Integrated supercritical fluid extraction and subcritical water hydrolysis for the recovery of bioactive compounds from pressed palm fiber

Abstract

Pressed palm fiber (PPF), a residue obtained from palm oil industry, is a source of bioactive compounds, such as carotenoids, which are used as food additives. It also has cellulose and hemicellulose that can be used to yield fermentable sugars for the production of second generation ethanol. Supercritical fluid extraction (SFE) of pressed palm fiber provides an oil rich in carotenoids while subcritical water hydrolysis (SubWH) produces hydrolysates with high amounts of fermentable sugars. In this work, the effects of pressure (15–30MPa) and temperature (318 and 328K) on SFE of carotenoids were investigated. The SFE extract with highest carotenoid content was obtained at 318K and 15MPa (2.3% d.b., 0.81mg β-carotene/g extract). After the extraction, the influence of process temperature (423–633K), pressure (15 and 25MPa), solvent:feed ratio (120 and 240), and residence time (1.25–5min) on SubWH of the extraction residue was studied. At the temperature of 523K, the highest total reducing sugar yield (11–23g glucose/100g carbohydrate) and the highest biomass conversion (40–97%) were obtained for any pressure and solvent:feed ratio. The highest selectivity for saccharide formation was found at 423K (20–59mol glucose/mol furfural equivalent). Optimal conditions for high saccharide formation and low sugar degradation product in subcritical hydrolysis were obtained at 523K, 15MPa, solvent:feed ratio of 120, residence time of 2.5min with a total reducing sugar yield of 22.9g glucose/100g carbohydrate and a conversion of 84.9%.