Feasibility Study on Effect of Microwave-Assisted Extraction Method on Physicochemical Characteristic of Sarawak Coffea liberica sp. Pulp Waste

Coffee is one of the most widely consumed beverages around the globe. Its unique aroma, flavor, and stimulating effects have made it an indispensable part of daily life for many individuals. The coffee industry is notably dominated by two species, Coffea arabica and Coffea canephora (Robusta), however, a third species, Coffea liberica, although less common, holds significant potential. The present study aims to advance the usage of Sarawak Coffea liberica sp. for the development of functional products and aids in reducing environmental pollution by utilisation of coffee pulp waste. This study investigates the optimisation of microwave-assisted extraction (MAE) using response surface methodology (RSM) to obtain maximum yield of total phenolic, flavonoid, and carbohydrate content from Sarawak C. liberica sp. pulp. Optimal MAE conditions were found to be a microwave power of 700 W, irradiation time of 180 s, and a solvent-to-feed ratio of 87:1. Besides, the effectiveness of microwave-assisted extraction (MAE) was compared with Soxhlet extraction (SE) and conventional maceration extraction (CME) in this study. Comparison with CME confirmed the efficiency of MAE as it revealed the advantages of higher extraction yield within a shorter time of extraction. No significant difference was observed (p< 0.05) between MAE and SE on the extraction efficiency of TPC, TFC, and TCC. The antioxidant properties of the coffee pulp waste extract were evaluated, with a DPPH scavenging activity assay revealing a dose-dependent antioxidant activity. Maximum inhibition was observed at a concentration of 2.5 mg/mL, indicating the presence of bioactive compounds. However, no antibacterial activity was detected against Escherichia coli and Staphylococcus aureus under the experimental conditions. Characterisation of the extract via Fourier transform-infrared (FTIR) analysis identified the presence of various functional groups associated with carbohydrates, lipids, organic acids, and phenolic compounds. High Performance Liquid Chromatography (HPLC) quantified the caffeine concentration, revealing a concentration of 2.62 ± 0.31 ppm in the liquid extract and 0.05 ± 0.01% (w/w) on a dry basis. This study contributes to understanding the potential of Sarawak C. liberica sp. pulp as a source of bioactive compounds, while also demonstrating the advantages of MAE over traditional extraction methods. Despite the absence of antibacterial activity, the extract exhibited potential antioxidant properties, emphasizing the potential health benefits and applications of coffee by-products