Vol. 69, Nr. 1, 2004—JOURNAL OF FOOD SCIENCE FEP1 Published on Web 12/05/2003 © 2004 Institute of Food Technologists Further reproduction without permission is prohibited Food Engineering and Physical Properties JFS: Food Engineering and Physical Properties Lipase-mediated Acidolysis of Fully Hydrogenated Soybean Oil with Conjugated Linoleic Acid J. ORTEGA, A. LÓPEZ-HERNANDEZ, H.S. GARCIA, AND C.G. HILL JR. ABSTRACT: Interesterification (acidolysis) of fully hydrogenated soybean oil (melting point = 69.9 °C) with conjugated linoleic acid (CLA) was carried out in a batch reactor at 75 °C. Lipases from Candida antarctica, Rhizomucor miehei, Pseudomonas sp., and Thermomyces lanuginosus were used at 5% (wt/wt) of the total substrate load. The lipase from Rhizomucor miehei produced the fastest reaction rates, and the greatest extent of incorporation of CLA residues in acylglycerols was achieved in 12 h. Lipases from C. antarctica and T. lanuginosus produced slower initial rates, and maximum extents of incorporation of CLA residues were achieved in 24 h. The lipase from Pseudomonas sp. produced the slowest initial rate. The corresponding maximum extent of incorporation was reached in 48 h. Differential scan- ning calorimetry analysis of the triacylglycerol (TAG) fractions produced by C. antarctica, R. miehei, and T. lanuginosus lipases after purification by solid phase extraction showed little variation in melting point (60.4 °C, 62.8 °C, and 60.1 °C, respectively). By contrast, the corresponding TAG fraction produced by the Pseudomonas sp. lipase melted at 48.4 °C. The positional distribution of the TAGs produced by the lipase from Pseudomonas sp. differed appreciably from those produced by the other enzymes. Keywords: soybean oil, linoleic acid, lipase, interesterification, acidolysis Introduction C onjugated linoleic acid (CLA) is a collective term that refers to a mixture of positional and geometric isomers of linoleic acid containing double bonds in the 8 and 10, 9 and 11, 10 and 12, or 11 and 13 positions, in either cis or trans configurations (Ha and others 1987; Pariza and others 1997). The richest natural sources of CLA are animal fats, especially milk fat and meat from ruminants (Chin and others 1992). It is known that these isomers are formed as inter- mediates during the biohydrogenation of linoleates by rumen bac- teria (Kepler and others 1966; Kelly and others 1998). Parodi (1977) 1st reported the cis-9, trans-11 isomer (now known as rumenic acid [Kramer and others 1998]) as the major component of CLA in bovine milk fat. The cis-9, trans-11, and trans-9, cis-11 isomers have been associated with important biological activities (Ha and others 1990; Ip and others 1991, 1994a, 1994b, 1994c; Shultz and others 1992a, 1992b; Parodi 1994, 1996), for example, enhancement of the im- mune system (Cook and others 1993; Miller and others 1994), and have been demonstrated to inhibit development of atherosclerosis in animals (Lee and others 1994). CLA may also act as a growth-pro- moting agent (Chin and others 1994), exert a hypocholesterolemic effect (Lee and others 1994), and play a role in mobilization of body fat (Delany and others 1999). Ip and others (1994b) have suggest- ed that relatively low consumption of CLA (3.5 g/d for a 70-kg per- son) would provide a protective anticarcinogenic effect. Conse- quently, CLA promises to be an important addition to the class of foods used as nutraceuticals. Preparation of structured lipids is currently attracting worldwide attention as a technology that uses enzymatic interesterification with lipases as a technique for modification of oils to improve their nutritional and health benefits. Enzyme catalyzed acidolysis is an approach to increasing the CLA content of fats (triacylglycerols [TAGs]) by interesterification. In acidolysis, a portion of the original fatty acid residues is replaced by CLA residues. Structured lipids may provide the most effective means of delivering CLA for nutri- tive or therapeutic purposes, and targeting specific diseases and metabolic conditions. For a simple physical mixture of 2 lipids, the rates at which the various constituents are absorbed after ingestion are those rates that are characteristic of the individual TAG. By con- trast, for structured lipids the different molecular compositions of the various TAGs (different positional distributions of fatty acid residues) may lead to significant differences in the rates of hydrol- ysis and absorption, resulting in different metabolic fates of the TAG (Lee and Akoh 1998). Structured lipids can also be synthesized for the purpose of improving or changing the physical and/or chemical characteristics of acylglycerols, for example, melting point, solid fat content, iodine value, and saponification number. Several reports of enzymatic interesterification of fats and oils with CLA are available in the literature. Garcia and others (1998, 1999, 2000b) have reported the feasibility of increasing the CLA content of butterfat, whereas In-Hwan and others (2001) have in- corporated CLA in tricaprylin. McNeill and others (1999) have inter- esterified CLA with palm oil TAG. Martinez and others (1999) have used CLA to interesterify corn oil in several organic solvents. Garcia and others (2000a) and Torres and others (2001) have studied in- corporation of CLA residues in fish oil. In principle, using an appro- priate enzyme, one can replace at least a significant fraction of the original fatty acid residues in a fat or oil with CLA residues. The altered composition of the TAGs comprising the interester- MS 20020245 Submitted 4/17/02, Revised 5/26/02, Accepted 9/27/03. Authors Ortega, López, and Garcia are with UNIDA—Instituto Tecnológico De Veracruz, M.A. de Quevedo 2779, Veracruz, Ver. 91897 Mexico. Authors Garcia and Hill are with Dept. of Chemical Engineering, Univ. of Wisconsin, 1415 Engineering Dr., Madison, WI 53706. Direct inquiries to author Garcia (E- mail: hsgar cia@itv er .edu.mx).