Ultrasonic enhancement of xylitol production from sugarcane bagasse using immobilized Candida tropicalis MTCC 184

Bioprocess optimization for enhanced xylitol synthesis by new isolate Meyerozyma caribbica CP02 using rice straw

The present work models the fermentation process parameters of the newly isolated, Meyerozyma caribbica CP02 for enhanced xylitol production and its fermentability study on rice straw hydrolysate. The study examined the impact of each of the process variables by one variable at a time optimization followed by statistical validation. Temperature of 32 °C, pH of 3.5, agitation of 200 rpm, 1.5% (v/v) inoculum, 80 gL-1 initial xylose was optimized. Subsequently, a sequential two-stage agitation approach was adopted for fermentation. At these optimized conditions, xylitol yield of 0.77 gg-1 and 0.64 gg-1 was achieved using media containing commercial and rice straw derived xylose, respectively. For scale up, in 3L batch bioreactor, the highest xylitol yield (0.63 gg-1) was attained at 72 h with rice straw hydrolysate media containing initial xylose (59.48 ± 0.82 gL-1) along with inhibitors (1.55 ± 0.10 gL-1 aliphatic acids, 0.0.048 ± 0.11 gL-1 furans, 0.64 ± 0.23 gL-1 total phenols). The results imply that even under circumstances characterized by an acidic pH and elevated initial xylose level, M. caribbica CP02, as an isolate, displays robustness and shows favorable fermentability of rice straw hydrolysate. Therefore, isolate CP02 has potential to be used in bio-refineries for high yield xylitol production with minimal hydrolysate processing requirements.

Xylitol biosynthesis enhancement by Candida tropicalis via medium, process parameter optimization, and co-substrate supplementation

The present study examines the impact of nitrogen sources (yeast extract, ammonium sulfate peptone, ammonium nitrate, urea, and sodium nitrate), salt solution (0.5 g/L MgSO4, 0.5 g/L KH2PO4, 0.3 g/L CaCl2), trace elements solution (0.1 g/L CuSO4, 0.1 g/L FeSO4, 0.02 g/L MnCl2, 0.02 g/L ZnSO4), operational parameters (temperature, aeration, agitation, initial pH and xylose concentration) and co- substrate supplementation (glucose, fructose, maltose, sucrose, and glycerol) on xylitol biosynthesis by Candida tropicalis ATCC 13803 using synthetic xylose. The significant medium components were identified using the Plackett Burman design followed by central composite designs to obtain the optimal concentration for the critical medium components in shaker flasks. Subsequently, the effect of operational parameters was examined using the One Factor At a Time method, followed by the impact of five co-substrates on xylitol biosynthesis in a 1 L bioreactor. The optimal media components and process parameters are as follows: peptone: 12.68 g/L, yeast extract: 6.62 g/L, salt solution (0.5 g/L MgSO4, 0.5 g/L KH2PO4, and 0.3 g/L CaCl2): 1.23 X (0.62 g/L, 0.62 g/L, and 0.37 g/L respectively), temperature: 30 °C, pH: 6, agitation: 400 rpm, aeration: 1 vvm, and xylose: 50 g/L. Optimization studies resulted in xylitol yield and productivity of 0.71 ± 0.004 g/g and 1.48 ± 0.018 g/L/h, respectively. Glycerol supplementation (2 g/L) further improved xylitol yield (0.83 ± 0.009 g/g) and productivity (1.87 ± 0.020 g/L/h) by 1.66 and 3.12 folds, respectively, higher than the unoptimized conditions thus exhibiting the potential of C. tropicalis ATCC 13803 being used for commercial xylitol production.

Effects of electrospun nanofiber fabrications on immobilization of recombinant Escherichia coli for production of xylitol from glucose

A suitable nanofiber sheet was formulated and developed based on its efficacy in the immobilization of recombinant Escherichia coli (E. coli) to enhance xylitol production. The effects of different types of nanofibers and solvents on cell immobilization and xylitol production were studied. The most applicable nanofiber membrane was selected via preliminary screening of four types of nanofiber membrane, followed by the selection of six different solvents. Polyvinylidene fluoride (PVDF) nanofiber sheet synthesized using dimethylformamide (DMF) solvent was found to be the most suitable carrier for immobilization and xylitol production. The thin, beaded PVDF (DMF) nanofibers were more favourable for microbial adhesion, with the number of immobilized cells as high as 96 × 106 ± 3.0 cfu/ml. The attraction force between positively charged PVDF nanofibers and the negatively charged E. coli indicates that the electrostatic interaction plays a significant role in cell adsorption. The use of DMF has also produced PVDF nanofibers biocatalyst capable of synthesizing the highest xylitol concentration (2.168 g/l) and productivity (0.090 g/l/h) and 55-69% reduction in cell lysis compared with DMSO solvent and free cells. This finding suggests that recombinant E. coli immobilized on nanofibers shows great potential as a whole-cell biocatalyst for xylitol production.

