Effects of butyric and acetic acids on acetone-butanol formation by Clostridium acetobutylicum.

The actions of butyric and acetic acids on acetone-butanol fermentation are investigated. Production of butyric and acetic acids are controlled by the extracellular concentrations of both acids: acetic acid added to the medium inhibits its own formation but has no effect on butyric acid formation, and added butyric acid inhibits its own formation but not that of acetic acid. The ratio of end metabolites depends upon acetic and butyric acid quantities excreted during the fermentation. In contrast to acetic acid, which specifically increases acetone formation, butyric acid increases both acetone and butanol formations. Acetate and butyrate kinase activities were also examined. Both increase at the start of fermentation and decrease when solvents appear in the medium. Coenzyme A transferase activity is weak in the acidogenic phase and markedly increases in the solvent phase. Acetic and butyric acids appear to be co-substrates. On the basis of these results, a mechanism of acetic and butyric acid pathways, coupled to solvent formation by C. acetobutylicum glucose fermentation is proposed.

[Acetobutylic fermentation: strains and regional raw materials]. / Fermentación acetobutílica: cepas y materias primas regionales.

The purpose of the present work was to show, as a first stage, that it is possible to characterize autochtohnous strains of Clostridium acetobutilicum of a good solvent producing capacity, specially N-butanol, through the utilization of suitable techniques for isolating anaerobic microorganisms. Cassava roots were employed as raw material using suitable culture media and an anaerobic jar of cold catalyst. The fermentative capacity of the strains thus isolated was evaluated against a control strain of Clostridium acetobutilicum. Even though some of the strains showed a greater solvent producing power, most of them showed lower fermentation capacity than the control strain, which could be increased, by applying successive thermic treatments. As a second stage, and due to the low cost production of cassava in the Province of Misiones, we studied its utilization as an acetone-butanol fermentation substrate. Mashes composed of binary mixtures of cassava flour and variable amounts of integral flour maize or soy were treated with selected "starters" of Clostridium acetobutilicum, being further processed according to standardized techniques in order to obtain the already mentioned solvents. Mashes concentration influence was also studied using culture media the composition of which proved to be excellent in all experiments carried out under "static system" conditions. The highest fermentative yields (maximum value recorded: 26,20 g of total solvents, with respect to dry solids), were recorded for mashes obtained from mixtures containing integral maize flour; these showed a higher degree of nutrients utilization than those prepared with integral soy flour.

Diacetyl, acetoin, and acetaldehyde production by mixed-species lactic starter cultures.

Citrate utilization and acetoin, diacetyl, acetaldehyde, and lactic acid production in milk at 21 C by five different mixed-strain starters, containing Streptococcus diacetilactis (D type), Leuconostoc (B type), and S. diacetilactis and Leuconostoc (BD type), were measured. BD and D cultures utilized citrate more rapidly and produced more diacetyl, acetoin, and acetaldehyde than B types. All cultures produced much more acetoin than diacetyl, with the BD and D cultures producing four to five times larger amounts of acetoin than the B cultures. Reduction of diacetyl and acetoin toward the end of the normal incubation period was characteristic of BD and D cultures, whereas a similar reduction of acetaldehyde was characteristic of BD and especially of B cultures. Continued incubation of B cultures beyond 17 h also resulted in reduction of diacetyl and acetoin. Addition of citrate to the milk retarded diacetyl and acetoin reduction. Mn(2+) had no effect on diacetyl production by a BD culture but increased citrate utilization and, as a consequence, caused greater diacetyl destruction in one of the B cultures.

Volatile compounds produced in sterile fish muscle (Sebastes melanops) by Pseudomonas putrefaciens, Pseudomonas fluorescens, and an Achromobacter species.

Volatile compounds produced by Pseudomonas putrefaciens, P. fluorescens, and an Achromobacter species in sterile fish muscle (Sebastes melanops) were identified by combined gas-liquid chromatography and mass spectrometry. Compounds produced by P. putrefaciens included methyl mercaptan, dimethyl disulfide, dimethyl trisulfide, 3-methyl-1-butanol, and trimethylamine. With the exception of dimethyl trisulfide, the same compounds were produced by an Achromobacter species. Methyl mercaptan and dimethyl disulfide were the major sulfur-containing compounds produced by P. fluorescens.

Volatile compounds produced in sterile fish muscle (Sebastes melanops) by Pseudomonas perolens.

Volatile compounds produced by Pseudomonas perolens ATCC 10757 in sterile fish muscle (Sebastes melanops) were identified by combined gas-liquid chromatography and mass spectrometry. Compounds positively identified included methyl mercaptan, dimethyl disulfide, dimethyl trisulfide, 3-methyl-1-butanol, butanone, and 2-methoxy-3-isopropylpyrazine. Compounds tentatively identified included 1-penten-3-ol and 2-methoxy-3-sec-butylpyrazine. The substituted pyrazine derivative 2-methoxy-3-isopropylpyrazine was primarily responsible for the musty, potato-like odor produced by P. perolens.