Quality control of gum arabic : molecular basis and a new screening method

Abstract

Gum arabic (GA) is commonly used as a stabilizer in aroma oil and beverage emulsions due to its amphiphilic character. However, different GA batches exhibit varying levels of functionality, which so far cannot be related to a molecular parameter. Therefore, the aim of our study was to investigate the relationship between the industrial quality of eight selected GA samples and the (macro)molecular structure and functionality of their glycoprotein fractions in detail, to establish a new quality parameter, and to develop a simplified analytical method for a direct quality assessment. Each GA sample was separated into the three major glycoprotein fractions, which were analyzed for their structural and functional properties. GA quality strongly correlated with the amount of arabinogalactan protein (AGP) and its molecular expansion, expressed via the gyration radius. Based on these results, a new quality parameter was defined as the product of AGP content and the volume of AGP molecules. Furthermore, the spatial expansion of AGP showed a strong positive correlation with the rhamnose and glucuronic acid content, identifying both as a marker for the degree of branching and molecular expansion. For the development of a simplified analytical method, the HIC separation was successfully scaled down, enabling a rapid quantitative isolation of AGP and the subsequent determination of the quality parameter with HPSEC-RI/UV/MALLS. By applying the method to 40 GA samples, it was demonstrated that it allows for a fast and reproducible analysis of GA quality. Thus, the developed analytical approach can complement or replace time-consuming emulsion stability tests.