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.