What is chitosan hydrochloride?

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Chitosan is commercially available in different forms, either as pure chitosan (which is insoluble in water) or as different chitosan salts (which may be readily soluble in water). Chitosan salts are formed when chitosan is dissolved in dilute aqueous acids; the free protons present in the acidic solutions bind to the free amino groups of the glucosamine units in chitosan, leading to positive charges on the chitosan polymers and making them water soluble. When the acid used to solubilize chitosan is hydrochloric acid (HCl), the resulting salt is called chitosan hydrochloride; other acids such as acetic acid or lactic acid lead to the formation of other chitosan salts, such as chitosan acetate or chitosan lactate, respectively. These different counter ions (chloride, acetate, lactate, etc.) influence the properties and the stability of the chitosan salts and their solutions. The characteristic of chitosan salts in dry form is that they dissolve directly in pure water. This offers advantages (for example, ease of formulation and processing), but it also entails some disadvantages such as the need to store them under refrigeration; also, films or nanofibers that are directly obtained as chitosan salts, will dissolve readily when in contact with water, unless a neutralization step is added prior to drying. Chitosan hydrochloride has recently been declared as a 'basic substance' by the European Commission so that products containing only this (and possibly other) basic substances can be brought to the market without the need for registration or approval by the authorities. However, the legal consequences of this decision are not entirely clear yet, and interpretations vary between European countries.