For most applications of alginates, the molar mass (molecular weight) is an important parameter determining the functionality of the alginate for that specific application. Aqueous solutions of alginates are viscous, the observed solution viscosity being dependent on molar mass, concentration of alginate, temperature, and potentially also presence of salts and other compounds in the formulation. Viscosity measurements are often used as a simple measurable parameter of changes in the molar mass of a polymer, and thereby can be used as a stability indicating parameter.
Depolymerization of alginates will occur in solution and in the solid state due to a variety of mechanisms. Smidsrød et al (1963) observed that the presence of oxygen affected the stability of non-purified alginates in solution due to the presence of phenolic reducing substances that gave rise to oxidative-reductive free radical depolymerization (ORD). On the other hand, Holme et al. (2003; 2008) have shown that purified alginates in the solid state and in solution are depolymerized primarily by acid catalyzed hydrolysis and alkaline catalyzed mechanisms. The highest stability was observed in a pH interval of 5 to 8. Increased temperature will increase the rate of depolymerization for all mechanisms mentioned above (Holme et al. 2003; 2008). In vivo data on the kinetics and mechanism of depolymerization of alginates are scarce. There are no mammalian enzymes that are active towards alginates, however, even in mammals, one must expect random depolymerization mechanisms like the ones described above to occur. This document reports on the stability, shelf-life and storage conditions for PRONOVA UP sodium alginate powders.
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