Purification of Xylitol from Fermented Hemicellulosic Hydrolyzate Using Liquid–Liquid Extraction and Precipitation Techniques

Separation of bio-products by liquid–liquid extraction

Solvent extraction one of the oldest approaches of separation known, remains one of the most well-known methods operating on an industrial scale. With the availability of variety of solvents as well as commercial equipment, liquid–liquid extractions finds applications in fields like chemicals and bio-products, food, polymer, pharmaceutical industry etc. Liquid–liquid extraction process is particularly suitable for biorefinery process (through conversion using microorganisms), featuring mild operational conditions and ease of control of process. The principles, types, equipment and applications of liquid–liquid extraction for bioproducts are discussed. Currently various intensification techniques are being applied in the field of liquid–liquid extraction for improving the process efficiency like hybrid processes, reactive extraction, use of ionic liquids etc, which are gaining importance due to the cost associated with the downstream processing of the fermentation products (20–50% of total production cost).

Process scale-up of an efficient acid-catalyzed steam pretreatment of rice straw for xylitol production by C. Tropicalis MTCC 6192

The present study focuses on operational parameters for the efficient acid catalyzed rice straw pretreatment process for xylitol production. 75.77 % xylose yield was attained when the 24 h presoaked rice straw (≤10 mm or ≤ 15 mm) in 1.5 % (v/v) H₂SO₄ was pretreated in the same reactor at 121 °C for 30 min. Neutralization with barium hydroxide produced insoluble salt and noticeably reduced HMF and furfurals. Xylitol yield of 0.6 g/g of xylose, was achieved by fermenting rice straw hydrolysate medium with C. tropicalis MTCC 6192. This two-step process of production of xylitol from xylose rich hydrolysate is much simpler and produced minimal inhibitors including organic acids such as acetic acid. This process is modified for upscaling at optimized parameters and will simultaneously minimize the pollution problem caused by rice straw and is also promising for commercial scale.

Techno-economic and environmental assessment of biogas production from banana peel (Musa paradisiaca) in a biorefinery concept

Two scenarios for the biogas production using Banana Peel as raw material were evaluated. The first scenario involves the stand-alone production of biogas and the second scenario includes the biogas production together with other products under biorefinery concept. In both scenarios, the influence of the production scale on the process economy was assessed and feasibility limits were defined. For this purpose, the mass and energy balances were established using the software Aspen Plus along with kinetic models reported in the literature. The economic and environmental analysis of the process was performed considering Colombian economic conditions. As a result, it was found that different process scales showed great potential for biogas production. Thus, plants with greater capacity have a greater economic benefit than those with lower capacity. However, this benefit leads to high-energy consumption and greater environmental impact.

Development of a transformation system for gene knock-out in the flavinogenic yeast Pichia guilliermondii

Pichia guilliermondii is a representative of a yeast species, all of which over-synthesize riboflavin in response to iron deprivation. Molecular genetic studies in this yeast species have been hampered by a lack of strain-specific tools for gene manipulation. Stable P. guilliermondii ura3 mutants were selected on the basis of 5'-fluoroorotic acid resistance. Plasmid carrying Saccharomyces cerevisiae URA3 gene transformed the mutant strains to prototrophy with a low efficiency. Substitution of a single leucine codon CUG by another leucine codon CUC in the URA3 gene increased the efficiency of transformation 100 fold. Deletion cassettes for the RIB1 and RIB7 genes, coding for GTP cyclohydrolase and riboflavin synthase, respectively, were constructed using the modified URA3 gene and subsequently introduced into a P. guilliermondii ura3 strain. Site-specific integrants were identified by selection for the Rib(-) Ura(+) phenotype and confirmed by PCR analysis. Transformation of the P. guilliermondii ura3 strain was performed using electroporation, spheroplasting or lithium acetate treatment. Only the lithium acetate transformation procedure provided selection of uracil prototrophic, riboflavin deficient recombinant strains. Depending on the type of cassette, efficiency of site-specific integration was 0.1% and 3-12% in the case of the RIB1 and RIB7 genes, respectively. We suggest that the presence of the ARS element adjacent to the 3' end of the RIB1 gene significantly reduced the frequency of homologous recombination. Efficient gene deletion in P. guilliermondii can be achieved using the modified URA3 gene of S. cerevisiae flanked by 0.8-0.9 kb sequences homologous to the target gene.