title: Enzymatic incorporation of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) into medium chain triacylglycerol oil (MCTO) and virgin coconut oil (VCO): positional distribution and oxidative stability of structured lipid products
Creators: name: Nguyen, Lanh Van
Publisher: name: Memorial University of Newfoundland
publisherIdentifier: https://ror.org/04haebc03
publisherIdentifierScheme: ROR
Year: 2024

description: The lipase-catalyzed acidolysis for producing structured lipids from medium-chain triacylglycerol oil (MCTO) and virgin coconut oil (VCO) with long-chain n-3 polyunsaturated fatty acids (n-3 PUFAs), specifically docosahexaenoic acid (DHA) and/or eicosapentaenoic acid (EPA) was investigated. Three commercial enzymes, namely Thermomyces lanuginosus lipase, Rhizomucor miehei lipase, and Candida rugosa lipase were used as biocatalysts. Among them, immobilized Lipozyme® TLIM from Thermomyces lanuginosus demonstrated the highest degree of DHA or EPA or DHA+EPA incorporation into both MCTO and VCO. The effects of varying reaction parameters, including the mole ratio of substrates, enzyme load, reaction time, and reaction temperature, were monitored to determine the most effective conditions. Incorporation of n-3 PUFAs into MCTO and VCO increased significantly (p<0.05) with increasing mole ratio of substrates. As the enzyme load increased from 1 to 4%, the incorporation of n-3 PUFAs also increased; however, it decreased when the enzyme load was further increased to 6%. The incorporation of these fatty acids increased with reaction time, from 12 to 36 h, but decreased at 48 h. Similarly, the incorporation of n-3 PUFAs increased with temperature from 35 to 45 oC and decreased at 55 and 65 oC. The highest incorporation of n-3 PUFAs was achieved at a mole ratio of 1:3 (MCTO or VCO to DHA or EPA). The maximum incorporation of DHA+EPA occurred at a mole ratio of 1:3:3 (MCTO or VCO to DHA+EPA). Response surface methodology (RSM) was employed to maximize the incorporation of n-3 PUFAs while minimizing enzyme usage. The process parameters studied included enzyme amount (2, 4, 6%), reaction temperature (35, 45, 55 oC), and reaction time (24, 36, 48 h). All experiments were carried out using a central composite design (CCD). Under optimal conditions of 3.3% Thermomyces lanuginosus enzyme, 42.22 oC, and 33.37 h, the incorporation of DHA was 45.0% in MCTO and 32.9% in VCO. Optimization of acidolysis with EPA resulted in a maximum EPA incorporation of 47.4% in MCTO and 44.5% in VCO. Similarly, the maximum incorporation of DHA+EPA was achieved with 50.4% in MCTO and 47.0% in VCO. Another study on stereospecific analysis was conducted to identify the positional distribution of fatty acids in the triacylglycerol (TAG) of n-3 PUFAs-enriched oils. In n-3 PUFAs-enriched MCTO, these n-3 PUFAs were predominantly esterified at the sn-1 and sn-3 positions, while C8:0 and C10:0 were mainly located at the sn-2 position. Similarly, in n-3 PUFAs-enriched VCO, these n-3 PUFAs were primarily attached to the sn-1 and sn-3 positions. C12:0 was mainly esterified at the sn-3 position, and C8:0 and C10:0 were distributed randomly across all three positions. The oxidative stability of enzymatically modified oils, as well as their unmodified counterparts, was evaluated under Schaal oven conditions at 60 oC over a 12-day storage period. The assessment involved measuring conjugated dienes (CD), 2-thiobarbituric acid reactive substances (TBARS), and headspace volatile compounds. Among the oils examined, the enzymatically modified products exhibited higher levels of CD and TBARS compared to their unmodified counterparts. Additionally, the modified oils showed a significantly increased (p<0.05) rate and extent of lipid peroxidation, as indicated by the rising of CD and TBARS values and the accumulation of volatile compounds over the storage period. The primary volatile compounds identified in the enzymatically modified oils included acetaldehyde, propanal, and acrolein, which were not present in the unmodified oils.