Abstract
Acacia gum (E414) is a dried gummy exudate from Acacia senegal and Acacia seyal trees. It is mainly composed of weakly charged, hyperbranched arabinogalactan-proteins (AGPs) and contains about 90% of polysaccharides and from 1-3% of protein and minerals. The protein/polysaccharide duality is the origin of the amphiphilic character of the gum. Thus, Acacia gums are used as a stabilizer and emulsifier for non-food and food applications, in particular with essential oils (mixtures of aroma compounds) in beverages industry. However, the relation between these properties and the nature of the oil received little attention. The objective of this work is to study the mechanisms involved in aroma emulsions stabilized by Acacia gum. A better understanding of the origin of the gum interfacial and emulsifying properties is intended, in order to possibly extend the gum field of application to a wider range of aroma compounds. To this end, the focus is made on the influence of water, and more specifically of aroma - water interactions, on the gum formation mechanism at the oil-water interface and on emulsion stability. The main results showed aroma - water interactions are the driving force of the gum adsorption. Furthermore, the gum adsorbs preferentially at highly hydrophobic interfaces, inducing high oil surface coverage, high interfacial layer elasticity and ability to reduce the interfacial tension. A volumetric adsorption mechanism is proposed based on enhanced volume fluctuations near highly hydrophobic interfaces, favoring the formation of a dehydrated aroma - gum - water interfacial structure. This mechanism is independent of the number of aroma compounds present in the oil phase. Furthermore, preferential adsorption of oil phase less hydrophobic compounds at oil-water interface is demonstrated. Concerning the emulsifying properties, a relationship, depending on the dispersion mechanisms, between the aroma hydrophobicity and the emulsion droplet size is demonstrated. Finally, the aroma hydrophobicity is shown to influence the aging of the emulsion from the first hour of storage.