Xylitol production by Candida tropicalis under different statistically optimized growth conditions
Nutritional and environmental conditions of the xylose utilizing yeast Candida tropicalis were optimized on a shake-flask scale using a statistical factorial design to maximize the production of xylitol. Effects of the three growth medium components (rice bran, ammonium sulfate and xylose) on the xylitol production were studied, each at three different levels and the highest xylose to xylitol conversion ratio (57.2%) was achieved on using 20 gl-1 of xylose, 15 gl-1 of rice bran and 1 gl-1 of ammonium sulfate. By maintaining the pH of the growth medium at 5.5 using citrate buffer, the xylose to xylitol conversion ratio was greatly enhanced (93.75%) over the use of or unbuffered growth medium and phosphate buffered (88.3 and 83.8%).The least aeration rate was simulated by 40 ml of the growth medium at 250 ml-1. Erlenmeyer flasks result in maximum xylose to xylitol conversion ratio (98%), by using 25 gl-1 of xylose, while maximum xylitol production (36.25 gl-1) with a conversion ratio of 72.5% was achieved by using 50 gl-1 of xylose.
Key words: xylitol, Candida tropicalis, xylose, yeast, pH, aeration.