Effects of Emulsifier
Charge and Concentration on
Pancreatic Lipolysis. 1. In the Absence of Bile Salts
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Abstract
An in vitro study is performed with sunflower oil-in-water
emulsions
to 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. For
all systems, three regions are observed when surfactant concentration
is scaled with the critical micelle concentration, <i>C</i><sub>S</sub>/cmc: (1) At <i>C</i><sub>S</sub> < cmc,
α ≈ 0.5 after 30 min and increases up to 0.9 after 4
h. (2) At <i>C</i><sub>S</sub> ≈ 3 × cmc, α
≈ 0.15 after 30 min and increases steeply up to 0.9 after 2
h for the cationic and nonionic surfactants, whereas it remains around
0.2 for the anionic surfactants. (3) At <i>C</i><sub>S</sub> above certain threshold value, α = 0 for all studied surfactants,
for reaction time up to 8 h. Additional experiments show that the
lipase hydrolyzes molecularly soluble substrate (tributirin) at <i>C</i><sub>S</sub> ≫ cmc, which is a proof that these
surfactants do not denature or block the enzyme active center. Thus,
we conclude that the mechanism of enzyme inhibition by these surfactants
is the formation of a dense adsorption layer on an oil drop surface,
which displaces the lipase from direct contact with the triglycerides