Ion-exchange and electrodialysis 161 Alternatively the chemical nature of the adsorbed ions could be used as a basis for classification. Any ionisable component of a foodstuff can potentially be adsorbed on to an ion-exchanger and thus separated The following is an attempt to classify applications in food and biotechnoloy sis of the function of the process Softening Softening of water and other liquids involves the exchange of calcium and magnesium ions for sodium ions attached to a cation exchange resin, e. g R-(Na)2+ Ca(HCO3)2-R-Ca-T+ 2NaHCO The sodium form of the cation exchanger is produced by regenerating with NaCl solution. Apart from the production of softened water for boiler feeds and cleaning of food and processing equipment, softening may be employed to remove calcium from sucrose solutions prior to evaporation(which reduces scaling of heat exchanger surfaces in sugar manufacture), and from wine(which improves stability)(Cristal, 1983) Demineralisation Demineralisation using ion exchange is an established process for water treatment, but over the last 20 years it has been applied to other food streams. Typically the process employs a strong acid cation exchanger followed by a weak or strong base anion exchanger. The cations are exchanged with H ions, e. g 2R"H++CaSO 4>(R")2Ca2++H2SO4 R-H++Na+ Na++HcL and the acids thus produced are fixed with an anion exchanger, e. g R+OH-+HtCl-→RCl+H2O Demineralised cheese whey is desirable for use mainly in infant formulations, but also in many other products such as ice cream, bakery products, confectionery, animal feeds etc The major ions removed from whey are Na*, K, Ca, Mg+, CI", HPO4, citrate and lactate. lon-exchange demineralisation of cheese whey generally employs a strong cation exchanger followed by a weak anion exchanger(Houldsworth, 1976). This can produce more than 90% reduction in salt content, which is necessary for infant formulae. Lower levels of demineralisation, obtained using a by-pass system, may be adequate for other applications. Due to the high salt content of whey, the system must be regenerated after the treatment of 10-15 bed volumes of whey. This is achieved, following rinsing, by the treatment of cation and anion exchangers separately with strong acids and alkalis respectively. Typically a cycle is about 6 h, of which 4 h are required for regeneration, therefore two or three parallel systems may be necessary. The use of recurrent regeneration reduces the consumption of regeneration chemicals Jonsson(1984)described the SMr(Swedish Dairies Association) process for whey demineralisation, in which the whey first enters a weak anion column in which the whey anions are exchanged for HCO3 ions. Following this a weak cation column exchanges theIon-exchange and electrodialysis 16 1 Alternatively the chemical nature of the adsorbed ions could be used as a basis for classification. Any ionisable component of a foodstuff can potentially be adsorbed on to an ion-exchanger and thus separated. The following is an attempt to classify applications in food and biotechnology on the basis of the function of the process. Softening Softening of water and other liquids involves the exchange of calcium and magnesium ions for sodium ions attached to a cation exchange resin, e.g. R-(Na+)2 + Ca(HC03)2 -+ R-Ca2+ + 2NaHC03 The sodium form of the cation exchanger is produced by regenerating with NaCl solution, Apart from the production of softened water for boiler feeds and cleaning of food and processing equipment, softening may be employed to remove calcium from sucrose solutions prior to evaporation (which reduces scaling of heat exchanger surfaces in sugar manufacture), and from wine (which improves stability) (Cristal, 1983). Deminerulisution Demineralisation using ion exchange is an established process for watsr treatment, but over the last 20 years it has been applied to other food streams. Typically the process employs a strong acid cation exchanger followed by a weak or strong base anion exchanger. The cations are exchanged with H+ ions, e.g. 2R-Hf + CaS04 -+ (R-)2Ca2+ + H2S04 R-H' + Na'C1- + R-Na' + H+Cl￾and the acids thus produced are fixed with an anion exchanger, e.g. R'OH- + H'Cl- -+ R'CI- + H20 Demineralised cheese whey is desirable for use mainly in infant formulations, but also in many other products such as ice cream, bakery products, confectionery, animal feeds etc. The major ions removed from whey are Na', K+, Ca2+, Mg2+, C1-, HPO,, citrate and lactate. Ion-exchange demineralisation of cheese whey generally employs a strong cation exchanger followed by a weak anion exchanger (Houldsworth, 1976). This can produce more than 90% reduction in salt content, which is necessary for infant formulae. Lower levels of demineralisation, obtained using a by-pass system, may be adequate for other applications. Due to the high salt content of whey, the system must be regenerated after the treatment of 10-15 bed volumes of whey. This is achieved, following rinsing, by the treatment of cation and anion exchangers separately with strong acids and alkalis respectively. Typically a cycle is about 6 h, of which 4 h are required for regeneration, therefore two or three parallel systems may be necessary. The use of countercurrent regeneration reduces the consumption of regeneration chemicals. Jonsson (1984) described the SMR (Swedish Dairies Association) process for whey demineralisation, in which the whey first enters a weak anion column in which the whey anions are exchanged for HCOT ions. Following this a weak cation column exchanges the