Chitosan in Eucalyptus grandis Pyroligneous Liquor for Agricultural Application: Physicochemical and Structural Characterization During Storage

Pyroligneous liquor and chitosan are natural and biodegradable products from renewable sources. Both present antimicrobial and antioxidant activities and induce resistance in plants, making these products promising to be used as raw material for agricultural inputs. Chitosan, dissolved in distilled pyroligneous liquor (DPL) from Eucalyptus grandis, produces colloidal systems with high ultraviolet absorption and it could be proposed as plant protective coating, based on their intrinsic characteristics. Chitosan undergoes degradation in an acidic environment; therefore, it is necessary to understand the stability of colloidal systems. We evaluated the systems obtained from chitosan and DPL for their physicochemical properties and structural characteristics at storage times at room temperature (20 ± 5 °C) up to 30 months. The colloidal systems presented a Newtonian flow during the storage time evaluated. Posteriorly, the colloidal systems were destabilized and the precipitates (PPT) were analyzed. Phenolic compounds from DPL were attached to the chitosan chains; this result is supported by fluorescence spectroscopy performed with PPT dissolved in non-fluorescent buffer. The PPT were fluorescent with emission maxima changing to higher wavelengths with storage time. The amounts of total phenols attached to polymer chains increased over time. As a result, there is an increase in the absorption of ultraviolet radiation with storage time. The results show that colloidal systems composed by chitosan formed complexes with phenolic compounds from DPL, which are promising for application in agriculture.