Encimska sinteza laktatnih estrov v nekonvencionalnih topilih - Kavčič, Sabina (S. Kavčič, 2014)
Laktatni estri, ki se pogosto uporabljajo v prehrambeni, farmacevtski in kozmetični industriji, so med najbolj pomembnimi derivati mlečne kisline. V današnjem času je velik poudarek na biorazgradljivosti produktov in uporabi okolju prijazne tehnologije, zato je potrebno temu primerno tudi izbrati topila za sintezo laktatnih estrov. Encimsko katalizirane reakcije lahko namesto v vodnem mediju izvajamo tudi v konvencionalnih organskih topilih ali v nekonvencionalnih topilih, kot so superkritični fluidi in ionske tekočine. Namen doktorske disertacije je bil izvesti encimsko sintezo laktatnih estrov, natančneje n-butil laktata, v nekonvencionalnih topilih. Kot nekonvencionalna topila smo uporabili superkritične fluide (superkritični ogljikov dioksid, superkritični trifluorometan in superkritični etan) in ionsko tekočino (CYPHOS IL-201). Vsa uporabljena topila predstavljajo zanimiv razred topil za encimsko katalizirane reakcije. Imobilizirano lipazo B iz Candida antarctice smo uspešno uporabili kot biokatalizator za encimsko katalizirano esterifikacijo D,L-mlečne kisline z n-butanolom v visokotlačnem mešalnem šaržnem reaktorju. V superkritičnem ogljikovem dioksidu smo proučili vpliv razmerja substratov (D,L-mlečna kislina:n-butanol), koncentracije molekularnih sit, hitrosti mešanja, večkratne uporabe encima, tlaka, temperature in koncentracije ko-topila (n-heksan) na izkoristek D,L-mlečne kisline, produktivnost in začetno hitrost tvorbe estra n-butil laktata. Prav tako smo optimirali reakcijske parametre, tlak, temperaturo in koncentracijo ko-topila (n-heksan), pri izvedbi encimske esterifikacije v superkritičnem trifluorometanu. V sistemu superkritični ogljikov dioksid/ionska tekočina in superkritični trifluorometan/ionska tekočina pa smo proučili vpliv koncentracije ionske tekočine CYPHOS IL-201, temperature, tlaka in koncentracije encima na potek reakcije. Nadalje smo očistili encimsko sintetiziran n-butil laktat ter določili antimikrobno aktivnost na različne testne mikroorganizme (Saccharomyces cerevisiae, Aspergillus niger, Trichoderma viride, Penicillium cyclopium, Escherichia coli, Pseudomonas fluorescens in Bacillus cereus). Lactic acid esters, which are widely used in the food, pharmaceutical and cosmetics industries are among the most important derivatives of lactic acid. Nowadays the biodegradability of the products and the use of environment-friendly technologies are of great importance, therefore a appropriate solvent for the synthesis of lactate esters should be choosen. In stead of aqueous medium, enzyme catalyzed reactions could be performed in conventional organic solvents or in nonconventional solvents, such as supercritical fluids and ionic liquids. The purpose of the dissertation was to carry out the enzymatic synthesis of lactate esters, specifically n-butyl lactate in nonconventional solvents. As the nonconventional solvents, the supercritical fluids (supercritical carbon dioxide, supercritical trifluoromethane and supercritical ethane) and ionic liquid (CYPHOS IL-201) were used. All used solvents present an interesting class of solvents for enzyme-catalyzed reactions. The immobilized lipase B from Candida antarctica was successfully used as a biocatalyst for the enzyme-catalyzed esterification of D,L-lactic acid with n-butanol in a high-pressure batch stirred-tank reactor. The influence of substrates ratio (D,L-lactic acid:n-butanol), concentration of molecular sieves, stirring rate, multiple use of the enzyme, pressure, temperature and concentration of co-solvent (n-hexane) on the efficiency of D,L-lactic acid, yield (productivity) and the initial rate of formation of the n-butyl lactate ester was studied when the reaction was performed in supercritical carbon dioxide. Also, the reaction parameters, such as, pressure, temperature and concentration of co-solvent (n-hexane) were optimized when the enzymatic esterification was carried out in the supercritical trifluoromethane. In the systems supercritical carbon dioxide/ionic liquid and supercritical trifluoromethane/ionic liquid, the impact of the concentration of ionic liquids CYPHOS IL-201, temperature, pressure and concentration of the enzyme of the reaction were studied. Furthermore, the antimicrobial activity of enzyme synthesized n-butyl lactate against a variety of test microorganisms (Saccharomyces cerevisiae, Aspergillus niger, Trichoderma viride, Penicillium cyclopium, Escherichia coli, Pseudomonas fluorescens and Bacillus cereus) was determined.