Nestlé Research Center, P.O. Box 44, 1000 Lausanne 26, Switzerland.
J Agric Food Chem. 2011 Oct 26;59(20):11196-203. doi: 10.1021/jf201758h. Epub 2011 Sep 29.
The relationship between the physical structure of espresso coffee foam, called crema, and the above-the-cup aroma release was studied. Espresso coffee samples were produced using the Nespresso extraction system. The samples were extracted with water with different levels of mineral content, which resulted in liquid phases with similar volatile profiles but foams with different structure properties. The structure parameters foam volume, foam drainage, and lamella film thickness at the foam surface were quantified using computer-assisted microscopic image analysis and a digital caliper. The above-the-cup volatile concentration was measured online by using PTR-MS and headspace sampling. A correlation study was done between crema structure parameters and above-the-cup volatile concentration. In the first 2.5 min after the start of the coffee extraction, the presence of foam induced an increase of concentration of selected volatile markers, independently if the crema was of high or low stability. At times longer than 2.5 min, the aroma marker concentration depends on both the stability of the crema and the volatility of the specific aroma compounds. Mechanisms of above-the-cup volatile release involved gas bubble stability, evaporation, and diffusion. It was concluded that after the initial aroma burst (during the first 2-3 min after the beginning of extraction), for the present sample space a crema of high stability provides a stronger aroma barrier over several minutes.
研究了浓缩咖啡泡沫（称为咖啡脂）的物理结构与杯顶香气释放之间的关系。使用 Nespresso 提取系统生产浓缩咖啡样品。这些样品是用不同矿物质含量的水提取的，结果得到了挥发性相似但泡沫结构特性不同的液相。使用计算机辅助显微镜图像分析和数字卡尺定量测量泡沫体积、泡沫排水和泡沫表面的薄片膜厚度等结构参数。通过 PTR-MS 和顶空采样在线测量杯顶挥发性浓度。对咖啡脂结构参数与杯顶挥发性浓度之间的相关性进行了研究。在咖啡提取开始后的头 2.5 分钟内，泡沫的存在会增加选定挥发性标志物的浓度，而不管咖啡脂的稳定性如何。在 2.5 分钟以上的时间里，香气标志物的浓度取决于咖啡脂的稳定性和特定香气化合物的挥发性。杯顶挥发性释放的机制涉及气泡稳定性、蒸发和扩散。结论是，在初始香气爆发（提取开始后的头 2-3 分钟内）之后，对于当前的样本空间，高稳定性的咖啡脂在几分钟内提供了更强的香气屏障。
