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Biomedical subjects

M G Felipe

Publications and source records attributed to M G Felipe.

12 recordsLinked to original sources
PubMed2001

Metabolic study of the adaptation of the yeast Candida guilliermondii to sugarcane bagasse hydrolysate.

Batch xylitol production from concentrated sugarcane bagasse hydrolysate by Candida guilliermondii was performed by progressively adapting the cells to the medium. Samples were analyzed to monitor sugar and acetic acid consumption, xylitol, arabitol, ethanol, and carbon dioxide production, as well as cell growth. Both xylitol yield and volumetric productivity remarkably increased with the number of adaptations, demonstrating that the more adapted the cells, the better the capacity of the yeast to reduce xylose to xylitol in hemicellulose hydrolysates. Substrate and product concentrations were used in carbon material balances to study in which way the different carbon sources were utilized by this yeast under microaerobic conditions, as well as to shed light on the effect of the progressive adaptation to the medium on its fermentative activity. Such a theoretical means allowed estimation for the first time of the relative contribution of each medium component to the formation of the main products of this fermentation system.

Adaptation, Physiological↗
PubMed2001

Preliminary kinetic characterization of xylose reductase and xylitol dehydrogenase extracted from Candida guilliermondii FTI 20037 cultivated in sugarcane bagasse hydrolysate for xylitol production.

Candida guilliermondii FTI 20037 was cultured in sugarcane bagasse hydrolysate supplemented with 2.0 g/L of (NH4)2SO4, 0.1 g/L of CaCl2 x 2H2O, and 20.0 g/L of rice bran at 35 degrees C; pH 4.0; agitation of 300 rpm; and aeration of 0.4, 0.6, or 0.8 vvm. The high xylitol production (20.0 g/L) and xylose reductase (XR) activity (658.8 U/mg of protein) occurred at an aeration of 0.4 vvm. Under this condition, the xylitol dehydrogenase (XD) activity was low. The apparent K(M) for XR and XD against substrates and cofactors were as follows: for XR, 6.4 x 10(-2)M (xylose) and 9.5 x 10(-3) mM (NADPH); for XD, 1.6 x 10(-1)M (xylitol) and 9.9 x 10(-2) mM (NAD+). Because XR requires about 10-fold less xylose and cofactor than XD for the condition in which the reaction rate is half of the Vmax, some interference on the overall xylitol production by the yeast could be expected.

Air↗
PubMed2001

Application of factorial design to the study of xylitol production from eucalyptus hemicellulosic hydrolysate.

This study deals with the bioconversion of xylose into xylitol by Candida guilliermondii FTI 20037 using eucalyptus hemicellulosic hydrolysate obtained by acid hydrolysis. The influence of various parameters (ammonium sulfate, rice bran, pH, and xylose concentration) on the production of xylitol was evaluated. The experiments were based on multivariate statistical concepts, with the application of factorial design techniques to identify the most important variables in the process. The levels of these variables were quantified by the response surface methodology, which permitted the establishment of a significant mathematical model with a coefficient determination of R2 = 0.92. The best results (xylitol = 10.0 g/L, yield factor = 0.2 g/g, and productivity = 0.1 g/[L x h]) were attained with hydrolysate containing ammonium sulfate (1.1 g/L), rice bran (5.0 g/L), and xylose (initial concentration of 60.0 g/L), after 72 h of fermentation. The pH of fermentation was adjusted to 8.0 and the inoculum level utilized was 3 g/L.

Ammonium Sulfate↗
PubMed2000

Effects of environmental conditions on xylose reductase and xylitol dehydrogenase production by Candida guilliermondii.

The effects of environmental conditions, namely initial pH (2.5-7.0) and temperature (25 and 35 degrees C), on xylose reductase and xylitol dehydrogenase levels, as well as on xylitol production, were evaluated. Although the fermentative parameter values increased with an increase in pH and temperature (the maximum Yp/s and Qp were 0.75 g/g and 0.95 g/[L.h], respectively, both attained at pH 6.0, 35 degrees C), the highest xylose reductase activities (nearly 900 IU/mg of protein) were observed at an initial pH varying from 4.0 to 6.0. Xylitol dehydrogenase was favored by an increase in both initial pH and temperature of the medium. The highest xylitol dehydrogenase specific activity was attained at pH 6.5 and 35 degrees C (577 IU/mg of protein).

Aldehyde Reductase↗
PubMed2000

Effect of the oxygen transfer coefficient on xylitol production from sugarcane bagasse hydrolysate by continuous stirred-tank reactor fermentation.

The effect of the oxygen transfer coefficient on the production of xylitol by bioconversion of xylose present in sugarcane bagasse hemicellulosic hydrolysate using the yeast Candida guilliermondii was investigated. Continuous cultivation was carried out in a 1.25-L fermentor at 30 degrees C, pH 5.5, 300 rpm, and a dilution rate of 0.03/h, using oxygen transfer coefficients of 10, 20, and 30/h. The results showed that the microbial xylitol production (11 g/L) increased by 108% with the decrease in the oxygen volumetric transfer coefficient from 30 to 20/h. The maximum values of xylitol productivity (0.7 g/[L.h]) and yield (0.58 g/g) were obtained akLa 20/h.

Bioreactors↗
PubMed2000

Effects of initial pH on biological synthesis of xylitol using xylose-rich hydrolysate.

