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The increased awareness and research for improvements and valorization of by-products from established processes is marking the recent years as an important moment for biorefinery processes. Under the biorefinery scope, several biomasses are regaining interest for valorization, as the knowledge of sources and product certification rises. Essential oils are a classical example of a different approach for forestry residues valorization, coexisting with a different class of extracts obtained from biomass extraction, plant extracts [1].

In the present work, distinct methods were employed for E. globulus leaves extraction. Conventional techniques, namely Soxhlet, and solid-liquid extraction in batch mode (SLE-batch) at four different temperatures (20, 35, 55 and 75 °C), were performed with solvents of distinct polarity: dichloromethane, ethanol, methanol, n-hexane, petroleum ether, ethyl acetate and isopropanol. To obtain the essential oil of the E. globulus leaf, hydrodistillations were performed. Supercritical CO₂ extractions were also performed at 300 bar and 40 °C, with the addition of modifiers to CO₂, namely ethanol and ethyl acetate, in contents of 5-10 wt.%.

All the extracts produced, along with the ground E. globulus leaf, commercial samples of E. globulus leaf oil obtained by steam-distillation from Portugal and India, pure eucalyptol and betulinic, oleanolic and ursolic acids, were analyzed with Fourier transform infrared – attenuated total reflectance (FTIR-ATR) technique.

To avail from all the information of the FTIR-ATR spectra, a statistical tool, multidimensional scaling (MDS), was employed. MDS enables the representation of similarities/dissimilarities between complex data as distances in a low-dimensional space, allowing its visual interpretation and analysis [2].

The extractions performance varied significantly with the method and solvent employed, along with the temperature in the SLE-batch runs. The yields of extraction obtained ranged from 0.14 wt.% to 37.80 wt.% for hydrodistillation and Soxhlet extraction with methanol, respectively. All SLE-batch experiments scored lower than the Soxhlet ones. Furthermore, within the SLE-batch experiments, temperature had a clear effect, as lower temperatures yielded less and vice-versa. The supercritical extractions yields were similar to the less polar solvents, but higher than those of hydrodistillation.

MDS provided a scale reduction from 1000 D to 2 D with a stress factor of 9.9 %, considered good [2]. From its visualization, a clear distinction of the extraction methods employed can be observed, along with solvent polarity and temperature effect.

In this work, an experimental and modeling study on E. globulus leaf was performed, aiming at mapping the similarities/dissimilarities between natural products that can be produced by extraction from this biomass.On the whole, this study is expected to shed light on the biorefinery opportunities for this biomass part, including a valid enrichment of product portfolio options or market segments.

References

1. 1. G. Vânia G. Zuin, L.Z. Ramin, Green and Sustainable Separation of Natural Products from Agro-Industrial Waste: Challenges, Potentialities, and Perspectives on Emerging Approaches (Springer, 2018)
2. 2. Borg, P.J.F. Groenen, P. Mair, Applied Multidimensional Scaling (Springer, Berlin, 2013)