Structure-guided engineering of medium- and long-chain triglycerides:​Fermentation-assisted biosynthesis, structural control and future perspective

Medium- and long-chain triglycerides (MLCTs) are triacylglycerols (TAGs) that have medium-chain fatty acids (MCFAs) and long-chain fatty acids (LCFAs) linked together on a single glycerol backbone. The positioning of the components, such as the MCFA-LCFA-MCFA (MLM-type) positioning, can affect lipase-mediated hydrolysis, release of fatty acids (FAs), absorption and metabolic behavior, however, structure-function relationships requires experimental validation. This review presents a comparison between chemical interesterification, lipase-catalyzed interesterification and fermentation-assisted biosynthesis of MLCT. Chemical interesterification will redistribute fatty acyl groups, but offers​ limited positional control, while lipase-catalyzed synthesis provides more positional selectivity but is susceptible to acyl migration. Fermentation-​assisted biosynthesis is a prospective approach that connects FA chain-length control, acyl-CoA supply and TAG assembly more strongly. However, there is currently more evidence that strongly supports the production of tailored FAs by microbes than demonstrated positional control of MLCT molecular species. Structural validation requires intact TAG molecular species analysis, positional analysis, and stereospecific analysis. An integrated framework combining applications of structural analysis, selective biocatalysis, fermentation optimization, metabolic engineering and functional evaluation is proposed.