COMPARATIVE STUDY OF THE FERMENTATION OF ARABINOSE AND XYLOSE BY HANSENULA POLYMORPHA

摘要

The use of lignocellulose materials for the production by biochemical processes of chemical productsrnof high value is promising, because these represent an abundant and renewable source of carbohydrates. Thernhemicellulose fraction from these lignocellulose materials can produce hydrolysates rich in pentoses (D-xylose, Darabinose,rnand L-arabinose). On the other hand, Hansenula polymorpha is a non-conventional methylotrophic yeast,rnparticularly suitable for bioalcohols production in fermentation process at high temperatures (over 30℃) due to itsrnthermotolerant nature and enable to ferment these pentoses to xylitol and arabitol. In this work, the fermentation ofrnD-arabinose, L-arabinose and D-xylose has been carried out by H. polymorpha (ATCC 34438) at 30, 40 and 50℃,rnmodifying pH of the culture (3.5, 4.5 and 5.5) and aeration conditions. The xylitol, arabitol and ethanol productionrnhas been studied. Fermenting the three pentoses (D-xylose, D-arabinose and L-arabinose) with H. polymorpha, underrnthe operation conditions that were tested, has showed that xylitol production is favored vs generation of ethanol. Thisrnyeast is able to ferment L-arabinose to arabitol, but it has difficulties fermenting D-arabinose. In both cases, the yieldsrnin arabitol are very low. The best results were obtained at 40℃, pH=4.5 and agitation of 100 rpm, with an initialrnconcentration of 25 kg dm~(-3) of D-xylose, reaching a maximum specific growth rate of 0.097 h~(-1) and a biomassrnvolumetric productivity of 0.024 kg m~(-3) h~(-1). The best results were obtained to temperature of 40℃, pH=4.5 andrnagitation 100 rpm, with an initial concentration of 25 kg dm~(-3) of D-arabinose, reaching a maximum specific growthrnrate of 0.11 h~(-1) and a biomass volumetric productivity of 0.013 kg m~(-3) h~(-1). The best results were obtained torntemperature of 40℃, pH=4.5 and agitation 100 rpm, with an initial concentration of 25 kg dm~(-3) of L-arabinose,rnreaching a maximum specific growth rate of 0.12 h~(-1) and a biomass volumetric productivity of 0.014 kg m~(-3) h~(-1).rnHigher value of xylitol yield was reached at process time (t) of 69 h, Yxy/s = 0.22 g xylitol (g D-xylose)~(-1), at 50℃ andrnpH=4.5. The best value of arabitol yield was reached at process time of 190 h in D-arabinose fermentation, Yar/s =rn0.12 g arabitol (g D-arabinose)~(-1), at 50℃ and pH=4.5. However, when substrate was L-arabinose, the best value ofrnYar/s was reached at process time of 31.50 h, Yar/s = 0.25 g arabitol (g L-arabinose)-1, at 45℃ and pH=3.5. Higherrnvalue of qAr was 0.01 g g~(-1) h~(-1) at t = 45.5 h, and 0.073 g g~(-1) h~(-1) at t = 3 h for D-arabinose and L-arabinose at 40℃ andrnpH=4.5.