3.2. Oleoresin Composition
In parallel with the extraction efficiency results, it was not
surprising to observe that the solvent type had significant (P< 0.05) effect on the total lipid, protein and phenolic
content of oleoresins.
Following
the traditional solvent extraction approach, the highest protein (0.67 ±
0.03 wt%), lipid (69.22 ± 0.04 wt%) and phenolic contents (48 ± 0.01
mg GAE/g) were obtained with IL1 (Table 1). The lowest
extraction for protein (0.36 ± 0.02 wt%) was obtained using
dichloromethane, while the lowest lipid (53.12 ± 0.08 wt%) and phenolic
contents (21 ± 0.02 mg GAE/g) were observed using ethanol. Wet milling
extraction with a ball mill increased (P < 0.05) the
total lipid (82.19±0.07 wt%), protein (1.37 ± 0.05 wt%), and phenolic
content (57 ± 0.01 mg GAE/g) of oleoresin when IL1 used
as compared to total lipid ( 69.22 ±0.04 wt%), protein 0.67 ± 0.03
wt%), and phenolic content (48 ± 0.01 mg GAE/g) with traditional
extraction (Table 1). In a similar way to traditional extraction,
IL1 and IL2 were same (P> 0.05) for lipid, protein, phenolic content. Jin et. al
(2022) also found that using ball mill increased the overall content of
protein, fat, and volatile compounds in the sesame seed extracts as
compared to colloid and stone mills. The increase was higher for protein
(51.1%) than lipid (15.8 %) at the conditions for the highest
extraction yield when IL is used (Table 1).
The fatty acid composition of the oleoresins was analyzed by using gas
chromatography and shown in Table
2. Oleic acid, palmitic acid, palmitoleic acid and myristic acid were
the most abundant fatty acids in all the oleoresins. Octadecanoic acid
was present only in trace amounts for all extracts with a concentration
range between 0.292 to 1.792%. This aligned with the fatty acid content
of raw sorghum varieties of reported in previous studies
(Espitia-Hernández et al., 2022). The solvent type had a significant
(P < 0.05) effect on the fatty acid
composition. The unsaturated
fatty acids (oleic and palmitoleic acids) increased more than saturated
ones (myristic and palmitic acids) when ILs were used instead of
dichloromethane and ethanol. This was probably related to the double
bonds of unsaturated fatty acids that provided lower free energy for
temporal ionization and to interact with cations and anions of ionic
liquids. In another study, Li et al. (2009) showed that higher
polyunsaturated fatty acid extracts from cod liver oil were obtained
with ILs in comparison to organic solvents, such as acetone, methanol,
acetonitrile, and chloroform. The percentages of oleic, palmitic and
myristic acids were not significantly (P > 0.05 )
different when IL1 and IL2 were used
with traditional extraction process while it was significantly (P
< 0.05 ) different for palmitoleic acid. In contrast, the
percentage of these fatty acids were significantly (P <
0.05 ) different when dichloromethane or ethanol was used. The
concentrations of both oleic and palmitic acids were significantly
(P < 0.05 ) lower with both traditional solvents than
ILs when traditional extraction was conducted.
The extraction method also had a significant (P < 0.05 )
effect on the fatty acid composition (Table 2). The percentage of oleic
and palmitoleic acids significantly (P < 0.05 )
increased while myristic and palmitic acids significantly (P
> 0.05 ) decreased when ball milling process was conducted
instead of traditional process. The highest concentration of oleic acid,
the most abundant unsaturated fatty acid in the oleoresins was 23.663%
± 0.003 with the combined action of ball milling and
IL1. In addition to this, the increase in oleic acid was
45.89% and 29.15% when ball milling was used with IL2and ethanol respectively, as compared to traditional solvent extraction
with the same solvents. On the other hand, the decrease in myristic acid
was 24.57% and 34.44% when ball milling was used with
IL2 and ethanol respectively, as compared to traditional
extraction using IL2 and ethanol. Similar changes in
unsaturated (palmitoleic and oleic acids) and saturated (myristic and
palmitic acids) fatty acid concentrations were observed by Korber et. al
(2022) where ball mill extraction was applied for lettuce plants
(Lactuca sativa L.) to extract galactolipids and sulfolipids.
Furthermore, the percentages of oleic, palmitoleic, myristic and
palmitic acids were not significantly (P > 0.05 )
different when IL1 and IL2 were used
with ball milling extraction. Similar to the traditional extraction, the
percentage of these fatty acids changed when dichloromethane and ethanol
were selected. The use of ILs increased (P < 0.05 ) the
total phenolic content of the oleoresins.
Oleoresins were rich in eight
phenolic compounds: caffeic acids, coumaric acid, ferulic acids,
apigenidin, luteolidin, 7-methoxy apigeninidin, eriodictyol and
narencenin (Table 3). The HPLC chromatogram was given in Supplementary
Materials (Fig. S1). Caffeic acid, coumaric acid and luteolidin were the
major phenolic compounds present in all oleosome samples. Among these,
caffeic acid followed by coumaric acid were the most abundant and they
remained so with all types of solvents. The solvent type significantly
(P < 0.05) affected the total phenolic content and
composition (Table 3). The percent increase in caffeic acid was 74.84%
when IL1 was used instead of dichloromethane with the
traditional extraction process. In addition to this, there was no
significant (P > 0.05) difference between
IL1 and IL2 while ethanol and
dichloromethane showed significant (P < 0.05)
difference using the same extraction method.
The extraction method also had a significant (P < 0.05 )
effect on the phenolic composition (Table 3). The increase in caffeic
acid was 28.93% and 50.16% when ball milling was combined with
IL1 and dichloromethane respectively, as compared with
the traditional extraction process using the same solvents. Similar
effects were observed in luteolinidin when ball milling and traditional
extraction processes were compared: the increase in luteolinidin was
21.78% and 57.68% when ball milling extraction was performed with
IL2 and ethanol respectively, as compared with
traditional extraction. Furthermore, the percentages of caffeic acid
were not significantly (P > 0.05 ) different when
IL1 and IL2 with the combined action of
ball milling process, but there was a slight significant difference when
ethanol and dichloromethane were used. Similarly, in another study,
Talekar et al. (2019) showed that total phenolics and antioxidant
“punicalagin” increased when ball-mill pre-treatment was used for
pomegranate peel waste, and it was more efficient than
ultrasound-assisted and Soxhlet extraction.