| 1. |
- Akerberg, C, et al.
(författare)
-
Modelling the influence of pH, temperature, glucose and lactic acid concentrations on the kinetics of lactic acid production by Lactococcus lactis ssp. lactis ATCC 19435 in whole-wheat flour
- 1998
-
Ingår i: Applied Microbiology and Biotechnology. - : Springer Science and Business Media LLC. - 1432-0614 .- 0175-7598. ; 49:6, s. 682-690
-
Tidskriftsartikel (refereegranskat)abstract
- A kinetic model of the fermentative production of lactic acid from glucose by Lactococcus lactis ssp. lactis ATCC 19435 in whole-wheat flour has been developed. The model consists of terms for substrate and product inhibition as well as for the influence of pH and temperature. Experimental data from fermentation experiments under different physical conditions were used to fit and verify the model. Temperatures above 30 degrees C and pH levels below 6 enhanced the formation of byproducts and D-lactic acid. By-products were formed in the presence of maltose only, whereas D-lactic acid was formed independently of the presence of maltose although the amount formed was greater when maltose was present. The lactic acid productivity was highest between 33 degrees C and 35 degrees C and at pH 6. In the concentration interval studied (up to 180 g l(-1) glucose and 89 g l(-1) lactic acid) simulations showed that both substances were inhibiting. Glucose inhibition was small compared with the inhibition due to lactic acid.
|
|
| 2. |
- Björnsson, Lovisa, et al.
(författare)
-
Effects of support material on the pattern of volatile fatty acid accumulation at overload in anaerobic digestion of semi-solid waste
- 1997
-
Ingår i: Applied Microbiology and Biotechnology. - : Springer Science and Business Media LLC. - 1432-0614 .- 0175-7598. ; 47, s. 640-644
-
Tidskriftsartikel (refereegranskat)abstract
- Anaerobic degradation of a semi-solid waste with a total solids content of 4% particulate matter, much of it insoluble, was investigated in four laboratory-scale reactors. Two of the reactors were equipped with different textile materials for immobilisation of microorganisms, while the other two were used as continuously-stirred-tank reactor references, A constant organic loading rate and hydraulic retention time were used in the start-up period; the hydraulic retention time was then decreased and the effects of this change were monitored. Volatile fatty acid (VFA) concentration and pH were chosen as indicators of the microbial status in the reactors. The reactors with support material showed a greater resistance to overload than did the continuously-stirred-tank reactors. This is in agreement with many studies undertaken on the anaerobic treatment of wastewater. However, no problems with clogging occurred, showing that a support material is also applicable in systems treating waste containing large amounts of insoluble, particulate matter. The pH was comparable to VFA for indicating an approaching process failure. However, the pattern of VFA accumulation was qualitatively different between the reactors with and without support material, Obviously the metabolic pattern of mixed cultures changes when the microorganisms are immobilised.
|
|
| 3. |
- Hofvendahl, Karin, et al.
(författare)
-
Effect of temperature and pH on growth and product formation of Lactococcus lactis ssp. lactis ATCC 19435 growing on maltose
- 1999
-
Ingår i: Applied Microbiology and Biotechnology. - : Springer Science and Business Media LLC. - 1432-0614 .- 0175-7598. ; 51:5, s. 669-672
-
Tidskriftsartikel (refereegranskat)abstract
- Lactococcus lactis ssp. lactis ATCC 19435 is known to produce mixed acids when grown on maltose. A change in fermentation conditions only, elevated temperatures (up to 37 °C) and reduced pH values (down to 5.0) resulted in a shift towards homolactic product formation. This was accompanied by decreased growth rate and cell yield. The results are discussed in terms of redox balance and maintenance, and the regulation of lactate dehydrogenase and pyruvate formate-lyase.
|
|
| 4. |
- Hofvendahl, Karin, et al.
