Formation of ethanol and higher alcohols by immobilized zymomonas mobilis in continuous culture

Abstract

Cells of Zyrnomonm mobifis ATCC 10988 were immobilized in 1.5% calcium alginate and packed in a column bioreactor for a series of fermentations utilizing 10.0% glucose media with the addition of one of the following amino acids or keto acids: L-leucine, L-isoleucine, L-valine, a-ketoisocaproic acid, a-ketobutyric acid, or a-ketoisovaleric acid. This was done in order to study the rates of production of higher alcohols during ethanolic fermentations at varying dilution rates while under the influence of amino acids or keto acids.Results indicate that the EHRLICH mechanism is operative in Zymomonas sp. a-Ketobutyrate enhanced the production of n-propanol and act-amyl alcohol. a-Ketoisocaproic acid stimulated the production of isoamyl alcohol. a-Ketoisovaleric acid increased the levels of isobutanol. The amino acids also gave rise to their corresponding alcohols but to a far lesser degree than did the keto acids. During high glucose utilization, ethanol yields ranged from 87% to 94% of theoretical with productivity ranging from 60.08 g/l/h in one fermentation (at a dilution rate of 1.35 h-I) to 70.42 g/l/h in another (at a dilution rate of 1.58 h-I). At dilution rates of 1.58 h-', higher alcohol productivity rose to as high as 4,313 mg/l/h in the presence ofa-ketoisocaproic acid, 1,734.49 mg/l/h usinga-ketoisovaleric acid, and 1,618.05 mg/l/h in a-ketobutyric acid. The concomitant production of ethanol and higher alcohols in all of the fermentations indicates that glucose is required for the production of the higher alcohols from their corresponding amino acids or keto acids.

Biochemical pathways generating post-mortem volatile compounds co-detected during forensic ethanol analyses

“…Indicative of the physiological significance of higher alcohol formation are the following two observations: firstly that the metabolism of glucose is needed for their production [81] and secondly that the appearance of fusel alcohol coincided with the formation of ethanol [81,82,94]. The explanation given to this aspect was that in the presence of glucose, more reductive coenzymes were available for the synthesis of higher alcohols from precursors, even though it is possible that some of the higher alcohols were being produced from glucose.…”

“…Several data support the possibility of higher alcohols formation by bacteria from their relevant a-ketoacids by the same pathways followed by yeasts [82,[84][85][86][87][88][89].…”

“…The ''Ehrlich's pathway'' has been considered to be the predominant pathway for 1-propanol formation from its precursor a-ketobutyrate by yeast [80][81][82][83][84].…”