Preparation And Characterization Of PVA Porous Microcapsules Composed Of Permeabilized Brewer's Yeast Cell Core And Perforated Solid Shell

Permeabilized cells are promising biocatalysts for the synthesis of optically active alcohols. Specifically, excellent results were observed for the bioreduction of different esters of 3-ketobutyric acid. However, when permeabilized cells were reused under the same conditions, the intracellular enzyme activities in permeabilized cells and the production yield of the bioreduction process significantly decreased respectively comparing with the previous batch. Therefore, through immobilization techniques, making it into a new biocatalyst having good enzyme activity, good diffusion characteristic and higher operational stability is very necessary.A large number of supports are available for cell immobilization, such as chitosan, sodium alginate (SA), PVA, etc. that should be none toxicity to cells and show satisfactory mechanical strength and stability. In recent years, PVA has been more widely used than other materials in cell immobilization for its cheap, nontoxic, better mechanical property (high mechanical stability, modulus of elasticity and yield strength), and high wearing coefficient. There are several PVA shaping methods, such as multiple freezing and thawing method, crossing-linking by radiation, glutaraldehyde or boric acid.A new method combined coaxial prilling method and in situ gel corrosion perforation (ISGCP) technique is proposed in this paper to prepare PVA porous microcapsules enclosing permeabilized brewer's yeast cells. The main procedures including the preparation of permeabilized brewer's yeast cell enclosed in polyvinyl alcohol/calcium alginate (PVA/CA) microcapsules by coaxial prilling method and hardening of the microcapsules by freezing and thawing method, followed by in situ gel corrosion perforation in sodium phosphate buffer by liquefy the alginate gel in the microcapsules shell. The tests results showed that the microcapsules formed by 9% polyvinyl alcohol (PVA) with 1.5% sodium alginate (SA) were relatively regular in shape, approximately spherical with smooth surface and about 3-4 mm in diameter and permeabilized brewer's yeast cell were completely enclosed inside solid shell. The amount of surviving microcapsules reached 96% after long-term test at 30°C for 30 days. In addition, the hydrophilic and hydrophobic molecules can fast pass through the solid shell into the core, and the diffusion coefficient of perforated microcapsules was obviously lager than the non-perforated microcapsules. Furthermore, the intracellular alcohol dehydrogenase (ADH) in cells enclosed in the microcapsules retained 82% of it original activity after 30 days.