Enzymatic Synthesis of Flavours and Fragrances, Antioxidants and Antimicrobials on the Example of Benzyl Alcohol and its Selected Derivatives

The "green" alternative to traditional chemical synthesis can be enzyme-based processes. Phenolic compounds are known to be biologically active substances but in many cases, their enzymatic modification by esterification or transesterification allows for obtaining esters with other, new features, like changed flavour properties, enhanced solubility in lipophilic media or enhanced antimicrobial activity. The aim of the work was the enzymatic synthesis of flavours and fragrances, antioxidants and antimicrobials with the use of benzyl alcohol, and its selected derivatives, namely 2-hydroxybenzyl, 4-hydroxybenzyl, 4-methoxybenzyl (anisyl), 4-hydroxy-3-methoxybenzyl (vanillyl), 4-nitrobenzyl, and 3,4-(methylenedioxy)benzyl (piperonyl) alcohols via transesterification with vinyl acetate. For obtaining the esters, Candida antarctica lipase B (10% w/w by the mass of substrates) was used and the reactions were performed in isooctane and 2 mmoles of chosen alcohol and vinyl acetate. The conversion yields of esters were dependent on the structure of alcohols and their solubility in the solvent and ranged from about 17% in the case of 4-hydroxybenzyl acetate to approximately 90% of benzyl acetate. The performed reactions allowed the creation of esters with fruity-sweet-floral odours, like benzyl acetate, 4-methoxybenzyl acetate and piperonyl acetate. Furthermore, vanillyl acetate has proven to be the best antioxidant in the DPPH· (2,2-diphenyl-1-picrylhydrazyl) assay, with the IC₅₀ value of 0.83 ± 0.04 mM. In the reference to antimicrobial activity, the disc diffusion method was applied and the following bacteria were used: Escherichia coli PCM 2057 and Staphylococcus aureus PCM 2054. The vast majority of synthesized esters were not effective against tested bacteria, but vanillyl acetate was able to moderately inhibit the growth of the microorganisms, and the largest inhibition zone diameters were obtained for 2-hydroxybenzyl acetate and the values obtained against E. coli were 19.0 ± 1.0 mm and 20.3 ± 0.6 in the case of S. aureus.