Abstract
Acacia gum (AG, E414), also called gum Arabic, is an edible dried gummy exudate obtained from the trunk and branches of Acacia Senegal and Acacia Seyal trees. GA biopolymers belong to the arabinogalactan-protein (AGP) family. They are soft, hyperbranched, charged and amphoteric heteropolysaccharides mainly composed of carbohydrates (D-galactose, L-arabinose, L-rhamnose, D-glucuronic acid, and 4-O-methyl-D-glucuronic acid) with a small fraction of proteins and minerals. GA can be defined as a continuum of biopolymers differing by their biochemical, physicochemical and structural properties. AG is unique among the natural gums because of its techno-functional properties. It is widely used in food and non-food industries (pharmaceutical, printing, textile and cosmetic) as a stabilizer, emulsifier, flavoring agent, and surface-finishing agent. Physicochemical properties of AG are partly related to the molecular distribution of AG biopolymers and especially to the content of protein rich-high molar mass biopolymers. AG is highly soluble in water despite the formation of some aggregates. These properties depend on the physiology of trees and the physical treatments applied to AG after its harvest. For instance, AG aggregates can be induced during the processing of raw gums into spray-dried gums. The storage of spray-dried gums under specific physico-chemical conditions could also induce self-assembly of AG biopolymers. Hence, the understanding of the self-assembly mechanism of AG biopolymers under physico-chemical conditions is becoming essential to better control the physicochemical properties of AG and possibly to develop new AG based ingredients. The main objective of this CIFRE PhD is to investigate the impact of processing and storage conditions of AG biopolymers on their structure and physicochemical and properties. The first stage of the project will be devoted to study the self-assembly (kinetic) properties of AG under specific processing conditions in order to control and modulate the formation of AG assemblies. The aggregation mechanism of AG biopolymers will be studied and defined by characterizing the aggregates using biochemical, spectroscopic and microscopic techniques. The second stage of the project will be dedicated to study the physico-chemical properties of the AG assemblies. The colloidal stability of AG aggregates in solution will be investigated according to the solvent physico-chemical conditions. The impact of these environmental modifications on the structure and composition of aggregates will be studied by a combination of biochemical, chromatographic, scattering and microscopic methods. The functional properties of AG aggregates as the hydration, rheological and interfacial properties will be assessed. These different studies will provide new insights about the self-association mechanism of AGPs and generate new functional assemblies based on AGPs from Acacia gum.