Food-grade xylitol production from corncob biomass with acute oral toxicity studies

Xylitol, a sugar substitute, is widely used in various food formulations and finds a steady global market. In this study, xylitol crystals were produced from corncob by fermentation (as an alternative to the chemical catalytic process) by a GRAS yeast Pichia caribbica MTCC 5703 and characterized in detail for their purity and presence of any possible contaminant that may adversely affect mammalian cell growth and proliferation. The acute and chronic oral toxicity trials demonstrated no gross pathological changes with average weekly weight gain in female Wistar rats at high xylitol loading (LD₅₀ > 10,000 mg/kg body weight). The clinical chemistry analysis supported the evidence of no dose-dependent effect by analyzing blood biochemical parameters. The finding suggests the possible application of the crystals (> 98% purity) as a food-grade ingredient for commercial manufacture pending human trials.

Ultrasonic-Assisted Dual-Alkali Pretreatment and Enzymatic Hydrolysis of Sugarcane Bagasse Followed by Candida tropicalis Fermentation to Produce Xylitol

In this work, the investigation mainly focused on ultrasonic-assisted dual-alkali pretreatment and enzymatic hydrolysis of sugarcane bagasse followed by Candida tropicalis fermentation to produce xylitol. The results showed that the combination of NaOH and ammonia water had the best effect by comparing the effects of the four single-alkali (NaOH, KOH, ammonia water, Ca(OH)₂) and their mixed double-alkali pretreatments on xylose content. Then, the optimal conditions for ultrasonic-assisted pretreatment and enzymatic hydrolysis of sugarcane bagasse were obtained by response surface methodology. When the ratio of NaOH and ammonia water was 2:1, the mixed alkali concentration (v/v) was 17%, the ultrasonic temperature was 45°C, the ultrasonic power was 300 W, and the ultrasonic time was 40 min, the content of xylose reached a maximum of 2.431 g/L. Scanning electron microscopy showed that sugarcane bagasse by ultrasonic-assisted alkali pretreatment aggravated with more folds and furrows. Moreover, the fermentation results showed that the concentration ratio of enzymatic hydrolysate of sugarcane bagasse affected the xylitol yield, and when concentrated three times, the highest yield of xylitol (54.42%) was obtained.

Utilizing yeasts for the conversion of renewable feedstocks to sugar alcohols - a review

Sugar alcohols are widely marketed compounds. They are useful building block chemicals and of particular value as low- or non-calorigenic sweeteners, serving as sugar substitutes in the food industry. To date most sugar alcohols are produced by chemical routes using pure sugars, but a transition towards the use of renewable, non-edible feedstocks is anticipated. Several yeasts are naturally able to convert renewable feedstocks, such as lignocellulosic substrates, glycerol and molasses, into sugar alcohols. These bioconversions often face difficulties to obtain sufficiently high yields and productivities necessary for industrialization. This review provides insight into the most recent studies on utilizing yeasts for the conversion of renewable feedstocks to diverse sugar alcohols, including xylitol, erythritol, mannitol and arabitol. Moreover, metabolic approaches are highlighted that specifically target shortcomings of sugar alcohol production by yeasts from these renewable substrates.

A Technical System for the Large-Scale Application of Metabolites From Paecilomyces variotii SJ1 in Agriculture

Compared with endophytes, metabolites from endophytes (MEs) have great potential in agriculture. However, a technique for industrializing the production of MEs is still scarce. Moreover, the establishment of effective methods for evaluating the quality of MEs is hampered by the fact that some compounds with beneficial effects on crops have not been clearly identified. Herein, a system was established for the production, quality control and application of MEs by using the extract from Paecilomyces variotii SJ1 (ZNC). First, the extraction conditions of ZNC were optimized through response surface methodology, after which each batch (500 L) met the consumption requirements of crops in 7,467 hectares. Then, chromatographic fingerprinting and enzyme-linked immunosorbent assay were applied to evaluate the similarity and specificity of unknown effective components in ZNC, ensuring a similarity of more than 90% and a quantitative accuracy of greater than 99.9% for the products from different batches. Finally, the bioactivity of industrially produced ZNC was evaluated in the field, and it significantly increased the potato yields by 4.4–10.8%. Overall, we have established a practical technical system for the large-scale application of ZNC in agriculture.

Investigations in ultrasound-assisted anticoagulant production by marine Bacillus subtilis ZHX

Anticoagulants are the main drugs for the prevention and treatment of thromboembolism. However, most of the present anticoagulants have shortcomings and novel anticoagulants are in great demand. Marine microorganisms are an important source of new drugs. Therefore, in this study, ultrasound was applied to enhance anticoagulant accumulation by marine Bacillus subtilis ZHX. Ultrasound parameters were optimized by single-factor experiments exploring the effects of ultrasound power, duration, duty cycle and the cell growth phases. The optimum conditions were exponential prophase (5 h) with 25 kHz frequency, 140 W power, and a 40% duty cycle for 5 min. The maximum anticoagulant activity (55.36 U/mL) was 1.73 times that of the control group, and the fermentation time was shortened by 3 h. Under optimal conditions, ultrasound increased the carbon utilization by Bacillus subtilis ZHX without significant changes in morphology, favoring cell growth and anticoagulant production. However, excessive ultrasound caused intracellular damage, which inhibited biomass accumulation, decreasing anticoagulant activity and even leading to cell rupture. This is the first report on the use of ultrasound to enhance anticoagulant production by Bacillus, and it provides useful information for scaling-up the process.