Evaluation of the stability of immobilized lipases from Rhizomucor miehei and Rhizopus oryzae in high oleic sunflower oil
Abstract: Lipase is one of the most useful enzymes in food industry, which can catalyze the hydrolysis and the synthesis of esters. However, the high cost due to the poor operation stability of lipase hinders the wide use of it. In present research, the stability of lipases in aqueous systems has been thoroughly studied, while research on lipases in non-aqueous systems is limited. In this work, the secondary oxidation products of high oleic sunflower oil (HOSO) were determined by HPLC and LC-MS. Formaldehyde, acetaldehyde and hexaldehyde which were confirmed in oxidized oil were selected to test their deactivation effect to two commercial pre-immobilized lipases (Novozym 40086 and lipase DF Amano 15) in non-aqueous system. In addition, the influence of oleic acid and commercial antioxidants (citric acid, tocopherol dl-alpha, tocoblend L70 IP, Tert-Butylhydroquinone (TBHQ) and Rosal-OX LR W/D) on the lipase stability was tested. In order to improve the stability of lipase in the presence of these harmful chemicals, lipase from Rhizomucor miehei was immobilized on MP1000, and the stability of it was tested in the presence of oxidized oil and three detected aldehydes to evaluate the effect of MP1000. The oxidized HOSO and oleic acid were found to cause deactivation of lipases. Citric acid in all concentrations and high concentration of tocoblend L70 IP and tocopherol dl-alpha were found to cause significant deactivation of Novozym 40086 and lipase DF Amano 15. Suitable amount of tocopherol dl-alpha (0.2%), tocoblend L70 IP (0.2%), TBHQ (0.2-1.0 mg/g) and Rosal-OX LR W/D (1.6-3.2 mg/g) would not cause inactivation for Novozym 40086 and lipase DF Amano 15. Lipase RM on MP1000 has better resistance to oxidized oil than that on acrylic resin bead (Novozym 40086).
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