Synthesis of liposoluble carboxylic acid ascorbyl esters catalyzed by immobilized lipases

• Main Author: Ćorović, Marija
• Other Authors: Bezbradica, Dejan, Knežević-Jugović, Zorica, Antov, Mirjana, Marinković, Aleksandar
• Format: Doctoral or Postdoctoral Thesis
• Language: unknown
• Published: Univerzitet u Beogradu, Tehnološko-metalurški fakultet 2016
• Subjects: vitamin C; carboxylic acids; lipases; esterification; liposolubility; antioxidant; optimization; immobilization; kinetics; karboksilne kiseline; lipaze; esterifikacija; liposolubilnost; antioksidans; optimizacija; imobilizacija; kinetika; Antarc*; Antarctica
• Online Access: http://TechnoRep.tmf.bg.ac.rs/handle/123456789/4632; http://eteze.bg.ac.rs/application/showtheses?thesesId=3484; https://fedorabg.bg.ac.rs/fedora/get/o:12130/bdef:Content/download; http://vbs.rs/scripts/cobiss?command=DISPLAY&base=70036&RID=48117775; http://TechnoRep.tmf.bg.ac.rs/bitstream/id/2158/4629.pdf; https://hdl.handle.net/21.15107/rcub_technorep_4632

In this thesis, possibility of efficient and economical production of carboxylic acid ascorbyl esters catalyzed by immobilized lipases was examined. Vast number of lipases, acyl donors, and organic solvents was tested. Suitable reaction mediums were polar organic solvents in which vitamin C was soluble (t-butanol and acetone). It was determined that lipase B from Candida antarctica (CAL B) was the most active catalyst in the esterification and that its affinity towards saturated short- and medium-chain carboxylic acids and unsaturated longchain fatty acids was higher comparing to saturated long-chain fatty acids. Antioxidant activity of these esters was higher, as well. Optimization of crucial reaction parameters was performed by using statistically designed experimental plan and response surface methodology for the synthesis of ascorbyl oleate. As a response, specific yield, which represents amount of ester produced per mass of utilized immobilized lipase, was chosen, since it gave insight in cost effectiveness of enzymatic process. In that way, at 60 °C, with 0.135 M of vitamin C, 0.2 %(w/v) of lipase, oleic acid in excess (8:1), and at initial water content of 0.018 %(v/v), maximum specific ester yield of 16.7 mmol g-1 was accomplished. Process efficiency was additionally enhanced by adding molecular sieves in order to remove excessive amount of water, by reusing biocatalyst in consecutive reaction cycles, and by reactivating partially inactivated lipase. Kinetic study revealed that initial reaction rates could be modeled by ping-pong bi-bi mechanism with inhibition by vitamin C. By including reverse reaction of hydrolysis in final model, experimental data at long reaction times were properly fitted, as well. Considering the fact that high price of commercial immobilized preparation (Novozym® 435) that was used is one of the largest obstacles for commercialization of the enzymecatalyzed ascorbyl ester synthesis processes, within subsequent part of dissertation different carriers and methods for the ...