A lag-time model for substrate and product diffusion through hydroxyethylcellulose gels used for immobilization of yeast cells

Abstract

Diffusion models were tested to select the most appropriate model for measuring the diffusion of glucose and ethanol trough hydroxyethylcellulose (HEC) cryogels. The lag-time model was selected as accurate, rapid and reliable for evaluating the diffusivity of the solutes. The diffusion coefficient of glucose through the HEC cryogel loaded with cells was estimated to be 6.9×10-6 cm2/s, while the diffusion coefficient of ethanol had a value of 2.5×10-5 cm2/s. The cells inside the gel matrix were not a barrier for the transport of the solute molecules. The diffusion properties of the cryogel were also examined in a real system. The parameters characterizing the repeated batch fermentation of glucose to ethanol by entrapped Saccharomyces cerevisiae cells gave evidence of very good diffusion properties of the HEC gel.

Keywords

• immobilization
• saccharomyces cerevisiae
• diffusion
• hydroxyethylcellulose
• cryogel