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International audience; The effect of enzymatic modification of polysaccharides on the formed supramolecular structures was studied. Gum Arabic and chitosan were modified by covalent grafting of ferulic acid oxidation products so that they could establish new interactions such as π interactions. The stoichiometry of the interaction was studied by ITC measurements, as well as its strength and related thermodynamic parameters. These experiments were supported by Zeta potential and turbidity measurements and optical macroscopy observations. Grafting of phenolic compounds onto the polymers increased their ability to exhibit π-π stacking and π-cation interactions and led to the formation of various supramolecular structures. For native gum Arabic and chitosan assemblies, the stoichiometry value determined by ITC was consistent with optical microscopy, macroscopic observations and Zeta potential (around a molar ratio gum Arabic:chitosan of 3). The structures formed were coacervates. For the modified polymers, the optimal molar ratio determined by Zeta potential measurements (3.27) differed from the one determined by ITC (6.3). This meant the formation aggregates was not only due to electrostatic interactions but also to other type of interactions (new π-π stacking and π-cation interactions). It was concluded that by modifying the polymers, it was possible to control the supramolecular structures formed

The modification of gum Arabic with ferulic acid oxidation products was performed in aqueous medium, at 30 °C and pH 7.5, in the presence of Myceliophthora thermophila laccase as biocatalyst. First, this study aimed to investigate the structures of the oxidation products of ferulic acid that could possibly be covalently grafted onto gum Arabic. HPLC analyses revealed that this reaction produced several oxidation products, whose structures were investigated using LC-MS/MS analyses (liquid chromatography-mass spectrometry with mass fragmentation analyses) and NMR experiments. The chemical structure of one intermediate reaction product was fully elucidated as the 2-(4-hydroxy-3-methoxyphenyl)-4-[(4-hydroxy-3-methoxyphenyl) methylidene] cyclobutane-1, 3-dione, called by the authors cyclobutadiferulone. Secondly, this study aimed to locate the grafting of the oxidation products onto gum Arabic by performing several NMR experiments. This study did not determine how much and specifically which oxidation products were grafted but some of them were undeniably present onto modified gum Arabic, close to the glucuronic acid C5 carbon or close to the galactose C6 carbon.

Gum Arabic is a natural polysaccharide with valuable properties that enable its use in many industrial fields. Nevertheless, its application field may be enlarged to new properties. One way consists of the modification of the polysaccharide through an enzymatic process based on the oxidation of a phenolic compound. This work aims then to study the impact of the presence of ferulic acid oxidation products onto gum Arabic on its properties as its color, thermal properties, rheological and interfacial behaviors. For instance, modified gum Arabic powder underwent a change of color from white to orange and a glass transition was reported contrary to native gum. Though its rheological behavior did not change, its solubility decreased from 42.5 ± 2.6 to 10.6 ± 0.1% w/v. However, the amphiphilic behavior of functionalized gum Arabic seemed to be different from the one of native gum Arabic. For a given concentration, the surface tension of the modified polymer was lower (31.2 ± 0.8 mN m−1 for native gum Arabic against 52.5 ± 2.4 mN m−1 for the modified gum at 1% w/v). Finally, modified gum Arabic presented important antioxidant properties. The modification of gum Arabic with phenolic compounds appeared then as a promising way to produce a polysaccharide with new properties that could enlarge the field of its potential applications and could make it an interesting food ingredient.

The interactions between gum Arabic (GA) and chitosan (CN) in solution have been investigated upon pH (4.5, 5.0 and 5.5) and temperature (5, 25 and 45 °C). Isothermal titration calorimetry (ITC) has been used to determine the thermodynamic parameters involved in the complex coacervation process between these two polymers. Zeta potential, turbidity measurements and optical microscopy were used as complementary methods to have a better understanding of the phenomenon at the origin of the self-assembly. Unlike data already published by authors, concerning the GA-CN coacervation model, a raise in temperature seemed to favor electrostatic interactions. The enthalpy became more favorable upon temperature, a phenomenon probably related to the availability of CN charges. A raise in temperature would lead to a compaction of CN, decreasing its steric hindrance during self-assembly. According to all experiments conducted in this study, the GA/CN interaction optimal molar ratio would be 4:1. However, this optimal ratio changed upon pH-temperature combinations. The results presented in this study should lead to a better understanding of the interactions between charged polymers and in the end, help in their application in the food, pharmaceutical and cosmetic industries.