Polysaccharide extraction of defatted rambutan seed by hot water and subcritical water extractions

Extraction methods such as hot water, alkali, acidic, enzyme-assisted, microwave-assisted, and subcritical water extractions were employed to crude polysaccharides–complex carbohydrates composed of short and long chains of sugar molecules. The extracted polysaccharides could be used as prebiotic, nutrients for gut microorganisms. In this study, a screw press machine and supercritical CO₂-ethanol extractor were employed to defat rambutan seed before extracted crude polysaccharides. Proximate analysis showed that DRS contained carbohydrates of 61.63 %, fat of 18.80%, protein of 10.04%, crude fiber of 5.79%, and ash of 1.87%. The defatted seed powder was extracted by a hot water extraction (HWE) at 100°C as a reference condition. Subcritical water extraction (SCWE) were performed at 120–160°C and initial pressure of 2 MPa. The sample to water ratio of 1:10 (w/w) and extraction time of 60 min were held constant for both methods. To identify the structure, the crude polysaccharides was purified by membrane dialysis to remove small molecules (less than 3.5 kDa) and then anion exchange column to separate mono- and oligosaccharides. The results show that the gravimetric extraction yield of 13.95 % and total sugar of 6.78 g/100 extract were obtained from HWE. For SCWE, the extraction yields were in the range of 22.96–33.95 %, whilst the total sugar were in the range of 15.44–32.41 g/100 extract. Antioxidant activities of crude polysaccharides were measured by DPPH, NO, and ABTS assays. To ensure the prebiotic properties, amounts of inhibitors such as furfural, 5-hydroxy furfural, and total phenolic content of extracted polysaccharides were examined as well. The results from this study could be used for further research and development in industrial production of prebiotic.