Alcohol Fermentation and Biomass formation from xylose, glucose and hydrolysate by selected yeast species

Abstract

Fermentation of worts from wood material and other sources of carbon was conducted at 26, 32 and 34°C using 16 strains of Candida, Kluyveromyces, Pachysolen, Saccharomyces and Pichia. Higher yields of ethanol and biomass were recorded from Candida tropicalis (strains C1 and C3) and Candida shehatae (strain C2). Alcohol yields using xylose as the only source of carbon fermented at 26°C by C2, C1 and C3 were determined as 6.4, 5.2, and 4.7 g/l respectively, while the biomass yields were 4.6, 3.9 and 2.4 g/l respectively for the same strains at the same temperature. Organisms that recorded higher values of biomass from xylose included: Kluyveromyces marxianus (K3) (8.0 g/l), Pichia stipitis (A1) (7.9 g/l), Saccharomyces cerevisiae (LB-7) (6.8 g/l) and Kluyveromyces marxianus (K7) (5.4 g/l). Another strain that registered higher concentrations of ethanol included Pachysolen tannophilus (5.5 g/l). Fermentation conducted at 34°C recorded higher alcohol values as compared to that which was conducted at 32°C. At 34°C, higher values of alcohol concentrations were recorded from hydrolysate followed by a mixture of glucose and xylose. Highest alcoholic yield of 18 g/l was recorded using industrial hydrolysate fermented at 34°C. K. marxianus (K3) and K. marxianus (K7) showed low rate of growth and utilization of glucose into biomass (economic conversion coefficient of 0.09 and 0.08 respectively), while the fastest rate of growth and utilization of glucose into biomass was recorded by Pa. tannophilus (P1) (coefficient 0.65). Sacch. Cerevisiae (LB-7) was the slowest in growth and utilization of xylose into biomass (economic conversion coefficient of 0.03), while K3 showed fastest utilization of xylose (coefficient 0.76). For the production of ethanol, the fastest growth and assimilation of glucose was recorded by Pa. tannophilus (P1) (coefficient 0.56) followed by C. shehatae (coefficient 0.43), while P. stipitis (A1) recorded the slowest rate with a coefficient of 0.05. This paper addresses the potential for utilizing xylose fermenting yeasts in fermenting pentoses from lignocellulosic materials obtained from saw dust and agricultural based products such as post harvest straws from maize, rice, sorghum, millet and bagasse from the sugar industries.


Key words: wort, hydrolyzate, glucose, xylose, biomass, ethanol, Candida, Pichia, Kluyveromyces and Pachysolen


Journal of Tropical Microbiology and Biotechnology Vol. 1 (1) 2005: 34-42