Structural Changes Following Industrial Processing of Acacia Gums

This paper reviews the various processing operations starting from gum collection to the commercial end product. Following gum collection the first important step is the drying process. Drying in direct sunlight should be avoided and gradual drying in the shade is recommended. Fresh gum is often called “green gum” which is characterised by high moisture content and less arabinogalactan protein (AGP) fraction compared to a gum which has been stored over a period of time. Subsequent storage conditions can greatly influence the gum quality. The next steps are the kibbling and milling operations. The temperature rise during this process should be controlled to avoid aggregation of the proteinaceous material. This can also affect the quality, since the molecular weight increases as a function of the heat generated. The next step is the dissolution process, when the gum can be modified by the temperature and energy applied to the aqueous solution as a result of foaming. Finally spray-drying operation can result in significant changes to the gum. A 10 to 20% increase in the molecular weight can be caused by this process, but can be considerably higher depending on the way the process is conducted. The dissolution and subsequent stages, particularly the pasteurisation conditions and residence time in the spray-drying tower can contribute to these molecular changes. The current practice employed during spray-drying results in the aggregation of the proteinaceous component and reduces its hydrophobic character due to unfolding of the protein. Consequently, the reduction of the hydrophobic character greatly affects the functionality and the ability of the proteinaceous components to adsorb onto an oil droplet. The GPC-MALLS technique and direct emulsification measurements are used to identify the effect of the various processing conditions outlined above. Significant too is the variation in soil type, rainfall and other environmental factors, which are responsible for the variation in gum quality as for other crops. To address this variation we propose a practical traceability system to identify the origin of the gum and subsequent treatment.