3.1. Effect of extraction conditions on yield
The solvent type had a significant (P < 0.05) effect on
the extraction yield of oleoresins (Fig. 1). Overall, ILs increased
(P < 0.05 ) the extraction yield (25.11 ± 0.84 wt% for
IL1 as compared to 18.37 ± 1.34 wt% for ethanol) via
traditional extraction (i.e., without ball milling) (Fig.1). The higher
extraction efficiencies with the imidazolium based ILs were as expected
due to the combined extractive power of the composite systems. In a
similar way, other researchers showed that imidazolium based ILs can
increase the extraction yield of bioactive phytochemicals, such as
flavonoids, alkaloids, caffein, etc., from plant tissue (Bogdanov &
Svinyarov, 2013; Claudio et. al, 2013). The increase in the extraction
efficiencies can be explained by the combination of dipole, ionic, and
hydrophobic interactions
of the IL components. In parallel
to the extraction efficiency, lipid, protein, and phenolic compositions
were also significantly (P < 0.05) affected by the extraction
conditions as discussed in the following sections (Table 1). The
efficiency of traditional solvent extraction with ethanol and
dichloromethane was the same (P > 0.05); however, the
compositions of their oleoresin extracts were different. There was no
significant difference (P > 0.05 ) in the extraction
yield of two ILs as well (Fig. 1). Thus, the difference between the type
of charged groups in ILs was not responsible for breaking the solid
enclosure required for extraction. In a recent study, Cheng et. al
(2020) used different ILs with 11 anions and 8 imidazolium-based cations
including the ILs in our study for extraction of isoflavone compounds
from Puerariae lobatae. They showed that the extraction
efficiencies of the ethyl and hexyl substituted imidazolium ILs were the
same, yet changed with ion concentration in their solution. Therefore,
we can conclude that imidazolium ILs regardless of the cation and anion
composition were more effective than traditional solvents due to their
ability to disrupt cellular structure that determine extraction
capacity. On the other hand, the chemical difference between the two ILs
affected the oleoresin composition (Table 1) as discussed later.
The wet milling process with a ball mill significantly
(P < 0.05)
increased the extraction yield as compared to traditional solvent
extraction. For example, the
extraction yield increased more
than 50% when IL2 was used with ball mill (31.36 ± 1.01
wt%) as compared to traditional batch extraction (18.92 ± 0.68 wt%)
(Fig. 1). This can be explained by the ability of ball mill to break
down the integrity of the hard enclosure trapping the oleoresins via
omnidirectional impact of the beads and associated high shear.