1. Production and biological function of volatile esters in Saccharomyces cerevisiae
Sofie M G Saerens, Freddy R Delvaux, Kevin J Verstrepen, Johan M Thevelein Microb Biotechnol. 2010 Mar;3(2):165-77.doi: 10.1111/j.1751-7915.2009.00106.x.Epub 2009 Apr 6.
The need to understand and control ester synthesis is driven by the fact that esters play a key role in the sensorial quality of fermented alcoholic beverages like beer, wine and sake. As esters are synthesized in yeast via several complex metabolic pathways, there is a need to gain a clear understanding of ester metabolism and its regulation. The individual genes involved, their functions and regulatory mechanisms have to be identified. In alcoholic beverages, there are two important groups of esters: the acetate esters and the medium-chain fatty acid (MCFA) ethyl esters. For acetate ester synthesis, the genes involved have already been cloned and characterized. Also the biochemical pathways and the regulation of acetate ester synthesis are well defined. With respect to the molecular basis of MCFA ethyl ester synthesis, however, significant progress has only recently been made. Next to the characterization of the biochemical pathways and regulation of ester synthesis, a new and more important question arises: what is the advantage for yeast to produce these esters? Several hypotheses have been proposed in the past, but none was satisfactorily. This paper reviews the current hypotheses of ester synthesis in yeast in relation to the complex regulation of the alcohol acetyl transferases and the different factors that allow ester formation to be controlled during fermentation.
2. Single-crystal-to-single-crystal phase transition of 18β-glycyrrhetinic acid isopropyl ester
Dominik Langer, Barbara Wicher, Ewa Tykarska Acta Crystallogr B Struct Sci Cryst Eng Mater. 2022 Jun 1;78(Pt 3 Pt 2):450-458.doi: 10.1107/S2052520622002517.Epub 2022 Apr 30.
Due to the destruction of the integrity of the parent crystal, single-crystal-to-single-crystal phase transition in organic compounds is still a relatively rare phenomenon. The phase transition in glycyrrhetinic acid isopropyl ester is triggered by temperature change. The increasing volume of the isopropyl substituent as a result of increasing temperature forces a remodelling of the structural motifs. These changes cause a single-crystal-to-single-crystal phase transition. The low-temperature form is isostructural with glycyrrhetinic acid methanol solvate, while the high-temperature phase is isostructural with the ethyl ester of this acid.
