Microwave-Assisted Extraction of Phenolic Compounds from Spent Coffee Grounds. Process Optimization Applying Design of Experiments

In this study, sustainable technology microwave-assisted extraction (MAE) in association with green solvents was applied to recover phenolic compounds from spent coffee grounds (SCGs). A design of experiments (DOE) was used for process optimization. Initially, a 2(4-1) two level Fractional Factorial Design was used and ratios solvent to solute and ethanol to water were identified as the significant experimental factors. Consequently, Central Composite Design (CCD) was applied to analyze the effects of the significant variables on the response yield, total polyphenols content (TPC), and antioxidant activity (AA) by the DPPH assay method, and quadratic surfaces to optimize those responses were generated. The values of the significant factors of 16.7 (solvent/solute) and 68.9% (ethanol/water) were optimized simultaneously the yield (%) at 6.98 +/- 0.27, TPC (mg GAE/g) at 117.7 +/- 6.1, and AA (mu mol TE/g) at 143.8 +/- 8.6 and were in excellent agreement with those predicted from the CCD model. The variations of the compositions of the lipids, caffeine, pentacyclic diterpenes, and FAME as a function of the dominant factor % ethanol in the solvent mixture were analyzed by applying NMR and GC-FID, and the results obtained confirmed their determinative significance.

Automated summary

In this study, MAE technology with green solvents was used to extract phenolic compounds from SCGs, optimized through DOE and CCD methods. The significant factors and optimized values were identified, leading to successful optimization of yield, TPC, and AA. Analysis of compound compositions confirmed the determinative significance of ethanol percentage in the solvent mixture.