTION AND ABSORPTION OF TUBE-FEEDING EMULSIONS WITH DIFFERENT DROPLET SIZES AND COMPOSITIONS IN THE RAT

Assimilation of lipid nutrients depends on the efficiency of emulsifie d fat hydrolysis by digestive lipases. As shown in vitro, the activity of preduodenal and pancreatic lipases is governed by the physicochemi cal properties of emulsions. Thus the aim of this study was to evaluat e in the rat how emulsions are digested and assimilated depending on t heir droplet size or solute composition. Fasted rats were intragastric ally tube fed emulsions with different median droplet sizes (0.6 mu m, fine; 22 mu m, coarse) or solute composition (0.8 mu m, complex fine) containing C-14-triolein and H-3-cholesterol. Two and 5 hours after f eeding, fat-droplet size was measured in gastric and duodenal contents , and lipids were radioactively quantified in different compartments. In the stomach, the droplet size of the fine emulsions significantly i ncreased to values (13 mu m to 24 mu m) comparable with those of the c oarse emulsion (35 mu mto 36 mu m) In the duodenum, the droplet sizes of the three emulsions were in the range of 14 mu m to 33 mu m. After 2 hours, gastric triglyceride hydrolysis was significantly higher with the fine than with the coarse emulsion and was lower with the complex fine emulsion. Gastric emptying of fat was significantly different, w ith the following decreasing order: coarse, fine, and complex fine emu lsion. In the small intestine, the fine and coarse emulsions were proc essed comparably, whereas the assimilation of the line complex emulsio n was significantly delayed. Calculations indicate that ingested fatty acids were distributed in the peripheral tissues at different rates w ith the same decreasing order. The fate of a lipophilic nutrient, chol esterol, was also markedly altered by the type of emulsion. These data support the concept that tube-fed emulsions with different droplet si zes and solute composition are digested differently and thus are metab olized differently.