Meyerozyma caribbica Isolated from Vinasse-Irrigated Sugarcane Plantation Soil: A Promising Yeast for Ethanol and Xylitol Production in Biorefineries.

The production of fuels and other industrial products from renewable sources has intensified the search for new substrates or for the expansion of the use of substrates already in use, as well as the search for microorganisms with different metabolic capacities. In the present work, we isolated and tested a yeast from the soil of sugarcane irrigated with vinasse, that is, with high mineral content and acidic pH. The strain of Meyerozyma caribbica URM 8365 was able to ferment glucose, but the use of xylose occurred when some oxygenation was provided. However, some fermentation of xylose to ethanol in oxygen limitation also occurs if glucose was present. This strain was able to produce ethanol from molasses substrate with 76% efficiency, showing its tolerance to possible inhibitors. High ethanol production efficiencies were also observed in acidic hydrolysates of each bagasse, sorghum, and cactus pear biomass. Mixtures of these substrates were tested and the best composition was found for the use of excess plant biomass in supplementation of primary substrates. It was also possible to verify the production of xylitol from xylose when the acetic acid concentration is reduced. Finally, the proposed metabolic model allowed calculating how much of the xylose carbon can be directed to the production of ethanol and/or xylitol in the presence of glucose. With this, it is possible to design an industrial plant that combines the production of ethanol and/or xylitol using combinations of primary substrates with hydrolysates of their biomass.

Production of 1,3-propanediol by Lactobacillus diolivorans from agro-industrial residues and cactus cladode acid hydrolyzate.

This study evaluated the bioproduction of 1,3-propanediol by Lactobacillus diolivorans in the medium based on agro-industrial residues and vegetal biomass substituting the MRS medium components. It was performed on a set of acid treatments and batch fermentations assays with crude glycerol (TCG) from biodiesel production, corn steep liquor (CSL), and cactus cladode hydrolyzate (CCH). Firstly, it was carried out on batch fermentation with different pure glycerol concentrations in MRS medium which was carried out, and the best condition achieved 4.66 g/L and 0.61 g/g of 1,3-PDO production and yield, respectively. Then, the TCG was evaluated, and a discrete increase of 1,3-PDO was observed. The replacement of the MRS medium nutrients by CLS was assessed, at different concentrations, for bacteria growth, and 5% of CLS reproduced the same biomass formation compared to the bacteria growth in MRS medium. It was also added cactus cladode hydrolyzate as the only sugar source, which showed a 1,3-PDO production close to the medium with pure glucose. Finally, a B-complex vitamin was added to the batch fermentation medium composed of TCG, CLS, and CCH, replacing all the costly MRS components. In this medium, the production of 1,3-propanediol was 6.57 g/L with a yield of 0.75 g/g. It means an increment of 29% and 19%, respectively, compared to MRS medium. Therefore, the combination of treated crude glycerol, corn steep liquor, and cactus cladode hydrolyzate has excellent potential for 1,3-PDO production by L. diolivorans.

Enzymatic hydrolysis of cactus pear varieties with high solids loading for bioethanol production.

The optimization of enzymatic hydrolysis, with high solids loading, of two species of cactus pear for bioethanol production was tested evaluating the influence of surfactant Tween 80 and pretreatment with H2O and H2SO4 (1% v/v) (50 °C, 150 rpm, 3 h). XRD and FTIR analyzes were performed. Afterwards, the influence of the factors cellulase (FPU g-1), pectinase (U g-1) and solids load (% w/v), on the hydrolysis of varieties (50 °C, 150 rpm, 48 h), and the fermentation of the optimal point (33 °C, 8 h) were evaluated. The pretreatments and the Tween 80 did not increase the hydrolysis yields and Rotacional Central Compound Design indicated that the pectinase factor was not significant. The best cellulase and solids load conditions were 10 FPU g-1 of biomass and 30% w/v for both species. The fermentation efficiency of hydrolysates for Nopalea cochenillifera and Opuntia ficus-indica were 76.3% and 82.8%, respectively, showing their potential for bioethanol production.

Recycling the liquid fraction of alkaline hydrogen peroxide in the pretreatment of corn stover.

The aim of this study was to evaluate the influence of recycling the liquid fraction of pretreatment with alkaline hydrogen peroxide (AHP) on the hydrolysis of corn stover. Corn stover was pretreated in the traditional condition with 7.5% v/v H2O2. After pretreatment, the solids were separated from the liquid fraction and five successive reuse cycles of the liquid fraction were tested. The solid fraction from pretreatment in each recycle was submitted to enzymatic hydrolysis. The number of recycles had a linear negative effect (R2=0.98) on biomass delignification efficiency and also affected negatively the enzymatic conversion efficiency. Despite the decrease in efficiency after each recycling step, reuse of the liquid fraction leads to reduction in water, H2O2 and NaOH consumption of up to 57.6%, 59.6% and 57.6%, respectively. These findings point to an efficient recycling technology, which may reduce costs and save water.