Sustainable biodiesel production from Ficus nitida leaves through the in-situ bioconversion of membrane galactolipids by Talaromyces thermophilus galactolipase

Galactolipids constituting the chloroplast membranes in photosynthetic organisms represent the main reservoir of fatty acids on earth. This abundant resource is, however, completely untapped. Galactolipids are not accessible by simple physical means as vegetable triacylglycerols since they are dispersed in plant biomass. Here, we establish that Talaromyces thermophilus lipase (TTL), with a high galactolipase activity, has the capacity to hydrolyze and fully convert the natural galactolipids of dried Ficus nitida leaves as a non-oilseed green feedstock to produce fatty acids (FA) and fatty methyl esters (FAME), respectively. Its high galactolipase activity was further explored by performing in-situ transesterification reaction on the whole green biomass. Thus, a successful system for one-pot procedure was developed. Optimized methanolysis conditions were obtained with a lipid/methanol molar ratio of 1/6, chloroform as a co-solvent, a temperature of 37 °C and 660 U of free TTL for 750 mg of dried F. nitida leaves pretreated with glycosyl hydrolases. After 12 h of reaction, 121 ± 8.2 mg of biodiesel was obtained, of which 66 % was composed of FAME(s) and 33 % was composed of alkanes (C16-C24). 80 ± 1.14 mg of FAME(s) were converted from galactolipid FA within leaves with a recovery yield of 89 %. The methanolic extract of F. nitida leaves was evaluated as an antioxidant source and could help prevent the oxidation process of the polyunsaturated FAME(s) produced. Lastly, recovering and/or converting galactolipid FA in green biomass shows promise as a way of producing molecules with a potential to co-refine in existing petroleum refineries and to avoid competing interests with vegetable oils.