Phenolic compound extraction from spent coffee grounds for antioxidant recovery

As the popularity of coffee beverage increases, an upsurge in the amount of solid residue, known as spent coffee ground (SCG), is inevitable. Currently, SCG is disposed of in the form of solid waste. However, there is a considerable amount of some valuable compounds including phenolic compounds in SCG. In this work, SCG was adopted as a natural antioxidant source for recovering phenolic compounds by an extraction method. An aqueous ethanol solvent (30% v/v) was used at different conditions of temperature, extraction time, and liquid/solid ratio. The amounts of phenolic compounds were analyzed by the well-known Folin-Ciocalteu method, and values were expressed as the weight of gallic acid equivalent (GAE). The highest extraction yield (87.3%) was reported at the highs of process variables; temperature=60 °C, extraction time=150 min, and liquid/solid ratio= 50 mL/g, based on a full factorial experimental design. The statistical Student’s t-test applied to the three operating factors revealed that temperature and liquid/solid ratio are more significant than the extraction time. A correlation equation was proposed to quantitatively analyze the effect of the factors on the reduction yield which could be further used to design and optimize the extraction process.