Biosynthesis of ethyl esters of short-chain fatty acids using whole-cell lipase from Rhizopus chinesis CCTCC M201021 in non-aqueous phase

Abstract

A fungal strain capable of synthesizing ethyl esters of short-chain fatty acids was isolated from leaven (mouldy grains) samples through combined screening strategy of lipolysis and with esterification ability and was identified to be Rhizopus chinesis CCTCC M201021. When compared with other 10 commercial lipases, the whole-cell lipase of R. chinesis CCTCC M201021 (RCL) showed much higher ability in the synthesis of ethyl hexanoate during the screening of suitable lipases with a maximum yield of 96.5% after 72 h conversion using 0.5 M equal molar substrate concentration. Thereafter, the effect of important reaction parameters for enhancing ester formation by whole-cell RCL was investigated in this study. Higher esterification (>90%) was observed and maintained under chain length of carboxylic acids (C 2–C 8). Solvents with log P ( P: partition coefficient) >2.0 enhanced RCL activity to give high conversion (>88.8%). Effect of temperature on reaction showed better esterification at 30–40 °C. Increase in concentration of substrates (ethanol and acid) from 0.2 to 1.4 M led to decrease in molar conversion from 96 to 85% in the synthesis of ethyl hexanoate. Changing the molar ratio of acid/ethanol from 1:1 to 1:3 at 0.6 M acid concentration resulted in a maximal conversion of 98.5% at the ratio of 1:1.3. It was observed that better esterification could be achieved with initial water activity ( a w) ranging from 0.66 to 0.97. A crucial enzyme concentration of 6 g/l was chosen for research after effect on esterification reaction was examined. The half-life period of esterification for different flavor ester production indicated that whole-cell RCL was more stable in batch esterification reaction within 840–975 h of half-life period for ethyl flavor esters.