2.2. Preparation of Oleoresin
Oleoresin were extracted from ground waxy burgundy whole sorghum grain
with or without wet milling using traditional (ethanol, dichloromethane)
and novel solvents (IL1 and IL2). The
traditional extraction without ball milling was done following the
method of Khasanah et. al (2017) with some modifications. A batch of
whole grain sorghum (50 g) was soaked in NaHCO3 (0.1 M)
at 1:1 (w/v) ratio 12 h at 21 ± 2 oC. The soaked
sorghum grains were ground using a high-shear blender (Waring
Commercial, Model 7011BU, McConnellsburg, PA, USA) at the highest speed
(22000 rpm) with three-time intervals of 5 minutes. The ground sorghum
(10 g) and the solvent (40 mL) were mixed using a magnetic stirrer for
30 minutes. The slurry was filtered through a cheese cloth to remove the
undissolved solids. The filtrate was centrifuged at 3000 x g for
15 min at 20 ± 2 oC to separate oleoresin-rich organic
top layer, which was collected in hermetically sealed glass tubes. The
extraction from the filtrate repeated three times until no sediment was
visible. The weight of sediment and organic phase was recorded in each
dilution step for calculation of the extraction yield. The oleoresins
were concentrated by removing the solvent using a refrigerated vapor
trap (Savant™ SpeedVac™, RVT5105, Model SPD300DDA, Thermo Fisher
Scientific, Marietta, OH, USA). The wet milling extraction was done
using the same sorghum and solvent mixture by using a ball mill (Retsch,
PM 100 type, Retsch GmbH, Germany) equipped with a milling bowl (250 mL)
and ceramic balls (diameter:10 mm; quantity: 100 pieces) and operated at
500 rpm with 2 cycles of 15 minutes. The filtrate containing the
oleoresin was separated and concentrated similar to traditional
extraction.