Authors:K. Dénes, Cs. Farkas, Á. Hoschke, J. Rezessy-Szabó, and Q. Nguyen
Effects of mixed cultures of Saccharomyces cerevisiae Levuline FB — higher ethanol tolerance — and different Kluyveromyces strains — higher inulinase activity — on the production of ethanol from Jerusalem artichoke extract were investigated. Among the investigated strains, combination of S. cerevisiae and K. marxianus strain Y00959 with simultaneous saccharification and fermentation gave the best efficiency (76%) of bioconversion. The optimal ratio of mixed cultures was determined to be 1:1 of K. marxianus and S. cerevisiae. Central composite design (CCD) was adapted to find the optimum initial substrate concentration and inoculum size for the maximal production of ethanol from Jerusalem artichoke juice. The optimum fermentation conditions were found to be 24% (m/w) substrate concentration and 45 OD600nm ml/100 ml inoculum size of mixed culture. Use of these conditions, about 10.67% (v/v) was produced at 148 h of alcoholic fermentation given. Results of this work provide benefits of mixed culture on production of bioethanol from Jerusalem artichoke.
Competition between a bacteriocinogenic and a non-bacteriocinogenic Lactococcus lactis strain, respectively, and a Listeria monocytogenes strain was studied in two semi-synthetic liquid media at various temperatures. The media used for the study were ST I and modified ST I broth (ST I broth + 1 g l-1 Tween 80). In both media, at 30 °C, a significant cell count reduction (5 log) of L. monocytogenes occurred only when the cell concentration of the bacteriocinogenic competitor reached the level of at least 107 CFU ml-1 required for the production of sufficient concentration of nisin-like bacteriocin. The same phenomenon was also observed when the initial level of the lactic acid bacteria (LAB) was one log higher or lower than that of the Listeria, however, the reduction of Listeria cell count occurred earlier with the higher initial concentration of the LAB. Incubation of the mixed cultures at 20 °C gave similar results but the bacteriocinogenic activity resulted in only a three log decline of the cell count of L. monocytogenes. At 10 °C Lactococcus lactis produced much less bacteriocin than at 30 °C, therefore, a drastic decrease of the Listeria cell count was not observed. Suppression of the Listeria growth was expressed in its decreased maximum population level (i.e. in an earlier appearance of the stationary phase). When the non-bacteriocinogenic Lac. lactis and Listeria were present at the same initial level (approx. 105 CFU ml-1), the Lactococcus did not affect the growth of L. monocytogenes at 30 °C in modified ST I broth.
Schiemann, D. A. & Olson, S. (1984): Antagonism by Gram-negative bacteria to growth of Yersinia enterocolitica in mixedcultures. Appl. environ. Microbiol. , 48 , 539-544.
Antagonism by Gram-negative bacteria to growth of
The supply and consumption of probiotic foods, and particularly probiotic dairy products, has grown steadily in recent years.
In the production of dairy products of this type other microbes must also be used in addition to the microbes which provide
the probiotic effect and which generally have a proliferation optimum at 37C. The probiotic microbes have a neutral taste
in dairy products consequently the taste of fermented dairy products is supplied by other microbes. These microbes are likewise
lactic acid bacteria, and their proliferation optima are either below (mesophilic) or above (thermophilic) that of the probiotic
microbes. It is imperative to have an indication of whether the probiotic bacteria have multiplied at the fermentation temperature
used during the technology, since they provide the beneficial physiological effect of the product. Isothermic calorimetry
appeared a suitable method for the indication of this process, because the amount of heat released during lactic acid bacterial
proliferation differs from the probiotic one. In order to analyze the heat flow curves a deconvolutional program was developed
which decomposed them into Gaussian curves, because the proliferation of individual microbes follows a lognormal distribution.
The Gaussian curve characteristic for the culture was determined, and from the area under the curve the heat liberated during
the creation of one microbe was calculated.
potentiality of building renovation, whether the function of entertainment, urban agriculture and commerce could combine. 3.2 What can be indicated through the studies above Brigittaplatz is a residential community with a mixedculture, diverse function of
Conductimetry as an alternative data capture method for following microbial growth has a great potential as a research tool of predictive microbiology. In spite of this fact there is only a limited number of applications using conductimetric data for model generation. In this study the growth of single strains of Listeria monocytogenes and Lactococcus lactis was tested in 5 media using a RABITinstrument. The goal of the work was to find selective growth media for Listeria and Lactococcus, respectively, in order to study their interaction in mixed-culture using the conductimetric technique. Whitley Anaerobic broth, Whitley Impedance broth and modified Whitely Impedance broth (Whitley Impedance broth + Chloramphenicol 7 mg l &1) were not suitable for following selectively the growth of Lactococcus lactis or Listeria monocytogenes in a mixed culture of the two bacteria. BiMedia 630 A for Lactococcus lactis and Bimedia 403 A for Listeria monocytogenes satisfied the demands raised by conductance measurement. Linear correlations were established between the graphically estimated TTD values of the conductance curves and the logarithmic numbers of colony forming units (CFU). The correlations were very strong in each case (determination coefficients (R 2) of the linear regression were higher than 0.98 at both medium-strain combinations). However, in BiMedia 630 Listeria monocytogenes was capable of slow growth, therefore, this medium would be feasible for studying microbial interactions if only low concentrations of Listeria (less than 10 6 CFU ml &1) were present in the mixed culture.