Theoretical screening methods are based on a thermodynamic
description of the investigated system. Here, the
selection of solvents is based upon the solubility parameters
of solvent–solute systems. The useful prediction
method proposed by Yamamoto was applied to calculate
HSPs of alternatives solvents and terpenes in blackcurrant
extracts (Table 1). Two dimensional (2D) graph of dp versus
dh parameters (Fig. 3) shows the different aromas in
blackcurrant and the different alternative solvents according
to Hansen’s parameters. The influence of the structure
of the molecule on polarity is presented. In fact, terpenes
and n-hexane display similar HSP values, whereas
oxygenated compounds have different HSPs due to their
hydroxyl group or carboxyl group, which resulted in a
higher dh value. The calculated HSP values were close to
those of some alternative solvents, which demonstratedthat terpenes may dissolve in these alternative solvents
according to the principle ‘‘like extracts like’’. The relative
energy difference (RED) numbers have been used to
characterize and quantify solute–solvent interactions.
Table 3 represents the RED modelling optimization of
solvents for the extraction of target terpene. All solvents
(0 < RED < 1) that were close to the centre (RED = 0) could
be considered as good solvents for each terpene. The
solubility of alternative solvents used in the extraction of
target solutes has been respectively characterized using
the 2D graph for an easy understanding of the solubility of
various solvents in solid–liquid extraction. (circles materialize
the prediction data). The alternative solvents showed
various theoretical solubilities for each terpene, with a
significant difference that would be validated by experiments.
This result could be explained by the difference in
the solvents’ polarities. Hexane and a-pinene included
clusters of monoterpenes and sesquiterpenes. Indeed,
a-pinene solvent showed solubility parameters with
aroma compounds similar to those of hexane. MeTHF
and ethyl acetate are more polar than hexane, and thus
included clusters of oxygenated monoterpenes (aldehydes
and ketones).