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Xylitol is gaining great attention in current pharmaceutical markets. Commercial production by chemical hydrogenation of xylose is however associated with several inevitable drawbacks. Biotechnological route of xylitol production is a superior alternative, if performed at a lower process costs. The goal of present study was to evaluate the efficiency of bacterial cellulose-sodium alginate (BC-AG) composite as an immobilization matrix for Candida tropicalisGS18 in the production of xylitol through a repeated batch fermentation of rice straw hemicellulosic hydrolysate. Different concentrations of bacterial cellulose, sodium alginate, and calcium chloride were screened to select the stable composite for immobilization. Comparative studies for xylitol production using adsorbed yeast cells on BC-AG composite and suspended cells in different production media like synthetic, non-detoxified, and detoxified hydrolysate were carried out. BC-AG composite prepared by using 3.0% alginate and bacterial cellulose in 1:1 ratio through cross-linking with 3.0% CaCl2solution was found to be most suitable for cell immobilization. The maximum xylitol yield and productivity obtained from immobilized cells on BC-AG composite in synthetic and detoxified media were 0.67 g/g; 0.70 g/L/h and 0.55 g/g; 0.52 g/L/h, respectively. The composite was successfully used for up to five repeated batch fermentations in synthetic and detoxified hydrolysate media. However, the composite was unstable in the non-detoxified medium. Hence, BC-AG composite was found to be an effective immobilization matrix for bioconversion of xylose into xylitol.

The present study was aimed to evaluate the ability of Meyerozyma guilliermondiiP14 to produce bioethanol from pretreated biomass of giant reed (Arundo donax). The wild yeast was isolated from its natural habitat and identified by phylogenetic analysis. Arundo donaxbiomass was sequentially pretreated by acid and alkali treatments to break the recalcitrant structure. The pretreated biomass was analysed by FTIR spectroscopy and scanning electron microscopy to observe the structural changes in the biomass. Pretreated biomass was then enzymatically saccharified, and the resultant broth was used to produce ethanol by M. guilliermondiiP14. The fermentation parameters such as pH, temperature, composition of media, and agitation rate were optimized prior to saccharified broth-based fermentations. The results of this study revealed that the dual pretreatment of biomass could make 90.56% cellulose accessible for enzymatic attack. Subsequently, saccharification of pretreated biomass with two enzyme variants resulted in conversion efficiency of 85–87%. Fermentation of saccharified broth resulted in 32.89 g/L final ethanol concentration at 72 h. This has corresponded to 0.48 g/g of ethanol yield and 0.456 g/L/h volumetric productivity. M. guilliermondiiis known to utilize both pentose and hexose sugars unlike Saccharomyces cerevisiaewhich makes it a major player in cellulosic ethanol production. This study provides a significant evidence to the information pool of second-generation bioethanol production from unconventional glucose fermenting yeasts.

Ethanol production from a cellulosic biomass has been realized as a potential way for sustainable circular economy. In this effort, pretreatment processes employed for the depolymerization of structural polymers of rice straw are detrimental and expensive. Here, a novel yeast strain Meyerozyma caribbicaM72 was identified from mahua flower. An efficient process using mild sulfuric acid (0.8%) treatment at temperature 160 °C for 10 min, followed by saccharification with the identified novel yeast, was developed for ethanol production from rice straw. The morphological changes in rice straw upon treatment and saccharification were monitored with SEM, FTIR, XRD, and BET. Identified yeast was found to be able to utilize both pentose and hexose sugars of rice straw. Meyerozyma caribbicaM72 from mahua flower was found to produce ethanol to the extent of 24.36 g/L at 32 °C and pH 7 from saccharified hydrolysate of rice straw in 48 h with 8% ethanol tolerance.

Byline: Kulwant. Singh, Rana. Singh, Sundeep. Kaur We report two children with Amyand's hernia, where the appendices along with caecum were found within the left hernial sac, which were operated [...]