Subcritical water extraction with compacted natural calcium carbonate column for the extraction of natural products

Abstract

The aim of this work was to develop subcritical water extraction (SWE) method for the extraction of natural products. The developed system was applied to the extraction of natural products from the rhizomes of A. mutica and Calotropis procera as model samples. The efficiency of the SWE method was compared with Soxhlet extraction method using as model sample in terms of yield amount, extraction time and solvent consumption. The SWE attached with compacted natural calcium carbonate (CNCC) method was found to provide higher yield (49.14%) compared with Soxhlet extraction (33%). Three compounds namely kawain, flavokawain and 1,7-diphenyl-5-hydroxy-6-hepten-3-one (DHH) were extracted from the rhizomes of A. mutica using water as a green solvent employing modified subcritical water extraction technique attached to a CNCC column. The CNCC obtained from sea shells was used as adsorbent material to enhance selectivity and purity of the extract. The extract obtained was used without further purification for quantitative analysis based on standard compounds. In this modified SWE technique, water modified with 6-10% acetonitrile, methanol and ethanol were used as extraction solvent. Dried rhizomes of A. mutica were introduced into the extraction vessel connected to the pump that delivers the extractant which further passes through the CNCC unit. The optimum conditions for this extraction were 160?C as extraction temperature, 7 MPa as extraction pressure, 1.8 mL/min as elution volume flow rate and 30 min as extraction time. It was also noted that 160°C extraction temperature produced reasonable amounts of the products (1.891 g, 54.02%, 1.87 g, 53.42% and 1.63 g, 46.6%) with three modifiers (methanol, acetonitrile and ethanol) under identical optimum conditions. The recoveries of the compounds showed good results especially for kawain. Methanol (10%) achieved high recovery (94.82%) compared to the other modifier ratios. In general, the developed method offers rapid and efficient extraction of natural products with reduced organic solvent usage.