Using Enzymes to Harvest Fatty Acids from Galactosyldiacylglycerols, the Most Abundant Lipids in Plant Biomass

Mono- and digalactosyldiacylglycerols (MGDG, DGDG), the main lipids of plant photosynthetic membranes, represent a large but unexploited reservoir of fatty acids on earth. They are dispersed in plant biomass (milligrams per gram of dry mass) and not as accessible as vegetable oils by simple physical means. The identification and characterization of galactolipid acyl hydrolases, or galactolipases, raise the possibility to use these biocatalysts for the bioconversion of galactolipids. Here, we show that two enzymes of mammalian and microbial origins, pancreatic lipase-related protein 2 from guinea pig (GPLRP2) and cutinase from Fusarium solani, have the capacity to directly and fully release the fatty acids of MGDG and DGDG present in various plant leaves and green wastes. This high substrate accessibility to enzymes was further explored by performing alcoholysis reactions in situ and showing the conversion of galactolipid fatty acids into fatty acid alkyl esters (FAAE) when the enzyme and leaves were incubated in the presence of 6 or 2.5 M ethanol. These findings pave the way to the recovery of fatty acids dispersed in green biomass and the exploitation of an additional and renewable source of fatty acids for oleochemistry and nutrition in a context of competition for vegetable oils.