Abstract: Faced with an ephemeral prey, aphidophagous ladybirds rely on the hydrocarbons present in the tracks of their larvae to choose an unoccupied patch for egg laying. Although both conspecific and heterospecific larval tracks might deter females from oviposition, the response to the later is often less striking. Several explanations have been suggested to account for this. In this paper we tested the phylogeny hypothesis, which predicts that the chemical composition of the tracks of closely related species of ladybirds will be more similar to one another than to those of more distantly related species. Qualitative and quantitative information on the chemical nature of the larval tracks and a molecular phylogeny of seven species belonging to three different genera are provided, and the congruence between these two sets of results assessed. The results confirm the phylogeny hypothesis and infer a gradual mode of evolution of these infochemicals.
Abstract: The effect of temperatures ranging from 15 to 35 degrees C on a culture of Brettanomyces bruxellensis was investigated in regards to thermodynamics, metabolism, and kinetics. In this temperature range, we observed an increase in growth and production rates. The growth behavior was well represented using the Arrhenius model, and an apparent activation energy of 16.61 kcal/mol was estimated. A stuck fermentation was observed at 35 degrees C as represented by high cell death. The carbon balance established that temperature had no effect on repartition of the glucose consumption between biomass and products. Hence, the same biomass concentration was obtained for all temperatures, except at 35 degrees C. Moreover, using logistic and Luedeking-Piret models, we demonstrated that production rates of ethanol and acetic acid were partially growth associated. Parameters associated with growth (alpha eth and alpha aa) remained constant with changing temperature, whereas, parameters associated with the population (beta eth and beta aa) varied. Optimal values were obtained at 32 degrees C for ethanol and at 25 degrees C for acetic acid.
Abstract: Intraspecific and interspecific predation of eggs is a well documented phenomenon amongst aphidophagous coccinellids. The invasive species Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) is known to be a top intraguild predator and reported to attack the eggs of many coccinellid species both in a laboratory setting and in the wild. A previous laboratory study highlighted that while many species' eggs were highly palatable to H. axyridis, the eggs of Calvia quatuordecimguttata (Linnaeus) (Coleoptera: Coccinellidae) appeared to be extremely well protected from attack. Here we present the results of behavioural experiments testing the hypothesis that substances on the egg surface are responsible for this protection, and report preliminary results of GC-MS analysis of these compounds. When the coatings of C. quatuordecimguttata eggs were removed using hexane, they became significantly more susceptible to predation by neonate H. axyridis larvae. However, their overall palatability was not affected, in that complete consumption was never or rarely observed. This suggests that the surface compounds are a true indicator of unpalatability in this species. The effect of hexane-washing on already palatable conspecific eggs was also analysed but had no significant effect on the susceptibility of eggs to cannibalism. We conclude that the eggs of at least one European species are effectively protected by surface deterrents from intraguild predation by H. axyridis. This effect might be due to both the diversity and abundance of hydrocarbons present within the egg coating, the presence of alkenes and/or the presence of patches of a red substance on the eggs' surface, which is thought to belong to the acid group. In conjunction with data on the susceptibility of other immature stages of C. quatuordecimguttata, this finding may indicate a decreased risk of the species falling victim to invasive H. axyridis, despite their coincident habitat ranges.
Abstract: Kinetics of alcoholic fermentation by Saccharomyces cerevisiae wine strains in a synthetic medium with high sugar content were established for different nitrogen initial content and are presented for four strains. The composition of the medium was close to grape must except that the nitrogen source consisted mainly in ammonium and was varied from 120 to 290 mg N/l assimilable nitrogen. The overall nitrogen consumed was also estimated in order to determine nitrogen requirement variability. The effect of assimilable nitrogen was in general greater on sugar consumption rates than on growth and three kinds of effect on sugar consumption rates were observed: (i) existence of an optimal initial nitrogen level for a maximal sugar consumption rate (inhibition if excess), (ii) no effect of nitrogen beyond the intermediary level (saturation), (iii) sugar consumption rate proportional to the initial nitrogen level (activation). In all cases, the amount of consumed nitrogen increased with its initial concentration and so did the fructophilic capacity of the strains. The optimal requirement varied from 0.62 to 0.91 mg N/g of sugars according to different strains. There was no general correlation between the sugar assimilation rates and the nitrogen requirement.
Abstract: The metabolic pathway shift between only ethanol consumption to both sugar/ethanol consumption was measured by on-line analysis of respiratory quotient of a Saccharomyces cerevisiae. The experiments were carried out in a fed-batch culture under aerobic conditions. During the transition phase, respiratory quotient (RQ) profile shows that sugar can be metabolized through the fermentative pathway even to values of RQ lower than 1.
