Search

The main objectives of this work were to investigate the purification of soybean lipoxygenase (LOX) by using membrane filtration, the characterisation of soybean lipoxygenase and hydroperoxide lyase and the application of soybean lipoxygenase for the bioconversion of a flavour compound (n-hexanal) via lipoxygenase pathway. The feasibility of removing the bulk of soybean soluble proteins and lipoxygenase from soybean crude extract using crossflow microfiltration was first demonstrated. The optimal operation parameters for the membrane filtration were evaluated. A dialfiltration process was developed to remove soluble proteins from soybean crude extract solution. Afterwards, the permeate protein solution was subjected to the concentration by ultrafiltration. The recovery and purification of soybean lipoxygenase after membrane process were 53% and 2.15, respectively. The optical pH of LOX from soybean crude extract (FI), membrane-purified solution (FII) and further purification by precipitation with saturated (NH4)2SO4 (FIVb) indicated only soybean LOX-1 existed in this enzyme source, which was also confirmed by the analysis with ion exchange chromatography. The results also showed that FIVb, precipitated by ammonium sulphate at 40-60% of saturation, had the highest specific activity and recovery. Hydroperoxide lyases (HPL) from enzymatic sources have optimal pH of 7.0. However, only 28.5% of total HPL activity remained in Fraction FII with respect to that of Fraction FI, indicating deletion of this enzyme during the membrane filtration. Using LOX preparations, the production of n-hexanal compounds was carried out using linoleic acid as a substrate. Different reaction conditions for the n-hexanal bioconversion, such as pH, protein and substrate concentrations, addition of surfactant and oxygen, were determined in two different soybean enzymatic sources. Fraction FI had higher efficiency for n-hexanal bioconversion than that of Fraction FII. The results showed the enzyme reactor that has the feasibility of n-hexanal compound produced by soybean crude extract and linoleate in a large-scale bioreactor.