Aqueous solutions of glycolic, propionic, or lactic acid in substitution of acetic acid to prepare chitosan dispersions: a study based on rheological and physicochemical properties

Chitosan (CH) is a biopolymer derived from chitin, which is the second most abundant polysaccharide in nature, after cellulose. Their functional groups -NH₂ and -OH can form intermolecular interactions with water and other molecules, enabling a variety of applications for CH. -NH₂ groups become protonated in acidic solutions, causing an increase in electrostatic repulsion between CH chains, which facilitates their dispersion in aqueous media. Aqueous solutions of acetic acid and/or acetates buffers have been used to disperse CH, but may not be adequate for technological applications, espeacially because of the strong flavor this acid confers to formulations. In this study, 0.125; 0.250; 0.500; 0.750 and 1.000 g (100 g)^-1 CH dispersions were prepared in acidic aqueous media (50 mmol L^-1), not only with acetic (AA), but also with glycolic (GA), propionic (PA), or lactic (LA), acid aiming to evaluate the effects of biopolymer concentration and type of organic acid on: electrical conductivity, pH, density and rheological characteristics of dispersions. Moreover, ζ potential values of CH chains dispersed in these acidic aqueous media were assessed. pH, density and consistency index were influenced by the biopolymer concentration, but not by the acid type. At a given biopolymer concentration, ζ potential signs (+) and values suggested that electrostatic interactions between CH chains and counter-anions occurred, regardless of the type of the organic acid. Thus, at least from a physicochemical point of view, GA, PA or LA showed to be suitable to replace AA when preparing dispersions containing from 0.125 to 1.000 g (100 g)^-1 CH for technological purposes, such as thickening or stabilizer in formulated food products.