Introduction
Oleoresins are phytocomplexes extracted from plant sources, herbs and oilseeds as oil-rich viscous materials. These resinous extracts include terpenoids, fatty acids, phospholipids, essential oils, proteins, and phenolic compounds (Napoli et al., 2019). Oleoresins offer great potential for value-added food applications (e.g., beverages, sauces and meat products, baked products, and confectionaries) related to their chemical stability, uniformity, complex composition of biopolymers, lipids, polar lipids, and health beneficial phytochemicals. Oleoresins carry surface active molecules, such as phospholipids and proteins. The interactions between these proteins, triacylglycerols and phospholipids are responsible for the integrity and stability of their dispersions and emulsions.
The extraction method plays an important role in the stability, composition, yield and structural characteristics of oleoresins. Conventional solvent extraction involves the use of organic solvents, such as ethanol, hexane or ethyl acetate, to simultaneously obtain volatile and non-volatile phytochemicals with functional properties (Khasanah et al., 2017). Ultrasound- and microwave-assisted extraction systems were used to increase the extraction yield (Ayub et al., 2023). Wet milling strategies, such as ball milling, can be used to improve the extraction efficiency by breaking solid enclosures where the oleoresins are trapped. For example, ball milling was used to extract sesame paste from seeds with improved viscosity and reduced particle size (Jin et al., 2022). A similar strategy was used for the improving the functional properties of the proteins, such as surface activity, solubility, and hydrophobicity of proteins extracted from hempseed (Julakanti et al., 2023).
In addition to the extraction method, the type of solvent determines the extraction efficiency and physicochemical properties of the oleoresins. The poly-ionic liquids (ILs) are molten organic salts below 100oC, which combine the characteristics of different ionic chemicals, received considerable attention as substitutes of volatile organic solvents due to their versatility, less toxicity, remarkable solubilization for organic and inorganic compounds (Tolesa et al., 2017). ILs offer great potential to enhance the extraction efficiencies for complex material, such as oleoresins containing biopolymers, surface active molecules and small phytochemicals and to provide control over their composition. Among the four general groups (imidazolium, phosphonium, pyridinium, and ammonium), imidazolium based ILs were widely used for their low viscosity and stability in oxidative and reductive conditions. In addition, they can also provide high affinity for lipids and phenolic molecules as compared to conventional organic solvents, such as ethyl acetate, methanol, and hexane. The objectives of this study are to investigate the combined effects of wet milling (i.e., ball milling) and novel ILs (1-n-Hexyl-3-methylimidazolium chloride, 98% and 1-Ethyl-3-methylimidazolium chloride, 97%) on the on the extraction efficiency of oleoresins from waxy sorghum rich in phenolics and evaluate their yield, composition (protein, lipid, fatty acid, phenolic contents) and structural properties of their dispersions (particle size, zeta potential and FT-IR spectrum) in comparison to conventional solvent extraction (i.e., ethanol and dichloromethane).