PHYSICOCHEMICAL CHARACTERISTICS OF EMULSIONS DURING FAT DIGESTION IN HUMAN STOMACH AND DUODENUM

Seven fasting subjects were fitted with nasogastric and nasoduodenal t ubes and received intragastrically a coarsely emulsified test meal. Ga stric and duodenal aspirates were collected after 1, 2, 3, and 4 h. In the duodenum, most lipids (>90%) were present as emulsified droplets 1-100 mu m in size. Large droplets and unemulsified material present i n the test meal (>100 mu m) disappeared, whereas smaller droplets (1-5 0 mu m) were generated after 1 h of digestion. Thus the median lipid d roplet diameter significantly decreased (19.6 vs. 56.5 mu m in the tes t meal) and the droplet surface area significantly increased (1.58 vs. 0.70 mu m(2)/g fat). Intermediate droplet diameters were 34.3, 46.3, and 27.6 mu m after 2, 3, and 4 h, respectively. In the stomach, a com parable emulsion particle size pattern was observed, with median dropl et diameters of 17.2, 37.9, 52.4, and 41.6 mu m after 1, 2, 3, and 4 h , respectively. However, the extent of triglyceride hydrolysis was muc h lower in the stomach (6-16%) than in the duodenum (42-45%), where sm all droplets were enriched in lipolytic products, cholesterol, and pho spholipids. The present findings show for the first time that most die tary lipids are present in the human duodenum as emulsified droplets 1 -50 um in size and that no further marked emulsification of dietary fa t occurs in the duodenum compared with the stomach.