Bioconversion of barley straw into yeast biomass and alcohol [electronic resource].

Includes references.

Barley straw was examined as a substrate for yeast biomass or ethanol production. Physical and chemical procedures were applied in order to convert the cellulosic fraction of the straw into soluble sugars, mainly glucose, which in turn could be used by a yeast strain as a carbon source. Pulverization and heat treatment (steaming at 121°.c for 1 hour) were carried out in addition to acid or alkali pretreatment using either H2SO4 or NaOH at different concentrations. In this regard, 4%H2SO4 solution was the most effective in hydrolyzing the straw which was indicated by the release of the highest amount of soluble sugars. The supernatant resulted after acid pretreatment was detoxified and neutralized using overliming with different alkali, Ca (OH)2, NaOH, Ba(OH)2, KOH. Among the examined alkaline solutions; Ca (OH)2 was the best. The supernatant was not the suitable substrate in batch fermentation for yeast biomass production using Sacch. cerevisiae 2030, therefore, it was examined for ethanol production using Sacch. cerevisiae 0-14. The highest yield of alcohol (75-78.3 % of the theoretical) did not greatly affected by the yeast (Sacch. cerevisiae 0-14) inocula size; nevertheless, the fermentation period was shortened when batches were inoculated with 10%. The solid cellulosic residues separated after pretreatment were subjected to chemical hydrolysis using different concentrations of NaOH or H2S04 and autoclaved at different temperatures (100, 121, 136°C) for 1 hour. The maximum amount of glucose was recorded with 2% H2S04 solution at 136°C for 1 hour. Production of yeast biomass from glucose, molasses and acid hydrolyzate in 9-hour fed batch fermentations was investigated. The highest yield coefficient (210%) was obtained with glucose while the yield coefficient was decreased to 105% and 80% when yeast was cultivated on molasses or acid hydrolyzate, respectively.

Summary in Arabic.

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