Extraction of Natural Pigment Gossypol from Defatted Cottonseed Using 2-Propanol-Water Green Solvent, Its Kinetics and Thermodynamic Study

Herein environment-friendly solvent 2-propanol-water (95:5 v/v) acidified with 0.5 M oxalic acid was utilized to extract gossypol, a naturally occurring pigment of cottonseed. This polyphenolic pigment gossypol acts as a toxin to cottonseed oil and protein during processing of cottonseed by imparting a dark colouration. The parameters affecting the solvent extraction process, such as temperature, solvent-to-seed ratio, acid concentration and contact time, were studied and optimized along with evaluation of kinetic and thermodynamic parameters. The gossypol extraction followed pseudo-second-order kinetics and the kinetics mechanism displayed the diffusion of gossypol from solid phase to the liquid phase. The extraction process was internal diffusion controlled, and internal solid diffusion was the rate controlling step. The optimum conditions for extraction of gossypol were obtained experimentally as 0.5 M oxalic acid concentration, temperature of 348 K, solvent-to-seed ratio of 15 and an extraction time of 180 min, exhibiting maximum gossypol extraction of 95.43% under these conditions. The activation energy of extraction was found out to be 6.099 kJ/mol while the gossypol extraction process was found out to be endothermic in nature, viable and increased the degree of randomness of extraction process. 2-Propanol-water solvent proved to be a potent green solvent for extraction of gossypol from cottonseed.