Optimization of ultrasound-assisted extraction of bioactive compounds from green coconut shell

Abstract

Coconut is a tropical fruit widely consumed across many countries. In numerous households, green coconut shells account for more than 60% of total waste by volume. These shells are primarily composed of lignin and cellulose—components similar to those found in wood—making them suitable for phytochemical extraction. To analyse these phytochemicals, ultrasound-assisted extraction was performed under varying conditions, including extraction times (10, 20, and 30 minutes), temperatures (30°C, 35°C, and 40°C), and solid-to-solvent ratios (1:10, 1:20, and 1:30). Optimization of the extraction process was achieved using Response Surface Methodology (RSM). Quantitative analysis of the extracts confirmed the presence of bioactive compounds such as phenols, flavonoids, and tannins, all of which contribute to notable antimicrobial and antioxidant activities. The results showed total phenolic content (TPC) ranging from 7.08 to 33.46 mg GAE/g, total flavonoid content (TFC) from 2.09 to 28.46 mg QAE/g, and total tannin content (TTC) from 70.5 to 141.09 mg TAE/g. The antioxidant activity ranged from 49.98% to 66.1%. The antimicrobial activity was also significant, with inhibition zones against E. coli ranging from 3.7 to 9.6 mm and against S. aureus from 5.8 to 11 mm.Fourier-transform infrared (FT-IR) spectroscopy analysis revealed the presence of functional groups such as O-H, C=O, and C-H. Additionally, the optimized conditions for ultrasound-assisted extraction were compared to those of microwave-assisted extraction (300 watts for 2 minutes), and the ultrasound method yielded superior results.