chapter  4
- Membrane Applications in Fruit Processing Technologies
Pages 62

Raw fruit juice is turbid, viscous, and dark in color. Apart from lower molecular weight components like sugar, acid, salt, ˜avor, and aroma compounds, it contains signi’cant amounts of macromolecules (100-1000 ppm) such as polysaccharides (pectins, cellulose, hemicellulose, and starch), haze-forming components (suspended solids (SSs), colloidal particles, proteins, and polyphenol), etc. Hence, the juice needs to be clari’ed before its commercial use. Clari’cation involves the removal of such macromolecules. An enzyme treatment of raw juice is usually carried out with enzymes (pectinase and amylase) to reduce the pectic substances and starch content. This enzyme treatment reduces the cloudiness and makes the ’ltration process easier by lowering its viscosity. The enzyme treatment is followed by the addition of ’ning agents such as gelatin, bentonite, etc., which are used to enhance the settling of formed ˜ocs. Then, SSs, colloidal particles, proteins, etc., are removed by conventional ’ltration. Filter aids such as diatomaceous earth or kieselguhr are used to facilitate the ’ltration process. These conventional methods to clarify fruit

4.2.6.9 Gel Layer Model ................................................................ 108 4.2.6.10 Pore-Blocking Model ......................................................... 109

4.3 Concentration of Fruit Juice ......................................................................... 110 4.3.1 Reverse Osmosis ............................................................................... 110

4.3.1.1 Performance of RO Process ............................................... 110 4.3.1.2 Effects of Different Process Parameters on Permeate

Flux and Retention ............................................................. 111 4.3.1.3 Models for Prediction of Permeate Flux ............................ 115

4.3.2 Direct Osmosis Concentration .......................................................... 121 4.3.2.1 Basic Principle ................................................................... 121 4.3.2.2 Performance of the DOC Process ...................................... 121 4.3.2.3 Effect of Nature and Concentration of Osmotic Medium ...... 122 4.3.2.4 Effect of Hydrodynamic Conditions .................................. 123 4.3.2.5 Effect of Membrane Thickness ..........................................124