ENZYMATIC INTERESTERIFICATION OF TRIOLEIN WITH TRIPALMITIN IN CANOLA LECITHIN-HEXANE REVERSE MICELLES

Lipase-catalyzed interesterification of tripalmitin with triolein in c anola lecithin-hexane reverse micelles allowed for the successful modi fication of triolein and tripalmitin to yield a fat of intermediate pr operties between the two initial substrates. Acetone-insoluble canola lecithin (AIL) reverse micelles containing Rhizopus arrhizus lipase in buffer, or plain 0.1 M sodium phosphate buffer of pH 7.0, formed read ily in hexane. Both had an average Stokes' radius of approximately 40 angstrom, as determined by quasielastic light-scattering determination s. The reverse micelle system was stable and did not form higher-order micelle oligomers or aggregates. Biotransformation of the triglycerid es was performed at 47-degrees-C in a 50-mM AIL-hexane reverse micelle system containing 50% (w/w) oil at a water-to-surfactant ratio (w(o)) of 5.5. Dynamic (oscillatory) mechanical analysis indicated that the crystallization temperature of the fat dropped from 47.7 to 37.5-degre es-C as judged by the storage (G') and loss (G'') modulus vs. temperat ure profiles after 48 h of reaction. Differential scanning calorimetri c studies showed that the melting point of the fat dropped from 61 to 57-degrees-C after 48 h of reaction. Triglyceride analysis of the fat mixture by gas-liquid chromatography (GLC) indicated that, after 48 h of reaction, the tripalmitin content dropped from 34.5 to 29% (w/w), t he triolein content dropped from 64.5 to 52.1% (w/w) and the 1-oleyl-2 ,3-dipalmitin content reached 7.5% (w/w) while the 1-palmitoyl-2,3-dio lein content reached 7.2% (w/w). 1,2-Dipalmitoyldiglyceride and 1,2-di oleyldiglyceride contents reached 1.6 and 2.4% (w/w), respectively, af ter 48 h. Free fatty acid analysis of the fat mixture by GLC revealed that the free palmitic acid content increased from 0.28 to 2.4% (w/w) while the free oleic acid content increased from 1.4 to 5.4% (w/w) in the initial 24 h, after which the levels remained constant. The relati vely high initial free fatty acid content of the mixture was due to fr ee fatty acids present in the canola lecithin and not in the oils. Thi s enzymatic interesterification protocol utilizes, for the first time, an organic solvent commonly used in food processing operations and a food-grade and inexpensive surfactant that readily forms reverse micel les and yields a modified fat with improved rheological properties for use as an edible plastic fat.