Sequential Process to Valorization of Rambutan Seed Waste by Supercritical CO2-ethanol and Subcritical Water Extractions

Abstract

This work demonstrates the extraction of crude lipid and crude polysaccharide from rambutan (Nephelium lappaceum Linn.) seed using supercritical CO₂ with ethanol as co-solvent (SCE) and subcritical water (SCW) extractions, respectively. As dried rambutan seeds contain 32.48 ± 1.07 g of extractable lipid/100 g dried sample, pre-extraction of 16.65% of the lipid content by a screw pressing machine improved the efficiency of SCE extraction. Moreover, the addition of ethanol as a co-solvent resulted in a fivefold improvement in phenolic compound extraction. The crude lipid extract had a total phenolic content of 163.81 ± 0.47 mg GAE/100 g extract. The SCW extraction was investigated by a Box-Behnken design using extraction yield and total sugar content as responses. The optimal condition was found at temperature range of 150–180°C and extraction time in the range of 15–60 min where both responses were maximized. The solid residue discharged from subcritical water extractor was identified as hydrochar because it contained rich oxygen functional groups. This zero-waste process produced 5.2 kg of SCCO₂-extracted lipid, 16.2 kg of crude polysaccharide, and 37.7 kg of hydrochar from 100 kg of fresh rambutan seed.