Recovery of chitosan from aqueous acidic solutions by salting-out. Part 2: Use of salts of organic acids

We have previously reported that inorganic salts of the Hofmeister series could be used efficiently to recover chitosan from aqueous acidic solutions. Here, we extended these findings to food-compatible, naturally occurring, salts of tricarboxylic, dicarboxylic and monocarboxylic acids. Trisodium citrate was an efficient salting-out agent of 30 kiloDaltons (kDa) chitosan but was less potent in the case of a 240-kDa and a 70 cP form of the biopolymer dissolved in dilute aqueous HCl or acetic acid. Temperature (4 °C, room temperature or 50 °C) had no appreciable effect. We also showed that trisodium citrate was an efficient salting-out agent of chitosans for molecular sizes of 26,000 Da to ⩾139,000 Da. The sodium salt of dicarboxylic (malic, tartaric, succinic and malonic) acids salted-out 30 kDa chitosan but were generally less efficient in the case of the 240 kDa and 70 cP chitosans, independently of temperature. The sodium salt of monocarboxylic (acetic, lactic and propionic) acids were not efficient salting-out agents of any of the three types of chitosans used here, independently of temperature. The 30 kDa chitosan salted-out with the sodium salts of citric, tartaric, malic and malonic acids was in general soluble in dilute aqueous HCl or dilute aqueous acetic acid. Our data were consistent with the interpretation that some salts of food-compatible tricarboxylic and dicarboxylic acids could be used for salting-out chitosans, taking into account, (1) the efficiency of recovery and (2) the molecular size of the chitosans to be recovered.