Production of 21% (v/v) ethanol by fermentation of very high gravity (VHG) wheat mashes

Summary Very high gravity wheat mashes containing 300 g or more sugares per liter were prepared by enzymatic hydrolysis of starch and fermented with a commercial preparation of active dry yeast. The active dry yeast used in this study was a blend of several strains ofSaccharomyces cerevisiae. The fermentation was carried out at 20°C at different pitching rates (inoculation levels) with and without the addition of yeast extract as nutrient supplement. At a pitching rate of 76 million cells per g of mash an ethanol yield of 20.4% (v/v) was obtained. To achieve this yeast extract must be added to the wheat mash as nutrient supplement. When the pitching rate was raised to 750 million cells per g of mash, the ethanol yield increased to 21.5% (v/v) and no nutrient supplement was required. The efficiency of conversion of sugar to ethanol was 97.6% at the highest pitching rate. This declined slightly with decreasing pitching rate. A high proportion of yeast cells lost viability at high pitching rates. It is suggested that nutrients released from yeast cells that lost viability and lysed, contributed to the high yield of ethanol in the absence of any added nutrients.     

Manganese as a controlling factor in mixed cultures of Lactobacillus plantarum and enterobacteriaceae

Addition of manganese, at levels of 50 ppm, to a liquid growth medium simulating adverse silage conditions had no effect on the growth or on the fermentation pattern of Enterobacter cloacae and Proteus vulgaris. Yet, the manganese strongly enhanced the growth of Lactobacillus plantarum. Co-cultures of L. plantarum and E. cloacae or P. vulgaris were, by addition of manganese ions, significantly altered in the favour of the former. This finding can be of use in mixed cultures where Enterobacteriaceae act as spoiler microorganisms.     

Fermentative products and dark CO2 fixation during germination of seeds of Cicer arietinum

During the germination of Cicer arietinum L. the amounts of ethanol, lactate and malate reached their highest values at 24 hr, the concentration of ethanol being about 4 times that of lactate and twice that of malate. The activities of phosphoenolpyruvate carboxylase and malic enzyme seem to be correlated with the ability of cotyledons to fix CO₂ from NaH¹⁴CO₃ into malate and with the further decrease in this metabolise from 36 hr onwards.     

Computer control of fermentation processes

A review of computer control of fermentation processes is presented. Hardware and software technologies that have been used to implement computer control are discussed. This includes instrumentation, interfacing techniques, computer hardware configurations, data logging and documentation, displays and man-machine interaction, low-level control, back-up and error detection and programming techniques. Advanced control of fermentation processes with the utilization of modern control techniques is also presented. This topic is divided into steady state optimization and dynamic optimization. Finally, on-line estimation of bioreactor parameters for feedback control is presented.     

Trypanosoma cruzi: Responses by cells from infected mice to alloantigens

In unidirectional mixed lymphocyte cultures containing (as responders, stimulators, or regulators) spleen cells from mice infected with Trypanosoma cruzi, alloantigen responses were less than in cultures containing normal spleen cells only. Depletion of plastic adherent cells from infected spleen cells (stimulators or regulators) reversed their inhibitory effect on normal spleen cells (responders); removal of adherent responder cells and/or B lymphocytes did not alter the low alloantigen responses of normal spleen cells (stimulated by infected spleen cells) or infected spleen cells (stimulated by normal spleen cells). Infected spleen cells were effective in regulating mixed lymphocyte cultures only when added at the initiation of the culture. Serum from infected mice suppressed mixed lymphocyte cultures containing responder spleen cells syngeneic to the serum donor if added up to 24 hr after initiation of cultures, whereas the “suppressor serum” had to be present at the initiation of cultures when responder cells were allogeneic to the serum donor. Cultures of infected spleen cells (whole or macrophage enriched) produced a factor which was suppressive when added to mixed lymphocyte cultures containing syngeneic responder cells at initiation. It is proposed that the serum suppressor substance regulates cell-mediated immune responses directly by suppressing the response-potential of cells and indirectly by triggering the release of a factor from adherent splenic cells which induces a hyporesponsive state in T lymphocytes.     

Growth yield and energy generation in anaerobically-grown Campylobacter spec.

An anaerobic continuous culture study was made with Campylobacter spec. to determine growth yields under various growth conditions. The growth media contained 0.1% (w/v) yeast extract as carbon source. When grown in an aspartate-limited culture Y _asp ^max was 4.6. Inclusion of formate in the culture medium hardly affected the true growth yield. The number of ATP equivalents generated in the fumaratereductase system was 0.66 and the Y _ATP ^max was 7.0. In the nitrate reduction with formate 1.7 ATP equivalents were generated, and a YNO _3- ^max of 12.2 was observed. The true growth yield obtained with a mixture of lactate and aspartate was lower than that found with aspartate alone.     

Pyruvate fermentation in Rhodospirillum rubrum and after transfer from aerobic to anaerobic conditions in the dark

The fermentative metabolism of Rhodospirillum rubrum (strain Ha, F₁, S₁) was studied after transfering the cells from aerobic to anaerobic dark culture conditions. Pyruvate was metabolized mainly to acetate and formate, and to a lesser extent to CO₂ and propionate, by all strains. Therefore, pyruvate formate lyase would appear to be the characteristic key enzyme of the dark anaerobic fermentation metabolism in R. rubrum. Strain F₁ and S₁ metabolized the formate further to H₂ and CO₂. It is concluded that this cleavage was catalysed by a formate hydrogen lyase system. Strain Ha was unable to metabolize formate. The cleavage of formate and the synthesis of poly--hydroxy-butyric acid were increased by a low pH value (6.5). Fermentation equations and schemes of the pyruvate metabolism are discussed.     

Preservation of vegetables by microbial activity and radiation

Two locally-produced seasonal vegetables, carrot and patol, were preserved in brine, with and without radiation, with marked changes in their properties as foods and their microbiology. The treated vegetables could be preserved, at optimum salt and irradiation levels, for up to 60 days without becoming unacceptable in terms of appearance, texture, flavour and taste. The optimum salt concentrations for preservation of carrot and patol were 2% (w/v) and 3% (w/v), respectively. The microbial load initially showed an upward trend and then declined after 5 to 10 days of storage. Lactic acid bacteria predominated in treated vegetables.