Chitosans depolymerized with the aid of papain and stabilized as glycosylamines

The viscosity of chitosan lactate solutions in the concentration range of interest for practical applications (120-150 g kg-1) was promptly lowered in the presence of papain at pH 3.2 and 25-40 °C. Thermal drying of partially depolymerized chitosan lactate brought about side reactions involving structure alterations, and yielded slightly soluble brilliant brown powders. Full solubility and improved organoleptic properties of the partially depolymerized chitosans were obtained by working up the solutions in such a way as to prevent reactions between the reducing ends and the amino groups, i.e. by incubating the ammonia-precipitated partially depolymerized chitosans at 60 °C under pressure with NH3 and drying at 40 °C. The pale yellow product (low molecular weight chitosan in glycosylamine form) had long shelf life and was promptly soluble in the presence of glycolic, lactic, ascorbic and hydrochloric acid, less promptly with citric acid. Three commercially available low molecular weight chitosans were also examined for comparison.