CBMA-Centre of Molecular and Environmental Biology, University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal.
Molecules. 2020 Dec 28;26(1):91. doi: 10.3390/molecules26010091.
Monoterpenes are plant secondary metabolites, widely used in industrial processes as precursors of important aroma compounds, such as vanillin and (-)-menthol. However, the physicochemical properties of monoterpenes make difficult their conventional conversion into value-added aromas. Biocatalysis, either by using whole cells or enzymes, may overcome such drawbacks in terms of purity of the final product, ecological and economic constraints of the current catalysis processes or extraction from plant material. In particular, the ability of oxidative enzymes (e.g., oxygenases) to modify the monoterpene backbone, with high regio- and stereo-selectivity, is attractive for the production of "natural" aromas for the flavor and fragrances industries. We review the research efforts carried out in the molecular analysis of bacterial monoterpene catabolic pathways and biochemical characterization of the respective key oxidative enzymes, with particular focus on the most relevant precursors, β-pinene, limonene and β-myrcene. The presented overview of the current state of art demonstrates that the specialized enzymatic repertoires of monoterpene-catabolizing bacteria are expanding the toolbox towards the tailored and sustainable biotechnological production of values-added aroma compounds (e.g., isonovalal, α-terpineol, and carvone isomers) whose implementation must be supported by the current advances in systems biology and metabolic engineering approaches.
单萜是植物次生代谢物，广泛应用于工业生产过程中，作为重要香气化合物的前体，如香草醛和(-)-薄荷醇。然而，单萜的物理化学性质使得它们难以通过常规方法转化为高附加值的香气。生物催化，无论是使用完整细胞还是酶，都可以克服当前催化过程中产物纯度、生态和经济限制，以及从植物材料中提取等方面的缺陷。特别是氧化酶（如加氧酶）具有修饰单萜骨架的能力，具有高区域和立体选择性，这对于为风味和香料行业生产“天然”香气很有吸引力。我们综述了细菌单萜代谢途径的分子分析和各自关键氧化酶的生化特性方面的研究进展，特别关注了最相关的前体，β-蒎烯、柠檬烯和β-月桂烯。目前的研究进展表明，单萜分解细菌的专门酶组合正在扩展工具包，以实现定制化和可持续的生物技术生产高附加值香气化合物（如异缬草酸、α-松油醇和香芹酮异构体），这需要系统生物学和代谢工程方法的当前进展来支持。
