Xylitol, as an alternative low calorie sweetener is well accepted in formulations of various confectioneries and healthcare products. Worldwide it is industrially produced by catalytic hydrogenation of pure d-xylose solution under high temperature and pressure. Biotechnological xylitol production is a potentially attractive replacement for chemical process, as it occurs under much milder process conditions and can be based on sugar mixtures derived from low-cost industrial and agri-waste. However, microbial fermentation route of xylitol production is not so far practiced industrially. This review highlights the challenges and prospects of biotechnological xylitol production considering possible genetic modifications of fermenting microorganisms and various aspects of industrial bioprocessing and product downstreaming.

Several efforts have been made during the last three decades to develop successful lignocellulose-based technologies for the production of fuels and chemicals. However, such technologies still seemed to be emerging, because of the high technical risks involved and huge capital investments. This paper describes a holistic approach toward utilization of sugar cane bagasse as lignocellulosic feedstock into fuel (ethanol), chemical (furfural), and energy (electricity), using a biorefinery approach instead of co-generation. The proposed scheme could be integrated with existing sugar or paper mills, where the availability of biomass feedstock is in abundance. Fermentable sugar components (xylose and glucose) from sugar cane bagasse have been extracted employing acid hydrolysis and enzymatic saccharification. Recovery and reuse of saccharifying enzyme was a major process advantage. The pentose fraction was efficiently utilized for yeast biomass generation and furfural production. High-temperature fermentation of a hexose stream by thermophilic yeast Kluyveromyces sp. IIPE453 (MTCC 5314) with cell recycle produced ethanol with an overall yield of 88% ± 0.05% and a productivity of 0.76 ± 0.02 g/L h–1. A complete material balance on two consecutive process cycles, each starting with 1 kg of feedstock, resulted in an overall yield of 366 mL of ethanol, 149 g of furfural, and 0.30 kW of electricity.

Ethanol production from sugarcane bagasse pith hydrolysate by thermotolerant yeast Kluyveromyces sp. IIPE453 was analyzed using response surface methodology. Variables such as Substrate Concentration, pH, fermentation time and Na2HPO4 concentration were found to influence ethanol production significantly. In a batch fermentation, optimization of key process variables resulted in maximum ethanol concentration of 17.44 g/L which was 88% of the theoretical with specific productivity of 0.36 g/L/h.

This study is aimed at assessing the keratinase production related to industrial detergent applications from a newly isolated Bacillus cereus IIPK35. The production was optimized through submerged fermentation by a one-variable-at-a-time method, followed by the response surface methodology, using waste chicken feathers as a carbon source and resulted in a 5-fold increase in keratinase production in 48 h (103.79 U/mL) when supplemented with 1.43% w/v feather and other nutrients. Time-course study of 120 h revealed a direct relationship among microbial growth, feather degradation, sulfite generation, production of keratinase, oligopeptide, and total protein. The sulfite generation in the culture filtrate suggested the possible sulfur mineralization by disulfide reductase produced by IIPK35. At optimized conditions, cell free fermented broth was enriched with 12 amino acids copiously: threonine (8.52 μg/mL), serine (7.55 μg/mL), and phenylalanine (7.13 μg/mL). Fourier transform infrared analysis reflected the cleavage of peptide bonds associated with feather keratin degradation. IIPK35 keratinase exhibited 79−88% stability and compatibility with commercial detergents and thus appeared to be a promising approach toward laundry detergents. The washing simulation experiment with low supplementation of keratinase combined with detergent demonstrated good destaining of proteinaceous stains without damaging the fabric structure and strength. Thus, the crude keratinase from B. cereus IIPK35 could be considered as a potential bioadditive in detergent formulation.

Optimum utilization of fermentable sugars from lignocellulosic biomass to deliver multiple products under biorefinery concept has been reported in this work. Alcohol fermentation has been carried out with multiple cell recycling of Kluyveromyces marxianus IIPE453. The yeast utilized xylose-rich fraction from acid and steam treated biomass for cell generation and xylitol production with an average yield of 0.315±0.01g/g while the entire glucose rich saccharified fraction had been fermented to ethanol with high productivity of 0.9±0.08g/L/h. A detailed insight into its genome illustrated the strain's complete set of genes associated with sugar transport and metabolism for high-temperature fermentation. A set flocculation proteins were identified that aided in high cell recovery in successive fermentation cycles to achieve alcohols with high productivity. We have brought biomass derived sugars, yeast cell biomass generation, and ethanol and xylitol fermentation in one platform and validated the overall material balance. 2kg sugarcane bagasse yielded 193.4g yeast cell, and with multiple times cell recycling generated 125.56g xylitol and 289.2g ethanol (366mL).

Yeast lipid as single cell oil (SCO) is evaluated as an alternative renewable source of vegetable oils for a biolubricant formulation. The Rhodotorula mucilaginosa IIPL32 yeast strain is cultivated on lignocellulosic pentosans derived from sugarcane bagasse to produce the SCO. The chemical composition and distribution of variable fatty acids in the yeast SCO are characterized by NMR, FTIR, and GC × GC analyses. The high viscosity index and a low pour point of yeast SCO owing to the favorable composition of saturated and unsaturated fatty acids promise its potential as a renewable and environmentally friendly lube base oil. The yeast SCO as lube base oil significantly reduced the coefficient of friction (72%) and wear (24%) compared to those of conventional mineral lube base oil (SN 150). The fatty acids in the yeast SCO formed a good quality tribo-chemical thin film on the engineering surfaces, which not only reduced the friction but also protected the contact interfaces against wear. This study demonstrates that yeast SCO being renewable, biodegradable, and nontoxic, provides favorable physicochemical and tribophysical properties for good quality lubricant formulation and it can be a good alternative to the conventional mineral lube oil-based lubricants.

Single cell oil production from sugarcane bagasse hydrolysate by oleaginous yeast Rhodotorula sp. IIP-33 was analyzed using a two stage statistical design approach based on Response Surface Methodology. Variables like pentose sugar, (NH4)2SO4, KH2PO4, yeast extract, pH and temperature were found to influence lipid production significantly. Under optimized condition in a shake flask, yield of lipid was 2.1199 g with fat coefficient of 7.09 which also resembled ~99% similarity to model predicted lipid production. In this paper we are presenting optimized results for production of non polar lipid which could be later deoxygenated into hydrocarbon. A qualitative analyses of selective lipid samples yielded a varying distribution of free acid ranging from C6 to C18, majoring C16:0, C18:0 and C18:1 under different fermentation conditions.

Present paper describes a process development for fractionation of holocellulose in rice straw into its monomeric sugars employing acid hydrolysis followed by enzymatic saccharification. Rice straw has been hydrolyzed at 140°C and 0.6 % v/v dilute sulfuric acid with 90 min holding time for maximum recovery of pentose monomer (12.52 g xylose/ 100 g biomass). Pentose stream was used for yeast cell biomass generation. Commercial cellulase resulted in 79±0.05 % saccharification efficiency with acid-hydrolyzed biomass. Fermentation of saccharified broth using thermophilic yeast Kluyveromyces sp. IIPE453 (MTCC 5314) with cell recycle produced ethanol with an overall yield and productivity of 93.5±0.05 % and 0.90±0.2 g/L/h, respectively, and with negligible residual sugar in fermentation broth. Lignin-rich residual biomass had a high gross calorific value and could be used as a source of clean gaseous fuel.