Ultrasound-microwave assisted extraction of natural colorants from sorghum husk with different solvents

Abstract Ultrasound-microwave-assisted (UMA) extraction method with blended solvent 70% ethanol/30% water with HCl significantly improved extraction of biocolorants from sorghum husk. Sorghum is a staple food in many parts of the world. As the demand for the grain soars, there is an equivalent increase in quantity of sorghum husk generated. Sorghum husk is a promising source for natural functional dye. However, the phenolic colorants in sorghum husk are bound to the cell wall and are difficult to extract. This paper is focused on improving the extraction of natural dye from sorghum husk and investigating the effect of the extraction methods and solvents on the dyeing properties of sorghum husk extracts (SHE). UMA extraction method with blended solvent 70% ethanol/30% water with HCl (1 ml HCl per 100 ml) had a SHE yield of 16.7%, which was 3.6 times the yield of 4.6% by conventional shaking (CS) method with water as solvent. SHE extracted by the UMA method had high contents of apigeninidin as well as luteolinidin and higher thermal stabilities than SHE extracted with water. SHE with different solvents produced different shades when dyeing wool and cotton fabrics. SHE by 70% ethanol/30% water with or without HCI had similar dye strength and significantly higher dye strength compared to SHE extracted by water. The dyed wool and cotton fabrics had good colorfastness to laundry, crocking and light. UMA extraction with blended solvent 70% ethanol/30% water with HCI was an efficient method to extract dye from sorghum husk and provided the potential for industrial application. The use of sorghum husk as a source of industrial dye will significantly add value to the sorghum plant and reduce the disposal of sorghum husk.