Abstract: Immobilized cells of Schizosaccharomyces pombe yeast were used for total or partial deacidification of grape must. All experiments were carried out using dry immobilized yeast cells instead of wet immobilized yeast cells as in previous works. Immobilized cells of Schiz. pombe were only used at the beginning of fermentation until partial or total consumption of L-malic acid. Immobilized cells were then removed from the fermentation tank and the must was re-inoculated with a commercial strain of Saccharomyces cerevisiae to achieve alcoholic fermentation. Experiments showed that in terms of kinetics, the high malate fermentation activity of the immobilized yeast cells was similar to that of the non-immobilized cells. Sensorial evaluation showed that the wines obtained using Schiz. pombe had a better organoleptic quality than the wine without deacidification. Analysis of some aromatic compounds (hydrogen sulfide, acetaldehyde, methanol, isopropanol, amyl and iso-amyl alcohols) at the end of the alcoholic fermentation did not show a significant difference in comparison to the control fermentation. Deacidification activity of immobilized yeast cells was maintained for at least 20 months after their encapsulation, at which point they were stored at 4degreesC. Alginate bead quality tests showed that immobilized cells could be recycled up to five times without liberation of yeast cells into wine must.
Abstract: S. pombe has considerable potential in winemaking because of its marked ability to metabolize malic acid of musts, but the yeast must be removed subsequently to prevent the development of off-flavors. S. pombe was immobilized in calcium alginate beads (to facilitate eventual removal of the yeast) and used to eliminate malic acid from both red and white grape musts. The beads were used as a dry product instead of the moistened beads used in previous studies. Expts. on both red and white musts were carried out in the north of Portugal and in the southwest of France under normal winemaking conditions. The immobilized S. pombe consumed ≤0.2 g malic acid/L/h at 20° when an equiv. concn. of 4 million cells/mL was applied. The beads could be re-used 5 times and stored 20 mo without any loss of activity. The wines obtained were characterized by better organoleptic characteristics than control wines. [on SciFinder(R)]
Abstract: In this work, encapsulated whole cells of S. cerevisiae in calcium-alginate gel (S. cerevisiae-CAG) were used for the treatment of sluggish and stuck fermentation in vinification. S. cerevisiae-CAG can be applied into the must grape and then they can be withdrawn easily at the end of alcoholic fermentation. For the treatment of sluggish and stuck fermentations, S. cercvisiae-CAG were applied following two steps: firstly S cerevisiae-CAG were introduced into permeable bags and they were activated in a liquid medium; secondly, after an activation period of eight hours, the immobilized yeast cells were introduced into the fermentation tank. In this work, the obtained results for the treatment of sluggish and stuck fermentations in several French and Portuguese wineries are presented. Preliminary results obtained in micro-vinification conditions have shown that the use of immobilized yeast was better than traditional method (which uses free cells) for the treatment of stuck and sluggish fermentations. The large success rate of immobilized yeast can be explained by one adaptation step of yeast cells to high ethanol concentrations during the immobilization process. The application of immobilized cells of S. cerevisiae under real conditions of vinification has shown a consumption rate of 2.8 g/L per day of reducing sugar with a concentration of 5 million of viable cells per mL. It was never observed any increase of the volatile acidity or of other undesirable compounds.
Abstract: This paper presents a study dealing with the production and consumption kinetics of the main organic acids during alcoholic fermentation carried out by a Saccharomyces cerevisiae strain normally used for winemaking. The experiments were carried out using a synthetic medium in which the initial malic acid concentration and the initial pH value were the parameters studied. The kinetics of malic acid consumption and of some organic acids production was then quantified. The results show that a decrease in pH value favors malic acid consumption, while an increase of the initial malic acid concentration increases the consumed amount. The specific malic acid consumption rate shows that its assimilation was microbial growth independent, while the of her organic acids specific production rates show that their excretion was strongly associated with the microbial growth. The pH evolution during the fermentation was followed and partially explained by the evolution of the global organic acid production.
