Mechanisms underlying the desorption of long-chain lipolytic products by cyclodextrins: application to lipase kinetics in monolayer

Abstract

The desorption rates of monolayers of insoluble lipolytic products, oleic acid (OA) and mono-olein (MO), spread at the air-water interface, were measured in the presence of β-cyclodextrin (β-CD) or α-cyclodextrin (α-CD) at various subphase pH values. The desorption rates of the CD-OA complex at pH 2 can be satisfactorily described by a kinetic Langmuir equation revealing the existence of an energy barrier in the complex formation of the CD-OA. The dramatic increase observed in the desorption rates of the CD-OA complex at alkaline pH is in agreement with the theoretical prediction that a diffusion process is likely to occur from the surface to the bulk phase. Our results are consistent with the formation of hydrogen bonds between the ionized OA molecule and the O(6)H groups in the CD cavity. In the presence of β-CD in the subphase, comparable rates of hydrolysis of medium and long-chain monomolecular films of various glycerides by human pancreatic lipase (HPL) and Humicola lanuginosa lipase (HL) were observed. Comparisons between the above rates of enzymatic hydrolysis and the desorption rates of the CD-lipolytic product complexes indicated that the monomolecular film hydrolysis is rate limiting and does not depend on the type of CD used.