Jingcan Sun

Optimisation of flavour ester biosynthesis in an aqueous system of coconut cream and fusel oil catalysed by lipase.

Coconut cream and fusel oil, two low-cost natural substances, were used as starting materials for the biosynthesis of flavour-active octanoic acid esters (ethyl-, butyl-, isobutyl- and (iso)amyl octanoate) using lipase Palatase as the biocatalyst. The Taguchi design method was used for the first time to optimize the biosynthesis of esters by a lipase in an aqueous system of coconut cream and fusel oil. Temperature, time and enzyme amount were found to be statistically significant factors and the optimal conditions were determined to be as follows: temperature 30°C, fusel oil concentration 9% (v/w), reaction time 24h, pH 6.2 and enzyme amount 0.26 g. Under the optimised conditions, a yield of 14.25mg/g (based on cream weight) and signal-to-noise (S/N) ratio of 23.07 dB were obtained. The results indicate that the Taguchi design method was an efficient and systematic approach to the optimisation of lipase-catalysed biological processes.

Lipase-catalysed ester synthesis in solvent-free oil system: Is it esterification or transesterification?

Ester synthesis was carried out in a solvent-free system of lipase, coconut oil and ethanol or fusel alcohols to ascertain the reaction mechanism. During ester formation, octanoic and decanoic acids increased initially and then decreased gradually, indicating that ester production was a two-step reaction consisting of hydrolysis and esterification, rather than alcoholysis. With ethanol as the alcohol substrate, added butyric acid inhibited ester synthesis. However, when fusel alcohols were used as the alcohol substrate, no significant inhibitory effect by butyric acid was observed. Added octanoic acid did not show any adverse effect on the synthesis of corresponding esters. The results suggest that polarity of the reactants determines lipase activity. This study provides the first evidence on the mechanism of immobilised lipase-catalysed ester synthesis in a solvent-free system involving both hydrolysis and esterification.

Chemical and enzymatic synthesis of a library of 2-phenethyl esters and their sensory attributes

We report a simple enzymatic approach to synthesise phenethyl esters as natural flavouring materials. Chemical and lipase-catalysed esterification reactions between fatty acids of C4-C18 and 2-phenethyl alcohol were studied. Both methods were compared qualitatively and quantitatively by GC-MS/FID. The acid and thermal stabilities of 2-phenethyl esters were excellent and can meet the requirements of food matrices under most processing conditions. Sensory evaluation showed that each 2-phenethyl ester with a different carbon-chain-length fatty acid had unique sensory notes. Moreover, through Lipozyme TL IM-mediated transesterification, valuable 2-phenethyl alcohol-derived esters were synthesised from butter oil and 2-phenethyl alcohol. The influence of several physicochemical parameters (temperature, substrate molar ratio, enzyme loading, shaking speed and time) on the transesterification reaction was investigated to give optimal reaction conditions, leading to a high yield of 80.0%.

Synthesis and evaluation of odour-active methionyl esters of fatty acids via esterification and transesterification of butter oil

Methionol-derived fatty acid esters were synthesised by both chemical and lipase catalysed esterification between fatty acids and methionol. Beneficial effects of both methods were compared qualitatively and quantitatively by GC-MS/GC-FID results. And the high acid and heat stability of our designed methionyl esters meet the requirement of the food industry. Most importantly, the sensory test showed that fatty acid carbon-chain length had an important effect on the flavour attributes of methionyl esters. Moreover, through Lipozyme TL IM-mediated transesterification, valuable methionol-derived esters were synthesised from the readily available natural material butter oil as the fatty acid source. The conversion of methionol and yield of each methionyl ester were also elucidated by GC-MS-FID.