The production of liquid crystalline product phases by pancreatic lipase in the absence of bile salts. A freeze-fracture study.
The hydrolysis of gum arabic-stabilized trioleylglycerol emulsions by pancreatic lipase was examined by freeze-fracture electron microscopy in the absence of bile salts. A sequence of liquid crystalline product phases was produced during the non-equilibrium conditions of hydrolysis. The morphology of the product phases were pH- and droplet size-dependent. At pH 8.3 the initial product phase was composed of homogeneous spherical vesicles regardless of trioleylglycerol drop size. As the reaction progressed the partially hydrolyzed droplets showed a crystalline 'crust' and a true lamellar phase which was often swollen, giving an isotropic appearance to this phase. Some droplets demonstrated a possible transitory hexagonal phase composed of tubular-lamellar elements in close association with the oil phase. These tubular-lamellar elements graded into a lamellar phase at the aqueous/product interface. A cubic phase was not discernible. At pH 7.0 a single phase was seen which covered the drop surface with an amorphous layered 'crust'. The significance of these phases is discussed in relation to those produced by pure and mixed lipids under equilibrium conditions.
D000818:Animals; D001647:Bile Acids and Salts; D003460:Crystallization; D005614:Freeze Fracturing; D006868:Hydrolysis; D008049:Lipase / Q000502:physiology*; D050356:Lipid Metabolism; D008066:Lipolysis; D010179:Pancreas / Q000201:enzymology*; D012995:Solubility; D013552:Swine; D014280:Triglycerides / Q000302:isolation & purification
D001647:Bile Acids and Salts; D014280:Triglycerides; D008049:Lipase