Abstract: The objective of this work was to better characterize five yeast strains concerning malic acid degrdn., org. acids prodn. and the influence on medium final pH value. Among the five strains, three were considered as yeasts for acidity preservation and two as deacidifying yeasts. In the first step, fermns. were carried out on a synthetic medium in order to best compare the yeast independently of grape must variability. The varying parameters were initial pH and malate concn. Then, the obtained data were compared to 66 expts. of wine making realized by the Institut Technique du Vin. On the synthetic medium the five strains consumed malic acid with different intensity: 25 to 36% for 432 strain, 20 to 32% for AC-, 16 to 32% for FA1m 0 to 16% for 1033 and 0.8 to 4.6% for 1636. The lower was the initial pH value, the higher was the amt. of malate degraded. The effect of the yeast on the final pH was different: whereas three yeasts did not have any influence on it (1033, 1636 and 432), the FA1 strain always diminished it and the AC- strain raised it. This observation must be connected with the org. acids prodn. which could have an influence on medium acidity.
Abstract: This paper presents a kinetic study of the dynamics of the population of two Saccharomyces strains cerevisiae (designated K1 and 522D) in mixed culture. These two strains are commonly used in wine making. The K1 strain (killer yeast) secretes a glycoprotein (killer toxin) which causes the death of the 522D strain (sensitive yeast). Initially, the mixed cultures were realized in batch fermentations. Initial concentrations of killer yeast were 5 and 10% of the total population. The influence of the killer strain on the sensitive cultures was measured in comparison with a reference fermentation. The reference fermentation was inoculated only with the sensitive strain. Results show that an initial concentration of 10% of killer strain affects the microbial population balance and the rate of ethanol production. However the fermentation was only slightly disturbed when the proportion of killer to sensitive yeast at the beginning of mixed culture was 5%. To achieve total displacement by the killer yeast at low concentrations, the mixed cultures were carried out in a continuous system. The results obtained in continuous fermentations with the same strains have shown that a level of contamination as low as 0.8% of killer strain was sufficient to completely displace the original sensitive population after 150 h incubation.
Abstract: This paper presents a kinetic study of two yeasts growing in pure and mixed batch cultures. Two winemaking strains were used: S. cerevisiae K1 possessing the K2 killer character and S. cerevisiae 522D sensitive to the K2 killer toxin. Initially the kinetics of growth of the two strains were analyzed in pure culture. In this case, the kinetic profiles of biomass prodn. have shown that the growth rate of the K1 strain is slightly superior to the 522D strain. During the fermn., the viability for both populations was higher than 90%. Fermns. in mixed culture with an initial percentage in killer strain of 5% and 10% with respect to the total population were carried out. The results showed a more important decrease in the percentage of total viable yeasts when the initial concn. of killer yeast increased. However, the kinetic profiles of total biomass (killer plus sensitive yeasts) were very similar for both fermns. A math. model was proposed to simulate the microbial growth of the killer and sensitive strain developing in pure and mixed cultures. This math. model consists in three main reactions: the evolution of the killer toxin in the culture medium, the duplication and the mortality rates for each microbial population. The results of the simulation appeared in agreement with the exptl. data. [on SciFinder(R)]
Abstract: The Lactobacillus acidophilus growth was investigated to rind the optimal concentrations of 2 nitrogen sources (thought to be in excess) and 2 organic acids. A Plackett and Burman experimental design was used allowing identification of the more important factors with very few experiments. In the studied range, all the factors had a linear effect and a great influence on the final viability. 20 g/L of each nitrogen sources, 3 g sodium-citrate/L and 5 g sodium acetate/L are necessary. pH, temperature and glucose had poor influence.
Abstract: In winemaking, the utilization of selected yeasts has been considerably developed in the last years with the aim of a better control of the alc. fermn. as well as the guarantee of the organoleptic quality of the final products. However, usually the musts of grape for wine prodn. are not sterile and the implantation of a selected yeast strain is not always insured. One of the factors for their implantation is the utilization of yeast strains possessing the "killer" character. Indeed, the genetic expression and biochem. action of killer phenomenon is relatively well known; in contrast, few data about its kinetics during batch fermn. are available. This work presents a study of the growth kinetics of a sensitive strain of Saccharomyces cerevisiae developing in the presence of K2 toxin which has been beforehand produced by a killer S. cerevisiae strain. [on SciFinder(R)]
Abstract: A method, based on the reaction of a sensitive strain being transferred to medium prefermented by a killer strain, is proposed for the quantitative determination of the ''killer'' activity in fermentation media by Saccharomyces cerevisiae K1. This technique enables killer activity to be closely followed throughout the duration of batch fermentation. The killer activity in the culture medium is represented by the percentage decrease inviable biomass in comparison with the viable biomass of a reference culture.
Abstract: A review discussing the immobilization of microbial cells and their applications to the use of yeasts in the food industry. [on SciFinder(R)]
