Highly active and stable Fe3O4/Au nanoparticles supporting lipase catalyst for biodiesel production from waste tomato

Snowman-like Fe3O4/Au nanoparticles (NPs), made up of small Au nanoparticles grown on larger magnetite NPs, were used to directly bond lipase (E.C.3.1.1.3) from Thermomyces lanuginosus (TL), through physical interactions including interfacial activation. Immobilized lipase was able to hydrolyse olive oil triglycerides with high activity (up to 109%, activity of the immobilized enzyme compared to that of its free form, at pH = 7, standard deviation (SD) of 2.1). Improved stability, derived from gold based NPs, was observed with temperature and pH (e.g. 334.9% at pH = 8.5,...). Specifically, snowman-like NPs were used to catalyse the transesterification of tomato seed oil and their activity was compared with that obtained with the free enzyme and the enzyme immobilized on Fe3O4 NPs alone. At a lipase concentration of 20%, reaction temperature of 45 degrees C, oil/methanol ratio 1: 6 obtained by adding two times methanol to a 1:1 M initial solution, with a reaction time of 24 h, immobilized lipase exhibits a remarkable biodiesel yield of 98.5%. In particular, it shows the following: fatty acid methyl ester (FAME) composition in accordance to that of the extracted tomato seed oil; ester (97.2% +/- 0.26) and linolenic methyl ester (4.3% +/- 0.22 contents) in compliance with EN14103 methods and in agreement with EN14124 requirements. The highest activity was observed at a molar ratio oil/methanol of 1: 6 M. It is worth noting, that in transesterification reactions, in contrast with the behaviour shown for hydrolysis, lipase anchored on snowman-like NPs results more active than on magnetite alone. The immobilized lipase activity stays above 84% after three cycles of use, showing an excellent reusability also due to the stabilizing effect of gold. (C) 2018 Published by Elsevier B. V.