Effect of zinc chloride solution assisted by ultrasound on polysaccharides of spent coffee grounds

Abstract

Spent coffee grounds (SCG) are rich in polysaccharides, which can be recovered and used for various applications. However, the polysaccharides in SCG are not soluble in water, and an alternative non-toxic solvent is required to dissolve the polysaccharides. Zinc chloride aqueous solution is suitable for such a task because it is non-toxic, non-volatile, and can be easily recovered, thus being an environmentally friendly solvent. To evaluate its effects on polysaccharides, the treatment was performed with alkaline hydrogen peroxide to remove condensed phenolics from SCG. Then, the material was dissolved in 53, 60, and 67% ZnCl2 solutions, assisted by ultrasound. Thermal analysis results indicated that ZnCl2 decreased the thermal stability of the samples. However, the sample dissolved in 53% ZnCl2 assisted by ultrasound showed the highest thermal stability amongst the other samples. FT-IR spectra suggested that the zinc chloride solution had reduced the crystallinity of the material, as indicated by XRD data. However, it was not observed that the appearance of peaks indicated changes in the structure of the polysaccharide molecules. The study demonstrated the relevance of understanding the effects of ZnCl2 solution concentration on the dissolution of polysaccharides, which are essential for lignocellulosic materials applications.

Keywords

• Spent coffee grounds
• Zinc chloride
• Ultrasound
• Polysaccharide
• By-products
• Galactomannan