Lipase-catalyzed interesterification of tripalmitin with triolein in canola lecithin-hexane reverse micelles allowed for the successful modification of triolein and tripalmitin to yield a fat of intermediate properties 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 readily in hexane. Both had an average Stokes' radius of approximately 40 angstrom, as determined by quasielastic light-scattering determinations. The reverse micelle system was stable and did not form higher-order micelle oligomers or aggregates. Biotransformation of the triglycerides 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-degrees-C as judged by the storage (G') and loss (G'') modulus vs. temperature profiles after 48 h of reaction. Differential scanning calorimetric 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), the 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-diolein content reached 7.2% (w/w). 1,2-Dipalmitoyldiglyceride and 1,2-dioleyldiglyceride contents reached 1.6 and 2.4% (w/w), respectively, after 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 relatively high initial free fatty acid content of the mixture was due to free fatty acids present in the canola lecithin and not in the oils. This 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 micelles and yields a modified fat with improved rheological properties for use as an edible plastic fat.
