Sequential mixture design optimization for divergent metabolite analysis: Enriched carbon dioxide effects on Coffea...

The first metabolic study of the impact of elevated CO₂ (590 µL CO₂ L^-1) levels on the leaves and buds of Coffea arabica L. plants is reported. A novel sequential statistical mixture design strategy allowed optimization of both the extraction and mobile phase solvent systems to increase differences detected in metabolites of Coffea arabica L. plants and buds. Factor analysis showed that the 227 and 273 nm bands of the 1:1:1 ternary ethyl ether - dichloromethane - methanol mixture spectra resulted in discrimination of elevated CO₂ extract samples from those obtained from leaves grown in a current level CO₂ atmosphere (390 µL CO₂ L^-1) of leaf sample extracts. DAD-HPLC spectral peak evidence showed a 32% increase in absorbance of the 273 band for the enriched CO₂ leaf extracts. This band has been assigned to caffeine-like substances and confirmed by the mass spectral signal at m/z 195 ([M + H]⁺). No enrichment band increases were found for kahweol, kaempferol and quercetin that had presence confirmed by mass spectral analysis. No epigenetic effect of this metabolic profile was found in new leaves after the addition of CO₂ stopped. Enriched CO₂ perturbation of the bud metabolite were much smaller than for the leaf samples. Absorbance increases in the 228 nm and decreases in the 235 nm bands play a prominent role in the discrimination of enriched CO₂ buds from the controls in the pure dichloromethane extracting solvent. This global metabolome strategy allows the monitoring of chemical groups of plants susceptible to environmental changes as well as elucidate metabolic variations in complex matrices of biochemical responses.