Effects of EmulsifierCharge and Concentration onPancreatic Lipolysis. 1. In the Absence of Bile Salts.

An in vitro study is performed with sunflower oil-in-wateremulsionsto clarify the effects of type of used emulsifier, its concentration,and reaction time on the degree of oil lipolysis, α. Anionic,nonionic, and cationic surfactants are studied as emulsifiers. Forall systems, three regions are observed when surfactant concentrationis scaled with the critical micelle concentration, CS/cmc: (1) At CS< cmc,α ≈ 0.5 after 30 min and increases up to 0.9 after 4h. (2) At CS≈ 3 × cmc, α≈ 0.15 after 30 min and increases steeply up to 0.9 after 2h for the cationic and nonionic surfactants, whereas it remains around0.2 for the anionic surfactants. (3) At CSabove certain threshold value, α = 0 for all studied surfactants,for reaction time up to 8 h. Additional experiments show that thelipase hydrolyzes molecularly soluble substrate (tributirin) at CS≫ cmc, which is a proof that thesesurfactants do not denature or block the enzyme active center. Thus,we conclude that the mechanism of enzyme inhibition by these surfactantsis the formation of a dense adsorption layer on an oil drop surface,which displaces the lipase from direct contact with the triglycerides. [ABSTRACT FROM AUTHOR]