Recovery of Alkali‑Extracted Soluble Fiber from Coconut Pulp by Single‑Step and Sequential Ethanol Precipitation and Characterization of the Products

The alkaline extraction of soluble fiber from coconut pulp using different concentrations of sodium hydroxide (NaOH) was investigated. Extraction by NaOH solution for 2 h at 2 M and 55 °C released a significant amount of soluble fiber from the pulp. The soluble fiber was then recovered by single-step and sequential precipitations with different ethanol concentrations. Single-step precipitation with high ethanol concentration was effective because it produced a higher yield within a shorter time using less solvent and energy than the sequential method. Extraction under the selected condition, followed by filtration, centrifugation, and single-step precipitation using 75% ethanol, resulted in a soluble fiber product and two residue by-products with yields of 26.6%, 40.4%, and 10.6%, respectively. For the soluble fiber, the relative amount of oligosaccharide or saccharide species smaller than DP 15 was 45.5%, while the rest (54.5%) were polysaccharides with DPs from 15 to 312. The fiber was composed mainly of mannose (66.4%), followed by arabinose (15.9%), galactose/xylose (8.6%), glucose (5.7%), and 3.5% unknown. The soluble fiber was readily soluble in water, while residue #1, which remained after filtration, formed a cloudy white soft gel.