Lipase-Catalyzed Synthesis Of Phenolic Lipids In Solvent-Free Medium Using Selected Edible Oils And Phenolic Acids.

摘要

The enzymatic synthesis of phenolic lipids (PLs) in solvent-free medium (SFM), by transesterification of flaxseed and fish liver oils with selected phenolic acids was investigated, using Candida antarctica lipase as the biocatalyst. The enzymatic synthesis of phenolic lipids from flaxseed oil was optimized in terms of water activity, agitation speed, enzyme and phenolic acid concentrations. Increasing the water activity of the flaxseed oil reaction mixture from 0.18 to 0.38 resulted in a significant increase in the bioconversion yield from 62 to 77%. The highest enzymatic activity (178 nmol of PLs/g solid enzyme/min) was obtained with the use of 40 mg of solid enzyme (400 PLU)/mL reaction volume at 150 rpm. Under the optimized conditions there was a significant increase in the proportion of linolenic acid (C18:3 n-3), which increased from 57% in the flaxseed oil to 75 and 64% in the produced phenolic mono- and diacylglycerols, respectively. The volumetric productivity (Pv) of the transesterification of flaxseed oil and 3,4-dihydroxyphenyl acetic acid (DHPA) in SFM was increased 11-fold as compared to that in organic solvent medium. On the other hand, a bioconversion yield of 61% was obtained for the transesterification of fish liver oil with dihydrocaffeic acid (DHCA). Optimization of the enzymatic synthesis of phenolic lipids in SFM from fish liver oil was carried out, using response surface methodology (RSM), based on a four-factor-five-level central composite rotatable design (CCRD). The optimal conditions for the enzymatic reaction were obtained at 50.0ºC, 20.9 mM phenolic acid, 51.2 mg of solid enzyme (512 PLU)/mL, 160 rpm agitation speed, water activity of 0.5 and 3.45 mg Silica gel/mL. The bioconversion yield obtained under these optimized conditions was 86.5%, which is very close to the predicted value of 84.5%. Hence, the predicted values showed good validation with the experimental ones. The overall results demonstrated that RSM can be applied effectively to optimize lipase-catalyzed synthesis of phenolic lipids in SFM, from fish liver oil and DHCA. Under the optimized conditions, there was a significant increase in the relative proportions of the two highly desirable essential fatty acids, where (EPA, C20:5 n-3) was increased from 11.5% in the unmodified fish liver oil to 21.2, 20.7, 20.8, 20.1 and 19.8% in dihydrocaffeoylated, 3,4-dihydroxyphenyl acetoylated, caffeoylated, feruloylated and sinapoylated lipids, respectively, whereas (DHA, C22:6 n-3) increased from 12.0% to 21.4, 19.4, 27.5, 22.1 and 22.0%, respectively. Atmospheric pressure chemical ionization-mass spectrophotometry (APCI-MS) analyses confirmed the formation of six 3,4-dihydroxyphenyl acetoylated and six dihydrocaffeoylated lipids from the transesterification of flaxseed and fish liver oils in SFM using DHPA and DHCA, respectively, as substrates. Although the synthesized phenolic lipids demonstrated radical scavenging activity, expressed as IC 50 from 1.6 to 3.7-fold higher than that of its corresponding phenolic acid, it was compared to that of alpha-tocopherol.