Influence of Microwave and Ultrasound pretreatment on Solvent Extraction of Bio-components from Walnut (Julgans regia L.) Shells

Walnut (Julgans regia L.) shells, an agro-forestry waste, are a rich source of phytochemicals with anti-oxidative and medicinal properties. Whilst recent research efforts focus on waste valorization, the present investigation demonstrates a process to extract and characterize bio-components from physically pretreated walnut shells. Pretreatment was undertaken using microwave irradiation and ultra-sonication with two different solvents (methanol and acetone). The extract obtained was optimized using Response Surface Methodology (RSM). Further, the bio-components in the extract were identified using GCMS and FTIR analyses. Through the experimental runs, it was observed that pretreatment enhanced the total extract yield from the process relative to conventional Soxhlet extraction. As a method of pretreatment, microwave irradiation was found to suit the extraction better than ultra-sonication. In addition, acetone performed better as a solvent than methanol in the bio-components recovery. Relative to conventional Soxhlet extraction, microwave pretreatment allowed for enhanced separation by 4.06 folds for methanol and 5.25 for acetone. The yield was found to be the highest (46 mg/g) while using acetone, when pretreated with microwaves at 180 W for 4 min.