Paper accepted: Cymbopogon winterianus essential oil as an alternative source for producing terpenic esters with potential plant-protective antifungal activity using lipase immobilized on a lignin composite.

Today, Carlos Girão’s first paper containing results from his sandwich doctoral year with us in Münster has been accepted for publication in the journal Biocatalysis and Agricultural Biotechnology. Carlos has isolated lignin from cashew apple bagasse, a large side-stream of the cashew nuts industry in his native Brazil, and has immobilized a fungal lipase on it. Using this immobilized rather than the free enzyme, he was able to increase the yield when converting terpenic alcohols in the essential oil of lemongrass to terpenic esters. He came to us to determine the antimicrobial activities of these alcohols and esters towards phytopathogenic bacteria and fungi. Under the supervision of Dr. Carolin Richter, he found that esterifying geraniol and citronellol, the two main alcohols in the essential oil of lemongrass, to the respective butyric esters significantly increased their antifungal, but not their antibacterial activity. This improvement was seen both in an in vitro assay and in a plant infection assay. However, he did not observe it when he used the crude essential oil itself, probably because of a loss of antimicrobial citronellal (the aldehyde of citronellol) during the enzymatic esterification due to the high temperature of the process. Clearly, plant essential oils can be an important player when developing sustainable plant protectants. And from Carolin’s work together with Dr. Sruthi Sreekumar, we also know that they can act synergistically with plant protective chitosans, as exploited by our start-up in foundation “GreEnCAP technologies”.