Subcritical Fluid Extraction

Subcritical fluid extraction is an emerging alternative extraction technique exhibiting great potential for recovering bioactive compounds from food materials. It involves the use of a solvent, usually water, at a temperature above ambient boiling point but at a high pressure (within critical point limit) to maintain liquidity. The accompanying modulation of dielectric constant and polarity of the solvent and an increase of diffusivity enhances the extraction of a wide range of hydrophilic/hydrophobic bioactive compounds, such as carotenoids, phenolics, essential fatty acids, dietary fibre, steroids, and other antioxidants of health significance. Factors such as matrix composition of food material, particle size, solvent type, solid-to-solvent ratio, and process conditions influence extraction yield and quality. For its eco-friendliness, high yield and biological activity, low solvent usage, and versatility, subcritical fluid extraction has advantages over conventional extraction methods. This chapter outlines the principle, equipment design, operation parameters, and safety considerations of subcritical fluid extraction, with a focus on recovering bioactive compounds from fruits, vegetables, cereals, legumes, spices, herbs, and other food sources. It also addresses its strengths and challenges from an industrial perspective.