HYDRATION CHARACTERISTICS OF THE GUM EXUDATE FROM ACACIA-SENEGAL

Using Differential Scanning Calorimetry the interaction of water with the gum exudate from Acacia senegal can be investigated. The first wat er molecules bind strongly to the hydrophilic groups of the cove carbo hydrate structure and are non-freezing. As the water content is increa sed several metastable freezing-bound states can be identified. One tr ansition at similar to 255 K does not change with increasing water con tent. This metastable freezing-bound water state is closely associated with the polysaccharide structure. The transition of the main freezin g-bound state, however, moves towards that of free water with increasi ng water content. This broad transition embraces at least two other me tastable states, which can be recognised by variations in thermal hist ory. There is one freezing-bound state at similar to 268 K and an acco mpanying metastable state which readily converts to free water on heat ing at 323 K, but when left to stand at room temperature this metastab le state re-forms. Overall, A.senegal can be seen to have a structure which effectively binds water. The freezing-bound states do not overla p with free water until similar to 20% solution has formed. From the D elta H value of the transitions it is evident that the binding of wate r is a necessary driving force not only in. the conventional confectio nary applications, but also in emulsification when the protein cove pe rforms the contrasting hydrophobic directive force.