Institut für Pflanzenbiologie, Technische Universität Braunschweig, Mendelssohnstr. 4, D-38106 Braunschweig, Germany.
Plant Cell Physiol. 2010 Apr;51(4):546-53. doi: 10.1093/pcp/pcq019. Epub 2010 Mar 5.
In order to produce tradeable standard green coffee, processed beans must be dried. The drying procedure affects the abundance of relevant aroma substances, e.g. carbohydrates. Using molecular tools, the corresponding metabolic basis is analyzed. A decrease in water potential of the still living coffee seeds induces massive drought stress responses. As a marker for these stress reactions, accumulation of a general stress metabolite, GABA (gamma-aminobutyric acid), and associated gene expression of drought stress-associated dehydrins were monitored. The results of this study indicate that metabolism in drying coffee beans is quite complex since several events trigger accumulation of GABA. The first peak of GABA accumulation during drying is correlated with expression of isocitrate lyase and thus with ongoing germination processes in coffee seeds. Two subsequent peaks of GABA accumulation correspond to maxima of dehydrin gene expression and are thought to be induced directly by drought stress in the embryo and endosperm tissue, respectively. Apart from the significance for understanding basic seed physiology, metabolic changes in coffee seeds during processing provide valuable information for understanding the role and effect of the steps of green coffee processing on the quality of the resulting coffee.
为了生产可交易的标准绿咖啡，加工过的咖啡豆必须进行干燥。干燥过程会影响相关香气物质的丰度，例如碳水化合物。使用分子工具分析相应的代谢基础。仍存活的咖啡种子的水势降低会引起大量干旱胁迫反应。作为这些应激反应的标志物，积累一种普遍的应激代谢物 GABA（γ-氨基丁酸）和相关的干旱胁迫相关脱水素的基因表达被监测到。这项研究的结果表明，干燥咖啡豆中的代谢非常复杂，因为有几个事件会引发 GABA 的积累。在干燥过程中 GABA 积累的第一个高峰与异柠檬酸裂解酶的表达相关，因此与咖啡种子中的萌发过程有关。随后出现的 GABA 积累的两个高峰与脱水素基因表达的最大值相对应，分别被认为是胚和胚乳组织中干旱胁迫的直接诱导。除了对理解基本种子生理学的意义外，咖啡种子在加工过程中的代谢变化为理解绿咖啡加工步骤对所得咖啡质量的作用和影响提供了有价值的信息。
