Comparison and optimization of solvent extraction and microwave assisted extraction of phenolic compounds from spent coffee grounds

Phenolic compounds from spent coffee grounds were extracted by solvent and microwave assisted extraction methods and response surface methodology was used to optimize the process parameters. Experimental conditions such as temperature (20oC, 40oC, 60oC), time (30min, 60min, 90min), and sample mass (0.5g,1.0g,1.5g) for solvent extraction and microwave power (400W,800W, 1200W), extraction time (40s,80s,120s) and sample mass (0.5g,1.0g,1.5g) were considered for microwave assisted extraction. A complete central composite face centered design has been employed to monitor the combined effect of extraction characteristics on total phenolic content, antioxidant activity, DPPH activity and total extraction yield. The results showed that, model was significant (p<0.05) for all the independent variables considered for the extraction systems. The amount of phenolic content extracted was higher in Microwave assisted extraction (MAE) than for the conventional extraction. The optimized results showed that, 60oC temperature, 90min time, 0.5g of sample mass combination gave maximum results with 44.434mg/g of dry extract of phenolic for solvent extraction whereas, 966.34W power, 49.012s time and 0.5g of sample mass extracted 57.49mg/g of dry extract of phenolic compounds from MAE. When compared, with the reduced time of extraction as low as 49.012s (90min for solvent extraction), medium power and less sample, polyphenols extract with high antioxidant activity was achieved using MAE. The presented data could be a reliable guideline for establishing full-scale, sustainable cost-effective and resource-effective industrial process.