Effect of certain environmental factors and radiation on

Amany Badr El-deen Abd El-AzizTitle: Effect of certain environmental factors and radiation on xylitol production from rice straw by yeasts.Three active local yeast strains (Debaryomyces hansenii, Candida shehatae and Candida tropicalis) isolated from different fruits were active for xylitol productions from D-xylose.Different environmental conditions including (shaking speed, temperature, pH, inoculum age and size, different nitrogen sources, aeration and different concentrations of D-xylose) were tested and optimized for increasing the xylitol production by the loca250 g/l of D-xylose in the fermentation medium with the best culture conditions for each isolate increased the xylitol yield for all of them. The local isolate Can. tropicalis gave the best results (160.6g/l) over the other isolates even the standard straBy using different chemical and physical treatments for increasing the D-xylose and decreasing the toxic substances resulted from the hydrolysis of rice straw, the production of xylitol and xylose reductase enzyme increased in comparison with the xylitol High dose level of gamma rays (100 kGy) with diluted sulphuric acid treatment increased the xylitol yields from rice straw hydrolysates to 43.2 and 45.0 g/l out of 63.0 g/l for Can. tropicalis and Can. guilliermondii, respectively