Optimizing bioencapsulation of yeast cells by Aspergillus tubingensis TSIP9 and applications in bioethanol production through repeated-batch fermentation

This study aimed to immobilize yeast cells using filamentous fungi owing to a number of advantages including less chemical usage, spontaneous encapsulation, strong adhesion and biocompatibility. Filamentous fungus, Aspergillus tubingensis TSIP9 could form sphere-shape and packed pellets using either fungal fresh spores or those stored in liquid medium for 6 weeks at 4 °C. The fungus was used to immobilize yeast Saccharomyces cerevisiae FAI via adsorption and co-cultivation methods. Scanning electron microscopy images revealed that the bioencapsulated yeast cells via co-cultivation seemed to be more tightly adhered on fungal mycelia and surrounded by extracellular polymeric substances. The yeast biocapsules also exhibited higher stability and maintained their structural integrity during repeated-batch fermentation while the immobilized yeast cells by adsorption gradually degraded during their repeated uses. The bioethanol production from glucose by yeast biocapsules were in the range of 95–98 g/L with the bioethanol yield of 0.49–0.54 g-ethanol/g-consumed glucose. The yeast biocapsules could produce bioethanol well when using enzymatic hydrolysate of lignocellulosic palm waste, as alternative cheap carbon source, with the comparable bioethanol yield of 0.49 ± 0.17 g-ethanol/g-consumed glucose. The spontaneous and inter-species bioencapsulation show the perspectives as active biocatalysts with high cell retention for repeated uses.