Toppings alginates

Figure 2. Structural properties of alginate are shown, with the linear array of Haworth structures given at the top, the conformational structure given next, and the effect of calcium on the formation of complexes between two polymeric strands of alginate given at the bottom. The epimerase catalyzed conversion of / ( —4) linked D-mannuronate to a(l—4) linked L-guluronate residues of poly(ManA) to the catenated structure of poly(GulA) and the formation of the eggbox structure upon the complexing of two polymer strands with Ca. (Reproduced with permission from reference 7. Copyright 1988 Elsevier.)...

Recent examples of process improvement have been reported by Davison and Thomson [11] and Kaufman et al. [12]. They studied the simultaneous fermentation and recovery of lactic acid in a biparticle fluidized-bed reactor using L. delbreuckii as the biocatalyst. The immobilized bacterial cells (on calcium alginate beads of 0.7-0.8 mm diameter) were fluidized in the liquid media in a column reactor (see Fig. 1). During fermentation, solid particles of lactic acid adsorbent (polyvinylpyridine resin) are added batchwise to the top of the reactor, and fall countercurrently through the biocatalyst. After the adsorbents have fallen through the reactor, they are recovered and the adsorbed lactic acid is recovered. The adsorbents not only remove acid produced but also effectively maintain the broth pH at optimal levels. The increase in lactic acid production is significant. The reported volumetric productivity of 4.6 g/l/h was a 12-fold increase over the reactor without the adsorbents. 

Fig. 2 Supramolecular natural polymeric hydrogels discussed in this chapter, (a) Chemical structure of the most-repeated sequence in collagen, forming the a-chain that folds in a three-stranded superhelix [135]. These superhelices bundle to fram the collagen fiber, (b) Representative chemical structure of fibroin and the antiparallel p-sheet formation connected by hydrophilic linkers, (c) Chemical structure of alginic acid, cross-linked by calcium ions (highlighted), (d) Left Top view of two a-helixes of keratin forming a coiled coll by hydrophobic interactions. Right Overview of subsequent formation of the fibril. The left part is adapted from [57] with permission of The Royal Society of Chemistry...

FIGURE 14.1.22 Structure and calcium alginate fiber (top) and scanning electron micrograph of apatite formed on the fiber (left). 

Figure 5.50. Examples of drag delivery using hydrogel membranes. Top carbon dioxide gas pressure causes rapture of membrane, controlled by the membrane thickness and amount of CO2 being produced. Bottom drug release from a polysaccharide alginate capsule, facilitated by multivalent/monovalent ion-exchange, controlled by the molecular weight of the alginate and sire of the capsule. Reproduced with permission from Adv. Drug Deliv. Rev. 2002,54, 53.

Creamed latex is made by the use of a creaming agent such as ammonium alginate. The creaming agent helps form a rubber-rich layer at the top of the holding tank. This is a slow process several weeks may be required before the desired concentration is reached in the top layer, which is drawn off for shipment. Creamed latex has a minimum dry rubber content of 62% and is preferred by rubber thread manufacturers because of its good filterability. 

Preparation of Column—Use Pyrex tubes of 2-cm internal diameter. Soak the prepared alginic acid (4 g 50-100 mesh B.S. per column) in water until swelling is complete (about four hours), then pack in suspension into the tubes previously plugged with cotton wool. Allow the alginic acid to settle and place a second plug on top. Wash the columns... 

Figure 6.1 (Top) The schematic of release mechanism of encapsulated substance in the micro/NPs through the pores of hydrogel network and (Bottom) the release of dexamethasone from either (a) free NPs or NPs entrapped within hydrogels with different alginate concentrations (b) 3% and (c) 1%, respectively.

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