In a first set of experiments, it was examined if, with four selected medium-chain fatty acids (MCFAs) (C6:0-C12:0) containing fat sources (coconut, MCTAG1, MCTAG2, butter) and six lipases, under gastric simulated conditions (pH 3 to 6, 3 h incubation, 37degreesC, with complex substrate), appropriate amounts of MCFAs could be liberated, which could provide a valuable alternative for nutritional antibiotics used in piglet nutrition. Depending on the conditions applied, up to 20% of the MCFAs could be enzymatically released into the medium. In a second set of experiments, the generation and antimicrobial effects of MCFAs from three selected MCFA-containing fat sources (coconut, MCTAG1 and MCTAG2) and one appropriate microbial lipase, applied under different combinations and concentrations, were studied. A minimal concentration of 0.35 g per 100 g incubation fluid or 0.025 M MCFAs in the medium (e.g., stomach, proximal gut) appears to be necessary to obtain a significant ( > 10-fold) suppression of the flora. This amount can be obtained by choosing an appropriate combination of sources and doses of fat and lipases. The in vitro protocol used offers an excellent tool for the screening of the numerous combinations of MCFA-containing fat sources and lipolytic enzymes for their usefulness as feed supplements which comply with the above conditions, which are generally accepted as the prerequisite for obtaining growth promotion. (C) 2002 Elsevier Science B.V. All rights reserved.
