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The effects of important reaction parameters for enhancing flavour esters formation through lipase-catalyzed reaction were investigated in this study.Various commercial immobilized lipases were used to catalyze the esterification reaction between short-chain fatty acids and alcohols to produce flavour esters which are nonyl caprylate and ethyl valerate which differ in chain length of esters. These synthetic flavour esters with fruity notes are widely used in food, cosmetic and pharmaceutical industries. The effect of various reaction parameters was optimized to obtain a high yield of flavour esters. A maximum percentage for nonyl caprylate with conversion of flavour esters more than 90 % in a solvent-free system was successfully obtained under the following conditions: reaction time (RT), 5 hours; reaction temperature, 40 °C; amount of immobilized lipase, 25 % w/w of total substrate and shaking speed 200 rpm. Compared to ethyl valerate, a maximum percentage conversion of flavour ester more than 80 % in solvent free system was successfully obtained under following conditions: reaction time (RT), 45 minutes; reaction temperature, 40 °C; amount of immobilized lipase, 15 % w/w of total substrate and shaking speed 200 rpm. Comparison between these two ester showed that the chain length give an effect to optimize the reaction condition in esterification reaction.

Enzymatic synthesis of kojic ester, a bio-based whitening agent, was successfully carried out via esterification reaction between oleic acid and kojic acid. Commercial immobilized lipases of Novozym 435 and Lipozyme RM IM were used in combination as biocatalyst in the reaction system. Various reaction parameters were chosen to optimize the reaction in order to obtain a high yield of kojic ester including the best ratio of lipases, reaction time and reaction temperature. The optimum conditions for the synthesis of kojic ester was achieved at reaction time of 12 hours, temperature of 60 οC and equal ratio of lipases to produce more than 70 % yield. Antimicrobial tests of synthesized kojic ester towards several types of bacteria via Minimum inhibitory concentration (MIC) and Minimum bactericidal concentration (MBC) analyses were also examined. The results obtained suggested that kojic ester exhibits a good bactericidal effect towards all bacteria tested such as Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Salmonella typhimurium.

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