Irrigated and CO2 level effects on metabolism in Coffea arabica beans from mixture design - near infrared fingerprints

Coffee bean metabolites are regulated in response to environmental factors, such as climate change and abiotic stress that could influence the quality of beverage. Therefore, the development of methodologies that can indicate chemical changes owing to these perturbations becomes important for making decisions about the coffee culture future. The present study proposes an exploratory analysis of metabolic changes of Coffees arabica beans by means of the spectral fingerprints acquired by Near Infrared Spectroscopy (NIR) combined with Principal Component Analysis (PCA). Coffee plants were cultivated in Free-Air Carbon dioxide Enrichment (FACE) experiment under two CO2 levels, current or elevated, supplied with irrigation or cultivated under rainfed conditions (unirrigated). When measurements were made directly on the raw coffee beans in reflectance mode, the results of the NIR spectra fingerprints did not discriminate the coffee beans originated from different cultivation conditions. An alternative methodology was proposed, using NIR spectral fingerprints in transmittance mode obtained from the statistical mixture design extract solutions. Among ethanol, dichloromethane, hexane, ethyl ether and their combinations, the PCA showed that pure ethanol and the mixture involving ethanol and dichloromethane (1:1 v/v) were the solvents permitting the coffee beans discrimination. A larger number of samples then confirmed the discrimination between the different CO2 levels and irrigation conditions for these extracts. Bands in different regions were responsible for these discriminations and were different for extracts of ethanol and the mixture ethanol and dichloromethane. Results indicate that labeling depends on the intrinsic properties of the organic matrix and the type of solvent used. Furthermore, in the impossibility of an exploratory analysis of the NIR spectra acquired directly on the raw coffee beans, the experimental design, to obtain extracts using different solvents, associated with the obtaining of the spectral fingerprints in the NIR region in transmittance mode, showed an alternative to this situation.