Sugarcane bagasse, an agricultural residue plentiful in Brazil, was utilized for xylitol production by a biotechnological process. A medium fermentation prepared with this xylose-rich biomass at an oxygen transfer volumetric coefficient of 10/h1 and different initial pH values was inoculated with cells of Candida guilliermondii FTI 20037. The maximum values of xylitol and cell volumetric productivities (Qp = 0.56 g/[L.h] and Qx = 0.11 g/[g.h]), xylitol yield factor (YP/S = 0.79 g/g), and xylose uptake rate (qs = 0.197 g/[g.h]) were attained at pH 7.0 without further pH control. The results show that the yeast performance was influenced by the pH, an important bioengineering parameter in this fermentation process.

Biological Transport↗
PubMed1999

A preliminary information about continuous fermentation using cell recycling for improving microbial xylitol production rates(scientific note).

Xylitol is a sugar-alcohol with important technological properties, such as anticariogenicity, low caloric value, and negative dissolution heat. It can be used successfully in food formulations and pharmaceutical industries. Its production is therefore in great demand. Biotechnological xylitol production has several economic advantages in comparison with the conventional process based on the chemical reduction of xylose. The efficiency and the productivity of this fermentation chiefly depends on the microorganism and the process conditions employed. In this article a simple continuous culture with cell recycling was evaluated to enhance the capability of Candida guilliermondii FTI 20037 to produce xylitol. The fermentation was initiated batchwise by directly inoculating the grown seed culture in a 2-L bench-scale fermentor. Continuous feeding was begun at a dilution rate (D) of 0.060/h after the xylose concentration had completely consumed and the cell concentration was about 4.0 g/L. At a dilution rate of 0.060/h the xylitol concentration was about 15 g/L and increased by about 35%, whereas the dilution rate decreased by about 58%. Furthermore, the volumetric productivity, Qp, markedly depended on the dilution rate, diminishing by about 37% as D was changed from 0.060 to 0.025/h. These preliminary results show us that continuous fermentation with cell recycling is a good way to study the xylitol production by xylose-fermenting yeasts.

Journal Article↗
PubMed1998

Adaptation and reutilization of Candida guilliermondii cells for xylitol production in bagasse hydrolysate.

The xylitol productivity increased by about 15% with the use of cells of Candida guilliermondii FTI 20037 previously recycled through four consecutive batch cultures and adapted to the sugar cane bagasse hemicellulosic hydrolysate. Furthermore, the more concentrated the hydrolysate, the more necessary was the adaptation of the cells, owing to the presence of toxic substances at high concentration which inhibited the xylose-xylitol conversion by the yeast.

Candida↗
PubMed1998

Factors that affect the biosynthesis of xylitol by xylose-fermenting yeasts. A review.

Xylitol is a sweetener with important technological properties like anticariogenicity, low caloric value, and negative dissolution heat. Because it can be used successfully in food formulations and pharmaceutical industries, its production is in great demand. Xylitol can be obtained by microbiological process, since many yeasts and filamentous fungi synthesize the xylose reductase enzyme, which catalyses the xylose reduction into xylitol as the first step in the xylose metabolism. The xylitol production by biotechnological means has several economic advantages in comparison with the conventional process based on the chemical reduction of xylose. The efficiency and the productivity of this fermentation chiefly depends upon the microorganism and the process conditions employed. In this mini-review, the most significant upstream parameters on xylitol production by biotechnological process are described.

Biotechnology↗
PubMed1995

Effect of acetic acid on xylose fermentation to xylitol by Candida guilliermondii.

The effect of acetic acid concentration on xylose-fermentation to xylitol by Candida guilliermondii FTI 20037 was evaluated in semisynthetic medium containing different concentrations of the acid. Increasing acetic acid concentration up to 1.0 g/l favored xylitol yield and productivity, with maximum values of 0.82 g/g and 0.57 g/l.h, respectively. The presence of acetic acid reduced cell production at all concentration. Furthermore, acetic acid was assimilated by the yeast together with the sugars and was depleted from the medium at concentrations of less than 3.0 g/l. The ability of this yeast to assimilate acetic acid suggests that these cells act as agents of medium detoxification. This behavior may lead to a viable microbiological process of xylitol production by C. guilliermondii FTI 20037 using xylose-rich lignocellulosic hydrolysates in which acetic acid is commonly present, causing inhibition of fermentative activity.

Acetates↗
PubMedDate not supplied

Aspects of the cell growth of Candida guilliermondii in sugar cane bagasse hydrolysate.

In this work the behavior of the growth of Candida guilliermondii FTI 20037 in sugar cane bagasse hemicellulosic hydrolysate on various oxygen transfer rates was investigated. The yeast was able to grow and produced xylitol at different performance levels. At 1.0 vvm (volume of air per volume of medium per minute) the highest growth with 24.4 g/l was observed, but no xylitol was produced. At aeration rate of 0.5 vvm the growth was lower, but therefore slight amounts of xylitol (xylitol yield factor-Yp/s = 0.15 g/g) were observed. The lowest cell concentration (10.7 g/l) and the highest xylitol yield (Yp/s = 0.46 g/g) was observed when aeration was changed from 0.5 vvm to 0.05 vvm after 14 h.

Aerobiosis↗