| Summary: | Lipase-catalyzed esterification and transesterification reactions of selected phenolic acids with lipids were investigated in organic solvent media. The esterification of linoleyl alcohol with dihydrocaffeic acid (DHA) in neat hexane medium resulted in highest esterification yield (EY) of 17% when a Candida antarctica lipase (Novozym 435) was used to catalyze the reaction. The use of co-solvents t-butanol and 2-butanone with hexane resulted in a dramatic increase in EY. The highest EY of 83% was obtained in hexane:2-butanone mixture of 85:15 (v/v) using Novozym 435; however lower EY (40%) was obtained when a lipase from Rhizomucor meihei (Lipozyme IM 20) was used. Increasing the amount of the co-solvent 2-butanone in the hexane:2-butanone mixture to 75:25 (v/v) resulted in a lower EY of 75% with Novozym 435; using the same enzyme, the esterification of a more unsaturated alcohol, linolenyl alcohol, with DHCA in the hexane:2-butanone mixture of 75:25 (v/v) resulted in EY of 76% which was similar to that obtained with linoleyl alcohol as lipid substrate. The esterification of DHCA and ferulic acid with linolenyl alcohol in the hexane:2-butanone mixture of 65:35 (v/v) resulted in an EY of 58 and 16%, respectively. Both linoleyl and linolenyl alcohols demonstrated mass action effects with EY of 99% in DHCA: fatty alcohol ratio of 1:8. Using a molar ratio of 1:2, the transesterification reactions of DHCA with trilinolein (TLA) and trilinolenin (TLNA) in hexane:2-butanone mixture of 75:25 (v/v) resulted in total transesterification yields (TYs) of phenolic lipids of 66 and 62%, respectively. The TYs of phenolic monoacylglycerols was higher than that of phenolic diacylglycerols for both TLA and TLNA transesterification reactions. A lower molar ratio of DHCA to TLA of 1:4 resulted in a lower TY of 53%. Using a molar ratio of 1:2, the TY of TLA and TLNA with ferulic acid in hexane:2-butanone mixture of 65:35 (v/v) was 16 and 14%, respectively. An equal molar transesterification reaction of DHCA with flaxseed oil, in a hexane:2-butanone mixture of 75:25 (v/v), resulted in the production of only phenolic monoacylglycerols (19%); however, decreasing the molar ratio resulted in the production of both phenolic mono and diacylglycerols. A molar ratio of DHCA to flaxseed oil (1:8) resulted in a TY of 76%, with 43 and 33% phenolic mono and diacylglycerols, respectively. Changing the solvent mixture of hexane:2-butanone from 65:35 to 85:15 (v/v) resulted in an increased in the TY of phenolic diacylglycerols from 24 to 55% with no significant effect on the TY of phenolic monoacylglycerols. The transesterification reaction resulted in a change in the composition of the C18:3 FA from 53% in the unmodified oil to 60 and 65% in the phenolic mono and diacylglycerols. Transesterification reaction of DHCA with fish liver oil in the solvent mixtures of hexane:2-butanone of 75:25 and 85:15 (v/v) resulted in TY of 56 and 65%, respectively. Transesterification in solvent: mixture of 75:25 resulted in a 40 and 16% TY of phenolic mono and diacylglycerols, respectively, whereas that in the solvent mixture of 85:15 (v/v) resulted in a 38 and 37% TY of phenolic mono and diacylglycerols, respectively. The structures of phenolic lipids of linoleyl and linolenyl alcohols with DHCA were confirmed by LC/MS analysis likewise for the phenolic mono and diacylglycerols from transesterification of DHCA with TLA and TLNA as well as flaxseed and fish liver oils. The phenolic esters of the fatty alcohols demonstrated radical scavenging properties similar to that of alpha-tocopherol but less than for DHCA; however, the phenolic lipids obtained with the use of TLA and TLNA as substrate as well as flaxseed and fish liver oil, demonstrated significant radical scavenging effects but less than that of alpha-tocopherol and DHCA.
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