High pressure CO2 extraction.: Fundamentals and applications in the food industry

Supercritical extraction (SFE) is a unit operation that exploits the dissolving power of supercritical fluids (SF) under conditions above their critical temperature and pressure. It is possible to obtain solvent-free extracts using SF and the extraction is faster than using conventional organic solvents. These advantages are due to the high volatility of SF (gases under normal environmental conditions) and improved transport properties (i.e., high diffusivity and low viscosity). When using carbon dioxide (CO2) in particular, moderate-temperature processing and high selectivity towards valuable microconstituents in natural products can be achieved. This article presents a review of transport properties and solubilities in SF, particularly CO2, as well as other underlying factors that are responsible for the kinetics and phase equilibrium in SFE processes. It also describes the selective CO2 extraction of essential oils, pungent principles, carotenoid pigments, antioxidants, antimicrobials, and related substances to be used as ingredients for the food, drug and perfume industries, from spices, herbs and other plant materials. These very important applications are discussed from the point of view of the potential applications of SFE in Latin America. The two most: important commercial applications of SFE in the food industry, namely hop extraction and coffee decaffeination, are reviewed to a limited extent. Some other potential applications briefly described include extraction and fractionation of edible fats and oils, purification of solid matrices, and concentration of fermentation broths, fruit juices and other extracts. In most cases CO2 extracts are compared with counterparts obtained using conventional methods.