Abstract
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.
Keywords:
Coconut pulp, Soluble fiber, Alkaline extraction, Ethanol precipitation, Molecular structure
