Life Sciences und Facility Management, Zurich Univeristy of Applied Science, Einsiedlerstrasse 31, 8820 Wädenswil, Switzerland.
J Agric Food Chem. 2011 Sep 14;59(17):9074-9. doi: 10.1021/jf201918a. Epub 2011 Aug 19.
Among the 100 different known Coffea species, Coffea arabica L. (Arabica) and Coffea canephora Pierre (Robusta) are the only two of commercial interest. They differ in a range of agronomic, genetic, and chemical properties. Due to the significant price difference between Arabica and Robusta, there is an economic incentive to illicitly replace Arabica with Robusta. Therefore, it is crucial to have accurate methods to determine the Robusta-to-Arabica-ratio in blends. This paper presents the proof of principle of a new and fast approach to determine the Robusta fraction in a blend based on Raman spectroscopy. The oils of two references (a pure Robusta and pure Arabica coffee) and six blends thereof consisting of different Robusta and Arabica fractions were extracted using a Soxhlet system. The solutes were analyzed by means of Raman spectroscopy without further workup. Using the intensity ratio between two Raman peaks, one characteristic for kahweol and one characteristic for fatty acids, allowed determinination of the Robusta content in a given mixture. The intensity ratio is linearly dependent on the Robusta content of the compound. Above a Robusta content of 75 wt %, kahweol was not detectable. The Raman data are in agreement with results obtained from the very time-consuming multistep DIN 10777 procedures based on HPLC.
在 100 种已知的咖啡物种中，咖啡阿拉比卡（Arabica）和咖啡罗布斯塔（Robusta）是唯二具有商业价值的两种。它们在农艺学、遗传学和化学性质方面存在一系列差异。由于阿拉比卡和罗布斯塔之间存在显著的价格差异，因此存在将阿拉比卡非法替换为罗布斯塔的经济动机。因此，拥有准确的方法来确定混合物中的罗布斯塔与阿拉比卡的比例至关重要。本文提出了一种基于拉曼光谱快速确定混合物中罗布斯塔比例的新方法的原理证明。使用索氏提取系统从两种参考油（纯罗布斯塔和纯阿拉比卡咖啡）和由不同罗布斯塔和阿拉比卡比例组成的六种混合物中提取油。通过拉曼光谱分析溶质，无需进一步处理。使用两个拉曼峰之间的强度比，一个特征峰是卡瓦醇，另一个特征峰是脂肪酸，可以确定给定混合物中的罗布斯塔含量。该强度比与化合物中罗布斯塔含量呈线性相关。罗布斯塔含量高于 75wt%时，无法检测到卡瓦醇。拉曼数据与基于 HPLC 的非常耗时的多步 DIN 10777 程序的结果一致。
