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Abstract
Glycerol-based galloyl esters, 1‐o‐galloylglycerol (GG) and 1,2-dipalmitoylgalloylglycerol (DPGG), were synthesized using enzymatic transesterification under solvent-free condition. An immobilized and commercially available food-grade Candida antarctica lipase B, Lipozyme® 435, was used as the biocatalyst. GG was synthesized through glycerolysis of propyl gallate (PG), while DPGG was produced from the transesterification of PG and tripalmitin. The structures of GG and DPGG were elucidated using Fourier-transform infrared spectroscopy (FT-IR), electrospray ionization high-resolution accurate-mass tandem mass spectrometry (ESI-HRAM-MS/MS), and nuclear magnetic resonance spectroscopy (NMR). At 70 °C, DPGG was obtained at a yield of 33.0 ± 2.0% with PG conversion at 44.8 ± 1.8% when the following conditions were used: 25 substrate molar ratio of tripalmitin to PG, 120 h reaction time, and 25% enzyme load relative to the total substrate weight. In the small-scale reaction, a 67.1 ± 1.9% GG yield was obtained at 50 °C, 25:1 (glycerol:PG) substrate molar ratio, 120 h reaction time, and 23.8% enzyme load. A higher GG yield (76.9 ± 1.2% ) was achieved in the scaled-up reaction. The antioxidant properties measured by the 1,1-diphenyl-2-picrylhydrazyl (DPPH•) and 2,2′-azinobis (3-ethylbenzthiazoline-6-sulfonic acid) (ABTS•+) assays, showed that GG and gallic acid (GA) exhibited greater scavenging capacities than PG (GG = GA>PG). From the results of the ferric reducing antioxidant power (FRAP) and hydrogen peroxide (H2O2) scavenging assays, GG exhibited the highest scavenging capacity (GG > GA > PG). In a structured lipid (SL) produced by the enzymatic acidolysis of menhaden oil with caprylic and stearic acids, GG, along with other phenolic compounds, including PG, GA, ferulic, caffeic, rosmarinic, and carnosic acids, tocopherols, and butylated hydroxytoluene (BHT) were investigated as antioxidants at the concentration of 100 ppm. SL with GG, rosmarinic acid, or BHT showed the highest oxidative stability during an accelerated oxidation test with the total oxidation (TOTOX) value of 250 after 18 d. Based on the oxidation induction time (OIT) determined using differential scanning calorimetry (DSC), a mixture of GG and tocopherols at 50:50 ppm had the strongest protective effect on SL (OIT = 115.1 min) compared to the other tested compounds or combinations at the same concentration (OIT < 100 min).