Structured lipids (SLs) containing palmitic, oleic, stearic, and linoleic acids, resembling human milk fat (HMF), were synthesized by enzymatic acidolysis reactions between tripalmitin, hazelnut oil fatty acids, and stearic acid. Commercially immobilized sn-1,3-specific lipase, Lipozyme RM IM, obtained from Rhizomucor miehei was used as the biocatalyst for the enzymatic acidolysis reactions. The effects of substrate molar ratio, reaction temperature, and reaction time on the incorporation of stearic and oleic acids were investigated. The acidolysis reactions were performed by incubating 1:1.5:0.5, 1:3:0.75, 1:6:1, 1:9:1.25, and 1:12:1.5 substrate molar ratios of tripalmitin/hazelnut oil fatty acids/stearic acid in 3 mL of n-hexane at 55, 60, and 65 degrees C using 10% (total weight of substrates) of Lipozyme RM IM for 3, 6, 12, and 24 h. The fatty acid composition of reaction products was analyzed by gas-liquid chromatography (GLC). The fatty acids at the sn-2 position were identified after pancreatic lipase hydrolysis and GLC analysis. The results showed that the highest C18:1 incorporation (47.1%) and highest C18:1/C16:0 ratio were obtained at 65 degrees C and 24 h of incubation with the highest substrate molar ratio of 1:12:1.5. The highest incorporation of stearic acid was achieved at a 1:3:0.75 substrate molar ratio at 60 degrees C and 24 h. For both oleic and stearic acids, the incorporation level increased with reaction time. The SLs produced in this study have potential use in infant formulas.

Structured lipids resembling human milk fat and containing GLA were synthesized by an enzymatic interesterification between tripalmitin, hazelnut oil FA, and GLA in n-hexane. Commercially immobilized 1,3-specific lipases, Lipozyme ® RM IM and Lipozyme ® TL IM, were used as the biocatalysts. The effect of these enzymes on the incorporation levels was investigated. A central composite design with five levels and three factors-substrate ratio, reaction temperature, and time-were used to model and optimize the reaction conditions via response surface methodology. Good quadratic models were obtained for the incorporation of GLA (response 1) and oleic acid (response 2) by multiple regression and backward elimination. The determination coefficient (R 2 ) values for the models were found to be 0.92 and 0.94 for the reactions catalyzed by Lipozyme RM IM, and 0.92 and 0.88 for the reactions catalyzed by Lipozyme TL IM, respectively. The optimal conditions generated from the models for the targeted GLA (10%) and oleic acid (45%) incorporation were 14.8 mol/mol, 55°C, and 24 h; 14 mol/mol, 55°C, and 24 h for substrate ratio (moles total FA/mol tripalmitin), temperature and time for the reactions catalyzed by Lipozyme RM IM and Lipozyme TL IM, respectively. Human milk fat substitutes containing GLA that can be included in infant formulas were successfully produced using both Lipozyme RM IM and Lipozyme TL IM enzymes. The effect of the two enzymes on the incorporation of GLA and oleic acid were found to be similar.Paper no. J11063 in JAOCS 82, 549-557 (August 2005).KEY WORDS: Enzymatic interesterification, GLA, hazelnut oil, human milk fat substitutes, response surface methodology, sn-1,3-specific lipase.Breast milk is the main and most preferred source of nutrients for infants, and human milk fat (HMF) is the component that supplies the highest fraction of the infant's required dietary energy. Human milks are characterized by the dominance of TAG (98% of HMF) in which the saturated 16-carbon palmitic acid (16:0) (20-30%) is in the sn-2 position (70%) of the glycerol backbone, the sn-1 and sn-3 positions being taken by unsaturated FA (1,2). Structured lipids (SL) resembling TAG of HMF can be produced by interesterification, using sn-1,3-specific lipases as biocatalysts, and such TAG can be used in infant food formulations (3,4). Numerous studies have been conducted on the production of HMF substitutes (5-9). There has also been a great interest in the supplementation of infant formulas with FA such as GLA, arachidonic acid (AA), EPA, and DHA.In infant formulas, GLA-containing oil, especially borage oil, is used for its health benefits and for its antagonist action on AA metabolism (10,11). Since GLA is rapidly elongated to di-homo-γ-linolenic acid and subsequently ∆5-desaturated to AA and since GLA is also cheaper and easier to produce than AA, an alternative and suggested way of supplementing infant formulas with AA is to use GLA instead of highly active AA (12)(13)(14). The amount of GLA in infant formulas prepared by physic...

Structured lipids resembling human milk fat (HMF) enriched with omega-3 fatty acids were synthesized by enzymatic acidolysis reactions between tripalmitin, hazelnut oil fatty acids (FA), and omega-3 FA concentrate. Response surface methodology was used to model and optimize the incorporation of omega-3 FA and oleic acid into tripalmitin, in hexane, using immobilized sn-1,3-specific lipase, Lipozyme RM IM. The three factors chosen were substrate molar ratio, reaction temperature, and reaction time. Good quadratic models were obtained for the incorporation of eicosapentaenoic acid (EPA) plus docosahexaenoic acid (DHA) (response 1) and oleic acid (response 2) by multiple regression and backward elimination. The determination coefficient (R2) value for the models was 0.95. The adjusted R2 values were 0.91 and 0.92 for responses 1 and 2, respectively. The optimal conditions generated from the models for the targeted total EPA and DHA (5%) and oleic acid (40%) incorporation were 12.4 mol/mol, 55 degrees C, and 24 h for substrate ratio, temperature, and time, respectively. The model was verified, which led to the production of a HMF ingredient with 76.6% palmitic acid at the sn-2 position.