Alginate chemical stability

Immobilisation of an Acetobacter aceti strain in calcium alginate resulted in improvement of the operational stability, substrate tolerance and specific activity of the cells and 23 g phenylacetic acid was produced within 9 days of fed-batch cultivation in an airlift bioreactor [133]. Lyophilised mycelia of Aspergillus oryzae and Rhizopus oryzae have been shown to efficiently catalyse ester formation with phenylacetic acid and phenylpropanoic acid and different short-chain alkanols in organic solvent media owing to their carboxylesterase activities [134, 135] (Scheme 23.8). For instance, in n-heptane with 35 mM acid and 70 mM alcohol, the formation of ethyl acetate and propylphenyl acetate was less effective (60 and 65% conversion yield) than if alcohols with increased chain lengths were used (1-butanol 85%, 3-methyl-l-butanol 86%, 1-pentanol 91%, 1-hexanol 100%). This effect was explained by a higher chemical affinity of the longer-chain alcohols, which are more hydrophobic, to the solvent. 

Zhu H, Srivastava R, Brown JQ, McShane MJ. Combined physical and chemical immobihzation of glucose oxidase in alginate microspheres improves stability of encapsulation and activity. Bioconjugate Chemistry 2005, 16, 1451-1458. 

Transformations with immobilized enzymes or cells Often the stability of the biocatalyst can be increased by immobilization and many different enzymes and cells have been immobilized by a variety of different methods. The most popular method for the fixation of whole cells is entrapment or encapsulation with calcium alginate. Other natural gels e.g., carrageenan, collagen, chemically-modified natural polymers e.g., cellulose acetate and synthetic gels and polymers e.g., polyacrylamide or polyhydroxyethylmethacrylate can also be used for this type of immobilization. 

Although other water soluble polymers have also been used, viable mammalian cells have been encapsulated most frequently in stabilized calcium alginate. Sun pioneered this process to microencapsulate pancreatic islets (2). The thin calcium alginate/polylysine capsule wall was able to protect the transplanted islets from the immune system of the host rats (chemically induced diabetes) for 2-3 weeks initially and with further refinement for as much as two years (3,4). The feasibility of this approach has been shown in various animals (5-8). The long term success in rats has been questioned, however, because of the problem of pancreas regeneration in chemically induced diabetic animals (9). 

Propylene glycol alginate is an emulsifier, stabilizer, and thickener. Chemically, propylene glycol alginate is an ester of alginic acid, which is derived from kelp. Some of the carboxyl groups are esterified with propylene glycol, some are neutralized with an appropriate alkali (73). Polymeric dispersants based on synthetic polymers are shovm in Table 3.37. 

Szente, L. and J. Szejtli, 1988. Stabilization of flavors by cyclodextrins. In Flavor Encapsulation, S.J. Risch (ed.), pp. 148-157. ACS Symposium Series 370, Washington DC American Chemical Society. Tpnnesen, H.H. and J. Karlsen, 2002. Alginate in drug delivery systems. Drug Dev. Ind. Pharm., 28 621-630. 

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