Published: August 10, 2011 r2011 American Chemical Society 9588 dx.doi.org/10.1021/jf201992k | J. Agric. Food Chem. 2011, 59, 9588–9595 ARTICLE pubs.acs.org/JAFC Characterization of Stearidonic Acid Soybean Oil Enriched with Palmitic Acid Produced by Solvent-free Enzymatic Interesterification Sarah A. Teichert and Casimir C. Akoh* Department of Food Science and Technology, The University of Georgia, Athens, Georgia 30602-2610, United States ABSTRACT: Stearidonic acid soybean oil (SDASO) is a plant source of n-3 polyunsaturated fatty acids (n-3 PUFAs). Solvent-free enzymatic interesterification was used to produce structured lipids (SLs) in a 1 L stir-batch reactor with a 1:2 substrate mole ratio of SDASO to tripalmitin, at 65 °C for 18 h. Two SLs were synthesized using immobilized lipases, Novozym 435 and Lipozyme TL IM. Free fatty acids (FFAs) were removed by short-path distillation. SLs were characterized by analyzing FFA and FA (total and positional) contents, iodine and saponification values, melting and crystallization profiles, tocopherols, and oxidative stability. The SLs contained 8.15 and 8.38% total stearidonic acid and 60.84 and 60.63% palmitic acid at the sn-2 position for Novozym 435 SL and Lipozyme TL IM SL, respectively. The SLs were less oxidatively stable than SDASO due to a decrease in tocopherol content after purification of the SLs. The saponification values of the SLs were slightly higher than that of the SDASO. The melting profiles of the SLs were similar, but crystallization profiles differed. The triacylglycerol (TAG) molecular species of the SLs were similar to each other, with tripalmitin being the major TAG. SDASO’s major TAG species comprised stearidonic and oleic acids or stearidonic, R- linolenic, and γ-linolenic acids. KEYWORDS: lipase, stearidonic acid soybean oil, structured lipid, tripalmitin ’ INTRODUCTION Stearidonic acid (SDA) soybean oil (SDASO) is a soybean oil that is enriched with SDA (C18:4n-3) consisting of approximately 20% stearidonic, 24% linoleic, and 12% palmitic acids. 1 SDA is an n-3 polyunsaturated fatty acid (n-3 PUFA). PUFAs are often found in plants, fungi, microalgae, and fish. Fish is the main source of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) but contains only small amounts of SDA. 2 The richest sources of SDA are algae and plants. EPA is a very long chain n-3 PUFA that inhibits platelet aggregation and lowers inflammation. James et al. 3 suggested that the daily ingestion of fish or fish oil to obtain the health benefits of n-3 PUFAs is not a sustainable long-term approach. However, increasing ingestion of plant-based sources of n-3 PUFAs is required to increase the tissue concentration of EPA and DHA. 3 SDA is the first metabolite of R-linolenic acid (ALA) in the metabolic pathway leading to EPA by desaturases and elongases. 4 However, this conversion from ALA to EPA is often poor because the initial Δ6 desaturase enzyme is rate limiting in humans. 5 The consumption of SDA, instead of ALA, would skip the rate-limiting step, allowing for better conversion to EPA. Therefore, development of plant-based sources of n-3 PUFAs could be a solution for the supply of these fatty acids in the future. Miles et al. 6 observed that neither SDA nor 20:4n-3 appeared in the peripheral blood mononuclear cell when dietary SDA was ingested at a level of 1.0 g/day, indicating that SDA was readily metabolized to EPA in the body. Dietary SDA was found to increase EPA concentrations by 3À4-fold more effectively than similar levels of ALA. 3,7 SDA was approximately one-third as effective as dietary EPA, 8 and the effectiveness of these FAs in increasing EPA concentrations in tissues is as follows: EPA > SDA > ALA. 3 James et al. 3 conducted a double-blind, parallel group study to examine the effect of dietary SDA on increasing tissue concentrations of EPA in humans and compared SDA’s ability with that of ALA and EPA. They concluded that SDA vegetable oils were more effective in increasing EPA tissue con- centrations than the currently used ALA vegetable oils. SDA has been noted as a possible potent inhibitor of cancer growth, inhibitor of platelet aggregation, anti-inflammatory pharmaceutical, and provider of cardiovascular benefits. 2 EPA has been linked to reductions in inflammation 9 and neurological disorders. 10 A previous study reported the tocopherol content of SDA soybean as 9.6 mg/100 g of R-tocopherol, 79.3 mg/100 g of γ-tocopherol, and 28.8 mg/100 g of δ-tocopherol. 1 Tocopherols are unsapo- nifiable materials that are well-known for their cardiovascular benefits and antioxidant capacity. The ratio of n-6/n-3 PUFA is important in the diet. However, the Western diet is high in n-6 FAs, often resulting in a ratio of 15:1À16.7:1. 11 The high ratio of n-6 FAs can result in increased risk of cardiovascular, inflammatory, and autoimmune diseases and cancer. Conversely, a lower n-6/n-3 PUFA ratio would suppress these negative effects. For example, a lower ratio of 2:1À3:1 suppressed inflammation in patients with rheumatoid arthritis, and a ratio of 5:1 had a beneficial effect on patients with asthma. However, a ratio of 10:1 n-6/n-3 PUFA had adverse consequences. 11 Premature infants often are limited in their ability to make EPA and DHA from ALA. 12 Structured lipids (SLs) are triacylglycerols (TAGs) that have been modified to change the FA composition and/or their position in the glycerol backbone by chemically and/or enzyma- tically catalyzed reactions. 13 SLs can be used in a wide variety of food applications such as margarines, shortenings, cookies, and salad dressings. Another possible application of SLs could be their use in infant formula as a human milk fat (HMF) analogue. Received: May 19, 2011 Revised: August 8, 2011 Accepted: August 10, 2011