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    Comparison of the performance of entrapped and covalently immobilized lipase in the synthesis of pear flavor
    (Walter De Gruyter Gmbh, 2017) Ozyilmaz, Gul; Yagiz, Esra
    Introduction: Although aroma esters are produced mostly by a chemical method that requires the use of aggressive chemical catalysts, enzymatic esterification has been very favored during previous two decades. The main aim of this study was to investigate the commercially important pear flavor, hexyl acetate (HAc), by the catalysis of immobilized lipase samples and to optimize the immobilization and operational conditions in detail. Methods: Lipases from Candida rugosa (CRL) and porcine pancreas (PPL) were immobilized using biodegradable polysaccharides, by entrapment in calcium alginate/chitosan composite gel (CRLCa-Alg/Chi and PPLCa-Alg/Chi) and by covalent binding onto the chitosan (CRLChi and PPLChi) carrier. Results: Among the several organic media, the highest esterification activites were observed in heptane. HAc yield decreased when substrate concentrations were higher than 50 or 75 mM. Yield increased with increase in reaction time up to the 5th hour in the batch type reactor while it increased during the 8 h reaction time for fixed bed reactors with lower yields. Discussion and conclusions: As well as synthesis conditions, immobilization parameters also affected HAc productivity. The amount of water in the microenvironment of lipase is so important not only for gaining its active conformation but only for the reaction direction.
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    Isoamylacetate production by entrapped and covalently bound Candida rugosa and porcine pancreatic lipases
    (Elsevier Sci Ltd, 2012) Ozyilmaz, Gul; Yagiz, Esra
    Candida rugosa lipase (CRL) and porcine pancreatic lipase (PPL) were immobilised by entrapping and also by covalent binding for use in synthesis of isoamyl acetate (IAAc), which has a typical banana flavour. Lipase entrapment was carried out by dripping sodium alginate (Na-Alg)-chitosan (Chi)-lipase mixture into CaCl2-glutaraldehyde (GAL) solution to obtain Ca-Alg/Chi(CRL/PPL). Immobilisation conditions were optimised as 1.5% Na-Alg, 1.5% chitosan and 0.15% GAL Ca-Alg/Chi(CRL/PPL) samples showed the highest activity when they were dried upon reaching 27% of their initial weights. Covalent binding was achived with Chi modified with spacerarm via glutaraldehyde to get Chi(CRL/PPL). The highest IAAc production was observed when 1,3-diaminopropane was used as a spacer arm. The best ester yield was achieved in heptane, at 40 and 45 degrees C reaction temperatures, 50 mM IAA and 50 or 75 mM AA concentrations. The amount of IAAc was nearly 10 times higher for the batch type than for the continuous packed bed column reactor. (C) 2012 Elsevier Ltd. All rights reserved.