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Lactobacillus casei group: identification, characterization and genetic evaluation of the stress response
Full text linkLactic acid bacteria (LAB) are an heterogeneous group of microorganisms used as starter and/or adjunctive cultures in the production of fermented foods to improve the shelf-life, the organoleptic properties and promote health. Many of these species, in fact, have been extensively characterized as probiotics several studies and clinical tests to substantiate health claims are available for several of them. During use, formulation and preservation as starter, adjunctive and/or probiotic cultures LAB are subjected to physical and chemical stresses that can influence growth, cell viability and fermentation capabilities, changing the technological fitness of the strains.
This thesis focused on Lactobacillus casei, L. rhamnosus and L. paracasei with the aim to encrease the knowledge on this strains. These microbial species are involved in the fermentation of various food matrices (meat, vegetable and dairy products) and they could be used as probiotics or for the development of new functional products, as many studies reported the presence of several strains belonging to these species with probiotic features.
Considering the hardness existing in the correct identification of these strains, so genetically close to each other, a wide collection of strains isolated from several sources and previously identified as belonging to L. casei group was collected (201 total strains), and a species-specific PCR, multiplex PCR, group-specific PCR and HRM analyses have been performed or developed to identify L. casei, L. rhamnosus and L. paracasei strains. Almost all the techniques resulted effective for the identification, but the group-specific PCR had to be applied as the first step of identification. Anyway, the attribution to one of the species of the group remained uncertain for some strains.
Therefore, all the strains were characterized using three different assays (Rep-PCR, RAPD-PCR and Sau-PCR), in order to have a complete point of view of their genotype. As a result, a high variability was found among strains with all the three performed assays, confirming the presence of a high number of genotipes.
Therafter 45 strains were selected for the development of an MLST scheme based on the analysis of internal fragments (loci) of stress related genes. The results confirmed the presence of a high variability among strains and it was not surprising to found strains with different STs. Considering that the analysis was performed on 45 strains, and the high number of STs that has been found, it would be interesting to charachterize other strains, in order to find possible correlation between the source of isolation or a specific stress response behaviour. Four-teen strains were selected for the whole genome sequencing and core-genome and pan-genome comparisons were performed, obtaining a clear distinction among L. paracasei and L. rhamnosus strains. Nonetheless, a L. paracasei and two L. casei strains grouped in L. rhamnosus cluster, confirming how hard is the discrimination among these species, because of their high level of similarity.
SAPD-PCR analysis were also performed, confirming a high genomic variability among strains.
The same strains where then subjected to the evaluation of their mucus binding capabilities. The binding assays were performed in vitro and the strains were tested before and after oxidative stress exposure. The behaviour of the microorganisms analysed resulted strain-dependent and analysis allowed the selection of few strains with interesting binding properties, that will be further analysed for their probiotic characteristics before to do in vivo analysis and to understand their adhesion mechanisms.
At least, a strain of L. paracasei was selected for its ability to conduct malolactic fermentation under different EtOH and pH conditions studing how the expression of stress related genes was affected in the different tested conditions. The strain resulted able to performe MLF under all the tested conditions, and as expected, the lower concentration of glucose, corresponding to the lower final concentration of alcohol, demonstrated to be less stressful. Considering that the strain was able to conduct MLF also when in the presence of a concentration of glucose, corresponding to 15% v/v of ethanol, it can be considered as a potential good MLF starter culture. Another topic for the future research could be the evaluation of the stress response of this strain during MLF when adapted in a respiratory envinronment before the inoculatio
Effects of anaerobic and respiratory adaptation on the physiological response of Lactobacillus casei N87
No full textPotential of High Pressure Homogenization for the production of yeast autolysates for winemaking
No full textYeast derivatives (YDs – e.g. inactive dry yeasts and yeast autolysates) are extensively used in winemaking for a wide series of applications: fermentation enhancers, flavor and aroma modulators, scavengers against undesired compounds and antioxidant preparations. Their ability in releasing soluble compounds and macromolecules suggests their potential application to simulate the traditional practice of ageing on the lees. Nevertheless, one of the problems connected with the use of such additives during wine ageing is that they may be responsible of the release off-odors into the wine. These compounds are mostly originated from the development of Maillard reaction or lipid oxidation, during the thermal treatments applied for YDs manufacturing. Thus, the development of non-thermal alternative processes for the obtainment of such products may open new opportunities for the production of commercial preparations, specifically tailored for winemaking use. High pressure homogenization (HPH) is a mechanical processing method, used since 1970s to promote the extraction of intracellular components from microorganisms, including Saccharomyces spp. The ability of HPH to induce cell breakdown is connected with different phenomena (i.e. turbulence, cavitation and shear), occurring when a yeast suspension is forced through the homogenization valve. In the present study, HPH was tested in different conditions (pressure, number of passes) and temperature regimes (controlled vs. uncontrolled), concerning its potential application for the production of yeast autolysates. The performances of this technology were assessed on a commercial strain of Saccharomyces bayanus for winemaking. The autolysates obtained were characterized for their ability to release soluble molecules (e.g. proteins and free amino acids) and glucidic colloids (e.g. glycoproteins) in wine-like medium, for the number of viable cells after the treatment, as well as for their composition regarding volatile compounds, in comparison with both thermolysis and a commercially available YD preparation. HPH demonstrated its capacity in promoting yeast autolysis in a short time and without intensive heating. The release of glucidic colloids increased by increasing the pressure applied and the number of passes and was comparable, or slightly higher, respect to the amounts detected in both thermolysates and the commercial YD preparation. HPH processing variables affected the volatile composition of the final products and their content in amino acids and colloids: in particular, the choice to control or not the processing temperature may allow to obtain autolysates with different characteristics, and suitable for different winemaking applications (i.e. fermentation enhancers or ageing supplements). Compared to thermal treatment, HPH was less effective in promoting Saccharomyces bayanus inactivation. The autolysates produced by HPH showed a more interesting volatile composition, with respect to those obtained by thermolysis, because of the higher content of ethyl esters
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Application of multi-pass high pressure homogenization under variable temperature regimes to induce autolysis of wine yeasts
Full text linkThe effects of the number of passes and processing temperature management (controlled vs. uncontrolled)
were investigated during high pressure homogenization-induced autolysis of Saccharomyces
bayanus wine yeasts, treated at 150 MPa. Both variables were able to affect cell viability, and the release
of soluble molecules (free amino acids, proteins and glucidic colloids), but the effect of temperature was
more important. S. bayanus cells were completely inactivated in 10 passes without temperature control
(corresponding to a processing temperature of 75 C). The two processing variables also affected the volatile
composition of the autolysates produced: higher temperatures led to a lower concentration of volatile
compounds. The management of the operating conditions may allow the compositional characteristics of
the products to be modulated, making them suitable for different winemaking applications
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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