Ismael M. Mancilha

Utilization of sugar cane bagasse hemicellulosic hydrolyzate by Candida guilliermondii for xylitol production

Abstract Sugar cane bagasse hemicellulosic hydrolyzate from steam explosion was treated by seven different methods in which the pH was altered by bases (including Ca(OH) 2 , CaO and KOH) and H 2 SO 4 . The effectiveness of the treatment was judged by measuring the conversion of the hydrolyzate to xylitol by Candida guilliermondii . The best treatment was found to be the alteration of pH to 10 with Ca(OH) 2 and its subsequent decrease to 6·5 with H 2 SO 4 , since 95% of the original 70 g/liter xylose contained in the hydrolyzate was converted to xylitol with a yield of 0·48 g/g (53% of the theoretical maximum).

Xylitol production by Candida guillermondii as an approach for the utilization of agroindustrial residues

Abstract Different substrates based on hydrolyzed hemicellulosic fractions of agroindustrial residues were used for xylitol production by Candida guilliermondii FTI 20037 under semi-aerobic conditions. Batch fermentation performances were characterized and compared with those attained in a synthetic medium using d -xylose as a major carbon source. For all media tested, simultaneous utilization of hemicellulosic sugars (glucose and xylose) was observed and the highest substrate uptake rate was attained in sugar cane bagasse medium. Increased xylitol concentrations (40 g/litre) were achieved in synthetic and rice straw-media, although the highest xylitol production rate was obtained in sugar cane bagasse hydrolysate. These results show that both hydrolysates can be converted into xylitol with satisfactory yields and productivities.

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

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.

Batch fermentation of xylose for xylitol production in stirred tank bioreactor

Abstract Xylose conversion into xylitol by Candida guilliermondi FTI 20037 was investigated in a stirred tank bioreactor at different stirring rates. Maximal xylitol production (22·2 g litre −1 ) was obtained at 30°C, with an aeration rate of 0·46 vvm using a stirring rate of 300 min −1 ( K L a =10·6 h −1 ). An increase in K L a produced an increase in the consumption of xylose in detriment to xylitol formation. The efficiency of substrate conversion to xylitol was 45% in a medium containing glucose and xylose but increased to 66% when glucose was omitted.

Improvement in xylitol production from sugarcane bagasse hydrolysate achieved by the use of a repeated-batch immobilized cell system.

Candida guilliermondii cells were immobilized in Ca-alginate beads and used for xylitol production from concentrated sugarcane bagasse hydrolysate during five successive fermentation batches, each lasting 48 hours. The bioconversion efficiency of 53.2%, the productivity of 0.50 g/l × h and the final xylitol concentration of 23.8 g/l obtained in the first batch increased to 61.5%, 0.59 g/l × h and 28.4 g/l, respectively, in the other four batches (mean values), with variation coefficients of up to 2.3%.

Bioconversion of rice straw hemicellulose hydrolysate for the production of xylitol

Xylitol production by the yeastCandida guilliermondii was evaluated in a rice straw hemicellulose hydrolysate under different conditions of initial pH and nitrogen source. Xylitol production was significantly affected (p <0.05) by the nitrogen source, pH, and the interaction between these factors. The best yield and productivity were observed at initial pH of 5.3 in medium containing ammonium sulfate as nitrogen source. Under these conditions, the xylitol yield factor (Yp/s) was 0.68 g/g and volumetric productivity (Qp) was 0.51 g/L.h.

Effect of Culture Conditions on Xylitol Production by Candida guilliermondii FTI 20037

Lignocellulosic materials like sugar cane bagasse include about 35% of hemicellulose (1,2). Hemicelluloses consist of polymeric substances, such as xylans and glucomannans, which differ from cellulose in having shorter molecular chains, a homo-or heteropolymeric backbone structure, and branch molecules, like acetic acid and a variety of pentoses and hexoses (3). The use of D-xylose, the main component of xylan, to obtain chemical products has been a challenge in wood chemistry for the last 10 years.

Sugarcane bagasse as raw material and immobilization support for xylitol production

Xylose-to-xylitol bioconversion was performed utilizing Candida guillier-mondii immobilized in sugarcane bagasse and cultured in Erlenmeyer flasks using sugarcane bagasse hydrolysate as the source of xylose. Fermentations were carried out according to a factorial design, and the independent variables considered were treatment, average diameter, and amount of bagasse used as support for cell immobilization. By increasing the amount of support, the xylitol yield decreased, whereas the biomass yield increased. The diameter of the support did not influence xylitol production, and treatment of the bagasse with hexamethylene diamine prior to fermentation resulted in the highest amount of immobilized cells.

Use of Immobilized Candida Yeast Cells for Xylitol Production from Sugarcane Bagasse Hydrolysate

Candida guilliermondii cells were immobilized in Ca-alginate beads and used for xylitol production from concentrated sugarcane bagasse hydrolysate. A full factorial design was employed to determine whether variations in the immobilization conditions would have any effects on the beads, chemical stability and on the xylitol production rates. Duplicate fermentation runs were carried out in 125-mL Erlenmeyer flasks maintained in a rotatory shaker at 30 degrees C and 200 rpm for 72 h. Samples were periodically analyzed to monitor xylose and acetic acid consumption, xylitol production, free cell growth, and bead solubilization. Concentrations of sodium alginate at 20.0 g/L and calcium chloride at 11.0 g/L and bead curing time of 24 h represented the most appropriate immobilization conditions within the range of conditions tested.

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

Abstract 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 performence levels. At 1.0 vvm (volume of air per volume of medium per minute) the highest growth with 24.4 g/g 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.