Approaches for the enzymatic synthesis of alkyl hydroxycinnamates and applications thereof.

Alkyl hydroxycinnamates (AHs) is a group of molecules of biotechnological interest due to their cosmetic, food, and pharmaceutical applications. Among their most interesting uses are as UV protectants, skin depigmentation agents, and antioxidant ingredients which are often claimed for their antitumoral potential. Nowadays, many sustainable enzymatic approaches using low-cost starting materials are available and interesting immobilization techniques are helping to increase the reuse of the biocatalysts, allowing the intensification of the processes and increasing AHs accessibility. Here a convenient summary of AHs most interesting biological activities and possible applications is presented. A deeper analysis of the art state to obtain AHs, focusing on most employed enzymatic synthesis approaches, their sustainability, acyl donors relevance, and most interesting enzyme immobilization strategies is provided.Key points• Most interesting alkyl hydroxycinnamates applications are summarized.• Enzymatic approaches to obtain alkyl hydroxycinnamates are critically discussed.• Outlook of enzyme immobilization strategies to attain alkyl hydroxycinnamates.

Carrier-bound and carrier-free immobilization of type A feruloyl esterase from Aspergillus niger: Searching for an operationally stable heterogeneous biocatalyst for the synthesis of butyl hydroxycinnamates.

Feruloyl esterases synthesize butyl hydroxycinnamates, molecules possessing interesting biological properties, nonetheless, they exhibit a low stability under synthesis conditions in organic solvents, restricting its use. To enhance its operational stability in synthesis, we immobilized type A feruloyl esterase from Aspergillus niger (AnFAEA) using several carrier-bound and carrier-free strategies. The most active biocatalysts were: 1) AnFAEA immobilized on epoxy-activated carriers (protein load of 0.6 mgenzyme x mg-1carrier) that recovered 91 % of the initial hydrolytic activity, and 2) AnFAEA aggregated and cross-linked in the presence of 5 mg of BSA and 15 mM of glutaraldehyde (AnFAEA-amino-CLEAs), which exhibited 385 % of its initial hydrolytic activity; both using 4-nitrophenyl butyrate as substrate. The AnFAEA-amino-CLEAs were 12.7 times more thermostable at 60 °C than the AnFAEA immobilized on epoxy-activated carrier, thus AnFAEA-amino-CLEAs were selected for further characterization. Interestingly, during methyl sinapate hydrolysis (pH 7.2 and 30 °C), AnFAEA-amino-CLEAs KM was 15 % higher, while during butyl sinapate synthesis the KM was reduced in 63 %, both compared with the soluble enzyme. The direct esterification of butyl sinapate at solvent free conditions using sinapic acid 50 mM, reached 95 % conversion after 24 h employing AnFAEA-amino-CLEAs, which could be used for 10 cycles without significant activity losses, demonstrating their outstanding operational stability.