(författare)
-
Simultaneous enzymatic wheat starch saccharification and fermentation to lactic acid by Lactococcus lactis
- 1999
-
Ingår i: Applied Microbiology and Biotechnology. - : Springer Science and Business Media LLC. - 1432-0614 .- 0175-7598. ; 52:2, s. 163-169
-
Tidskriftsartikel (refereegranskat)abstract
- Simultaneous saccharification of starch from whole-wheat flour and fermentation to lactic acid (SSF) was investigated. For saccharification the commercial enzyme mixture SAN Super 240 L, having alpha-amylase, amyloglucosidase and protease activity, was used, and Lactococcus lactis ssp. lactis ATCC 19435 was used for the fermentation. SSF was studied at flour concentrations corresponding to starch concentrations of 90 g/l and 180 g/l and SAN Super concentrations between 3 mu l/g and 8 mu l/g starch. Kinetic models, developed for the saccharification and fermentation, respectively, were used for simulation and data from SSF experiments were used for model verification. The model simulated SSF when sufficient amounts of nutrients were available during fermentation. This was achieved with high wheat hour concentrations or with addition of yeast extract or amino acids. Nutrient release was dependent on the level of enzyme activity.
|
|
| 5. |
- Lezinou, V., et al.
(författare)
-
Study of a single and mixed culture for the direct bio-conversion of sorghum carbohydrates to ethanol
- 1995
-
Ingår i: Applied Microbiology and Biotechnology. - 0175-7598 .- 1432-0614. ; 43:3, s. 412-415
-
Tidskriftsartikel (refereegranskat)abstract
- Fusaium oxysporum F3 alone or in mixed culture with Saccharomyces cerevisiae 2541 fermented soluble and insoluble carbohydrates of sweet sorghum stalk directly to ethanol. Both microorganisms were first grown aerobically and fermented sorghum stalk to ethanol thereafter. During fermentation, insoluble carbohydrates were hydrolysed to soluble sugars by the celluloytic system of F. oxysporum. Ethanol yields as high as 24.4 and 33.5 g/100 g dry stalks were obtained by F. oxysporum and the mixed culture respectively, representing a theoretical yield enhancement of 11.6% and 53.6% respectively. The corresponding ethanol concentrations in the fermentation medium were 4.6% and 6.4% (w/v). These results clearly demonstrated that a large portion of insoluble carbohydrate from sorghum was converted by simultaneous saccharification and fermentation to ethanol, making the process promising for bioethanol production.
|
|
| 6. |
- Palmqvist, E, et al.
(författare)
-
Evaluation of cell recycling in continuous fermentation of enzymatic hydrolysates of spruce with Saccharomyces cerevisiae and on-line monitoring of glucose and ethanol
- 1998
-
Ingår i: Applied Microbiology and Biotechnology. - : Springer Science and Business Media LLC. - 1432-0614 .- 0175-7598. ; 50:5, s. 545-551
-
Tidskriftsartikel (refereegranskat)abstract
- The maximum growth rate of Saccharomyces cerevisiae ATCC 96581, adapted to fermentation of spent sulphite liquor (SSL), was 7 times higher in SSL of hardwood than the maximum growth rate of bakers' yeast. ATCC 96581 was studied in the continuous fermentation of spruce hydrolysate without and with cell recycling. Ethanol productivity by ATCC 96581 in continuous fermentation of an enzymatic hydrolysate of spruce was increased 4.6 times by employing cell recycling. On-line analysis of CO2, glucose and ethanol (using a microdialysis probe) was used to investigate the effect of fermentation pH on cell growth and ethanol production, and to set the dilution rate. Cell growth in the spruce hydrolysates was strongly influenced by fermentation pH. The fermentation was operated in continuous mode for 210 h and a theoretical ethanol yield on fermentable sugars was obtained.
|
|
| 7. |
- Planas, J, et al.
(författare)
-
Enhanced production of lactic acid through the use of a novel aqueous two-phase system as an extractive fermentation system
- 1996
-
Ingår i: Applied Microbiology and Biotechnology. - : Springer Science and Business Media LLC. - 1432-0614 .- 0175-7598. ; 45:6, s. 737-743
-
Tidskriftsartikel (refereegranskat)abstract
- Abstract (1/2-em) In order to enhance the productivity of lactic acid and reduce the end-product inhibition of fermentation, the partitioning and growth of four different strains of lactic acid bacteria in three different aqueous two-phase systems were studied. Polyethyleneglycol/ dextran, polyethyleneglycol/hydroxypropyl starch polymer (HPS), and a random copolymer of ethylene oxide and propylene oxide (EO-PO)/HPS were used as polymer systems. One strain each of Lactococcus lactis subsp. lactis and of Lactobacillus delbrueckii subsp. delbrueckii partitioned completely to the interface and bottom phase in two-phase systems with low polymer concentrations of EO-PO/HPS100 and EO-PO/ HPS200. The growth and production of lactic acid by two of three L. lactis strains in a two-phase system with 5.5% (w/w) EO-PO and 12.0% (w/w) HPS100 were reduced by less than 10% compared with a reference fermentation in a normal growth medium. The viability of L. lactis subsp. lactis ATCC 19435 was maintained for at least 501/4-em h and with four top-phase replacements during extractive fermentation in the EO-PO/HPS100 system. Moreover, when cell density reached the stationary phase in the first extractive fermentation, the lactate production in this aqueous two-phase system was maintained.
|
|
| 8. |
- Taherzadeh, Mohammad J, 1965-, et al.
