How alginate properties influence in situ internal gelation in crosslinked alginate microcapsules (CLAMs) formed by spray drying

Abstract

Alginates gel rapidly under ambient conditions and have widely documented potential to form protective matrices for sensitive bioactive cargo. Most commonly, alginate gelation occurs via calcium mediated electrostatic crosslinks between the linear polyuronic acid polymers. A recent breakthrough to form crosslinked alginate microcapsules (CLAMs) by in situ gelation during spray drying (“CLAMs process”) has demonstrated applications in protection and controlled delivery of bioactives in food, cosmetics, and agriculture. The extent of crosslinking of alginates in CLAMs impacts the effectiveness of its barrier properties. For example, higher crosslinking extents can improve oxidative stability and limit diffusion of the encapsulated cargo. Crosslinking in CLAMs can be controlled by varying the calcium to alginate ratio; however, the choice of alginates used in the process also influences the ultimate extent of crosslinking. To understand how to select alginates to target crosslinking in CLAMs, we examined the roles of alginate molecular properties. A surprise finding was the formation of alginic acid gelling in the CLAMs that is a consequence of simultaneous and rapid pH reduction and moisture removal that occurs during spray drying. Thus, spray dried CLAMs gelation is due to calcium crosslinking and alginic acid formation, and unlike external gelation methods, is insensitive to the molecular composition of the alginates. The ‘extent of gelation’ of spray dried CLAMs is influenced by the molecular weights of the alginates at saturating calcium concentrations. Alginate viscosity correlates with molecular weight; thus, viscosity is a convenient criterion for selecting commercial alginates to target gelation extent in CLAMs.

Volatile Retention and Enteric Release of d-Limonene by Encapsulation in Complex Coacervated Powders Formed by Spray Drying

“…The root-mean-square end-to-end distance of alginate with an average molecular weight of 28 200 and a high G/M ratio (G/M = 1.8) was calculated as 48 nm . The alginate used in this study of molecular weight of 172 800 ± 458 was approximately 6-fold larger. Taken together, we surmise that the gelatin–alginate matrix formed in this study could be envisioned as multiple flexible, smaller gelatin polymers crosslinking extended alginate polymers.…”

Synthesis of Alginate Nanogels with Polyvalent 3D Transition Metal Cations: Applications in Urease Immobilization

“…A vast majority of studies related to alginate gelation, structure, and application are based on alginate gel particles measurements ranging between >1 mm (macro), 0.2–1000 µm (micro), and <0.2 µm (nano), containing calcium ions as the most frequently used cross-linking agent [ 13 , 14 ]. The structural analysis has revealed that divalent and trivalent cations are able to form a complex with the G-units of two alginate linear polymer chains, forming a cooperative egg-box structure; thereby, two linear chains of polymer are linked by a cross-link [ 15 , 16 , 17 ]. The naturally occurring alginate’s affinity for divalent cations differ in the following order: Pb > Cu > Cd >Ba > Sr > Ca > Co, Ni, Zn > Mn [ 18 , 19 ].…”

“…A vast majority of alginate particles exist as spheres or beads, synthesized by either internal or external gelation [ 16 , 37 , 38 ]. However, the formation of alginate nanogels is less common in comparison with nanoparticles of other synthetic polymers [ 14 ].…”

Chelator Regulation of In Situ Calcium Availability to Enable Spray-Dry Microencapsulation in Cross-Linked Alginates

“…The alginate type and source can impact properties such as particle size and the extent of cross-linking. 13,14 As a process parameter, spray dryer feed viscosities modulated by the alginate source have been shown to impact CLAMs properties. 13,14 In this study, two commercially sourced alginates were compared on the basis of the resulting viscosities when dissolved in water (high-viscosity (HV) and low-viscosity (LV) alginates).…”

“…13,14 As a process parameter, spray dryer feed viscosities modulated by the alginate source have been shown to impact CLAMs properties. 13,14 In this study, two commercially sourced alginates were compared on the basis of the resulting viscosities when dissolved in water (high-viscosity (HV) and low-viscosity (LV) alginates). The HA-CLAMs were water insoluble and exhibited unique release characteristics.…”