Subcritical water extraction of mannitol from olive leaves

Subcritical water extraction was investigated as a novel and alternative technology in the food and pharmaceutical industry for the separation of mannitol from olive leaves and its results were compared with those of Soxhlet extraction. The effects of temperature, pressure, and flow rate of water and also momentum and mass transfer dimensionless variables such as Reynolds and Peclet Numbers on extraction yield and equilibrium partition coefficient were investigated. The operating conditions were: 3–11 MPa, 333–423 K, and water flow rates of 3.3E-9–3.3E-8 m3/s. The results revealed that the highest mannitol yield was obtained at 373 K and 5 MPa. However, the extraction of mannitol was not influenced by the variation of flow rate. A mathematical model for mannitol extraction was also developed which predicted the experimental measurements very well. In addition, the results indicated higher extraction yield and lower partition coefficient for the subcritical water extraction in contrast to Soxhlet method.