(författare)
-
The effects of pantothenate deficiency and acetate addition on anaerobic batch fermentation of glucose by Saccharomyces cerevisiae
- 1996
-
Ingår i: Applied Microbiology and Biotechnology. - : Springer. - 0175-7598 .- 1432-0614. ; 46:2, s. 176-182
-
Tidskriftsartikel (refereegranskat)abstract
- Physiological effects of deficiency of pantothenate, a necessary precursor in the synthesis of coenzyme A, were studied using the yeast strain Saccharomyces cerevisiae CBS 8066. Cells were grown on defined media in anaerobic batch cultures with glucose (50 g/l) as the carbon and energy source. Batch cultures containing more than 60 μg/l pantothenate showed no significant differences with respect to growth rates and product yields. However, with an initial pantothenate concentration of 30 μg/l, the average glucose consumption rate was 50% lower than in rich medium and, at even lower concentrations of pantothenate, the culture did not consume all the glucose in the medium. Furthermore, pantothenate deficiency caused the acetate and pyruvate yields to increase and the biomass yield to decrease, compared to the yields in pantothenate-rich medium. The increased acetate formation could be counteracted by initial addition of acetate to the medium, and thereby the glycerol yield could be decreased. An initial addition of acetate of 1.6 g/l to pantothenate-deficient medium (30 μg/l) caused a 35% decrease in glycerol yield and a 6% increase in ethanol yield. Furthermore, the time required for complete conversion of the glucose decreased by 40%. Acetate addition affected the acetate and glycerol yields in a similar way in pantothenate-rich medium (1000 μg/l) also.
|
|
| 9. |
- van Niel, Ed, et al.
(författare)
-
Nutrient requirements of lactococci in defined growth media
- 1999
-
Ingår i: Applied Microbiology and Biotechnology. - : Springer Science and Business Media LLC. - 1432-0614 .- 0175-7598. ; 52:5, s. 617-627
-
Forskningsöversikt (refereegranskat)abstract
- Many attempts have been made for the last six decades to design defined media for species of the lactococcus group. The general outcome of the studies suggests that this group is heterogeneous with respect to specific requirements for nutrients. Lactococcal species are limited in various metabolic pathways. Early attempts to trace the required nutrients were not always successful because of the poor quality of analysis and the presence of impurities in the medium components.
|
|
| 10. |
- Andersson, Erik, et al.
(författare)
-
Accumulation and degradation of dead-end metabolites during treatment of soil contaminated with polycyclic aromatic hydrocarbons with five strains of white-rot fungi
- 1996
-
Ingår i: Applied Microbiology and Biotechnology. - 1432-0614. ; 46:5-6, s. 647-652
-
Tidskriftsartikel (refereegranskat)abstract
- The white-rot fungi Trametes versicolor PRL 572, Trametes versicolor MUCL 28407, Pleurotus ostreatus MUCL 29527, Pleurotus sajor-caju MUCL 29757 and Phanerochaete chrysosporium DSM 1556 were investigated for their ability to degrade the polycyclic aromatic hydrocarbons (PAH) anthracene, benz[a]anthracene and dibenz[a,h]anthracene in soil. The fungi were grown on wheat straw and mixed with artificially contaminated soil. The results of this study show that, in a heterogeneous soil environment, the fungi have different abilities to degrade PAH, with Trametes showing little or no accumulation of dead-end metabolites and Phanerochaete and Pleurotus showing almost complete conversion of anthracene to 9,10-anthracenedione. In contrast to earlier studies, Phanerochaete showed the ability to degrade the accumulated 9,10-anthracenedione while Pleurotus did not. This proves that, in a heterogeneous soil system, the PAH degradation pattern for white-rot fungi can be quite different from that in a controlled liquid system.
|
|
