A green integrated approach to extract high-value wax and bioactive compounds from sorghum bran via supercritical carbon dioxide

Abstract: This study offers a green, sustainable extraction method for recovering both high-value wax and phenolic compounds in a single procedure from sustainable crops like sorghum. High-value fractions, namely, wax and phenolic compounds, were generated from sorghum bran using a food-grade method based on a sequential pure supercritical carbon dioxide (SC-CO₂) and water-ethanol-modified SC-CO₂ extraction. Sorghum bran consists of high-melting-point coating wax and oxidative-resistant, potential food colorant agents named 3-deoxyanthocyanins unique to sorghum. The current methods to extract these high-value compounds utilize petroleum-based solvents with energy intensive separation steps. Therefore, the goal of this study was to develop an alternative, sustainable food-grade extraction method to obtain both lipophilic and hydrophilic bioactive compounds from sorghum bran using a single-step SC-CO₂ approach.
Ground black sorghum bran was first subjected to neat SC-CO₂ to extract the nonpolar compounds and then water-ethanol-modified SC-CO₂ to separate the polar compounds in a single run. At the optimized conditions (i.e., 30 MPa and 60 °C), the extraction yield of the nonpolar lipid fraction was 6% (w/w). The major fatty acids in the extracted sorghum bran oil were palmitic acid (16:0), oleic acid (C18:1), and linoleic acid (C18:2). The purified wax fractions containing phytosterols showed high melting points of 57-79 °C. The spent sorghum bran was then subjected to water-ethanol-SC-CO₂ ternary solvent complex to extract phenolic compounds, where the total phenolics and flavonoids contents reached up to 1.2 and 0.8 mg/g, respectively.
Grain sorghum is a highly drought-resistant cereal and therefore can play a critical role in adapting to climate change. The expected outcomes of this research include (i) a sustainable source for high-value wax, (ii) health-promoting phenolic extract for developing functional foods, (iii) natural coloring for the food industry, and (iv) a food-grade method to simultaneously extract and fractionate bioactive compounds while eliminating the use of petroleum-based solvents.