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A mathematical model was developed for the dynamic and static simulation of a continuous ethanol production process in a tower bioreactor packed with yeast cells immobilized in citrus pectin gel. To avoid accumulation of CO₂ gas during the bioprocess, a vertical fixed bed bioreactor with a working volume of 0.245 L, divided into four stages and equipped with external gas–liquid separators was used. The performance of the bioreactor was evaluated through continuous fermentations using feed medium (sugarcane juice) with substrate concentrations of 161.4 and 312.5 g/L, temperature of 30 °C, pH 4.0 and hydraulic residence times of 5 and 6 h. The developed mathematical model takes into account mass flow by convection and dispersion axial, external and internal mass transfer to/within particle, Contois kinetics for cell growth with inhibition terms, cell death, and substrate consumption for cell maintenance. The partial differential equations regarding cell, substrate and product mass balances in the solid and fluid phase were solved by numerical methods. The calculated profiles of state variables in the fluid phase agreed satisfactorily with the experimental data. The diffusional resistances within particles concerning the substrate consumption rate were not significant, resulting in calculated values of the effectiveness factor close to one. Full article

Ganoderma lucidum, a famous medicinal mushroom used worldwide, is a rich source of triterpenoids which, together with polysaccharides, are believed to be the main effective constituents of G. lucidum. With the increase of market demand, the wild resource is facing serious limitations, and the quality of cultivated fruiting bodies can be seriously affected by the availability of wood resources and by cultivation management practices. In the present study, we aimed to develop an alternative way to produce useful triterpenoids from G. lucidum. We cultured the strain using a two-stage liquid culture strategy and investigated the effects of nitrogen limitation, carbon supply, static culture volume and air supply in the static culture stage on the accumulation of five triterpenoids (GA-P, GA-Q, GA-T, GA-S, GA-R). Our results showed that, under optimized condition, the total yield of the five triterpenoids reached 963 mg/L (as determined by HPLC). Among the five triterpenoids, GA-T accounted for about 75% of the total yield. Besides, a bioreactor suitable for fungal liquid static culture with a 10 L extensible plastic bag shaped culture unit was designed and in which the maximum total yield of the five GAs reached 856.8 mg/L, and the GAs content reached 5.99%. Our results demonstrate the potential of industrial application of G. lucidum culture for the production of triterpenoids, especially GA-T. Air supply significantly improved the accumulation of triterpenoids, and this will provide important clues to understand why more triterpenoids are produced in the mycelia mat under static liquid culture conditions. Full article