Figure 1

Gum arabic is used mainly in food, pharmaceutical, and cosmetic industries due to its unique physiochemical and functional properties (5,6). These functional properties are related directly to the molecular structure. Of particular importance is the amount of the high molecular weight AGP component that is present because it has now been established that this is the component controlling efficiency of emulsification and adhesion (7–9). Gum arabic's role as an emulsifer is achieved as a consequence of its amphiphilic character due to the presence of protein and polysaccharide moieties. It reduces the oil–water interfacial tension, thereby facilitating the disruption of emulsion droplets during homogenization. The peptide moieties (2–3% present in gum arabic) are hydrophobic and strongly adsorb onto the surface of oil droplets, and the polysaccharide chains are hydrophilic and extend out into the solution, which prevents droplet flocculation and coalescence through electrostatic and steric repulsion forces.

The objectives of this article are to demonstrate the application of GPC coupled to three detection systems for the characterization of gum arabic, to provide information about the material now available commercially and the variations present, and, finally, to demonstrate the correlation of arabinogalactan protein component with the emulsification performance.

Methodology

The system consisted of an Agilent 1100 series G1314A UV detector (214 nm, Agilent Technologies, Palo Alto, California), a DAWN EOS MALLS detector (λ=690 nm, Wyatt Technology Corporation, Santa Barbara, California) and an Optilab rEX refractometer (Wyatt Technology Corporation). A Superose 6 10/300GL (Amersham Biosciences, Buckinghamshire, UK) was used with 0.2 M sodium chloride aqueous solution filtered though a 0.22-μm Millipore filter (Millipore, Billerica, Massachusetts) as eluent at flow rate of 0.40 mL/min using a Knauer HPLC pump model K-501 (Berlin, Germany). The gum solution (2 mg/mL) was hydrated overnight. Injection into the GPC column was made with a manual injection value (Rheodyne Model 7725i, supplied by Wyatt Technology, UK) equipped with a 100 μL sample loop. A value of 0.141 mL/g was used for the differential refractive index increment (dn/dc). Astra for Windows software (version 4.90.07, Wyatt Technology Corporation) was used to control data acquisition and the Berry fitting method was used for analysis. The GPC-MALLS system used in this study has been described previously (10,11). Emulsion composition was as follows: gum arabic, 20 w/w%; citric acid, 0.12 w/w%; sodium benzoate, 0.13 w/w%; and MCT, 20 w/w%. Detailed methodology has been described previously (12).