45H-11 |
Xylitol production from sorghum straw hydrolysates by Debaryomyces hansenii var Hansenii NRRL Y-7426 |
A. M. Barrera-Guillén, Dpto. Tecnología de Alimentos, Universidad Autónoma de Tamaulipas, Campus Aztlán, Reynosa - Tamaulipas, Mexico, J. A. Ramírez, Dept. of Food Science & Technology, Univ. Autónoma de Tamaulipas, UAM Reynosa-Aztlán, Reynosa, Tamaulipas, 88700, Mexico, and M. VÁZQUEZ, Department of Analytical Chemistry - Area Food Technology, Universidad de Santiago de Compostela, Escuela Politécnica Superior, Lugo, 27002, Spain. The hydrolysates of sorghum straw are xylose solutions which can be used to make fermentation media for xylitol production. However, the hydrolysates also contain undesired reaction byproducts which can hinder the fermentation. Therefore, the hydrolysates can be detoxified to allow reasonable kinetics in the fermentation stage. Xylitol is a pentitol with high sweetening power, anticariogenic properties. It is used as a food ingredient. This works deals with xylitol production by fermentation of xylose solutions obtained from sorghum straw hydrolysates using the yeast Debaryomyces hansenii var Hansenii NRRL Y-7426. Experimental design were carried out in order to optimize the composition of media in both raw and detoxified hydrolysates. Acid hydrolysis of sorghum straw were carried out under previously optimized conditions (2% H2SO4, 122 ºC, 71 min, solid/liquid ratio of 1/10 g/g). The liquid phase from hydrolysis was neutralized with CaCO3. The hydrolysates were detoxified using activated carbon. The independent variables were yeast extract, malt extract and peptone in the range 0-6 g/L. The fixed variables were time (96 h), agitation (125 rpm) and temperature (26ºC). Batch fermentations were performed in an orbital shaker under microaerobic conditions, using 250 ml Erlenmeyer flasks with 100 ml of fermentation medium. The concentration of xylitol was higher in detoxified hydrolysates than in raw hydrolysates. The nutritional requirements of the yeast was higher using raw hydrolysates than detoxified hydrolysates. The models predicts that 2.78 g xylitol/L can be obtained by supplementation of the xylose solution with 1.6 g yeast extract/L, 0 g malt extract/L and 6 g peptone /L. Using these nutrients, the xylitol yield obtained (0.18 g/g) was in the range of other xylitol producers microorganisms. The results showed that is feasible the application of sorghum straw hydrolysates for the biotechnological production of xylitol. Further studies are needed to increase the concentration of xylitol.
Session 45H, International: General
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