Personne :
St-Gelais, Daniel

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Université Laval. Département des sciences des aliments
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Voici les éléments 1 - 7 sur 7
  • Publication
    Accès libre
    Characterization of syneresis phenomena in stirred acid milk gel using low frequency nuclear magnetic resonance on hydrogen and image analyses
    (Oxford : IRL Press, 2020-04-15) Gilbert, Audrey; Rioux, Laurie-Eve; St-Gelais, Daniel; Turgeon, Sylvie
    Water retention is an important quality attribute for yogurt. Classically, stirred yogurt water retention is investigated using induced syneresis measurement (centrifugation), which does not characterize spontaneous syneresis. Low-frequency nuclear magnetic resonance (1H-LF-NMR) is a non-destructive technique to detect spontaneous syneresis. Experimental yogurt from pasteurized skim milk, and commercial stirred yogurts were analyzed with 1H-LF-NMR. After Laplace's transformation of the signal, hydrogen atoms pools were differentiated according to their mobility. Each hydrogen pool stood for a type of water mobility in the matrices characterized by a relaxation time (T2(i)), and a signal intensity (I2(i)). Yogurt water retention was assessed by induced syneresis and their structure was characterized using microscopy. Low frequency 1H-NMR detected four different water mobility groups in the matrices. Among these, there was a signal from bulk water, and another attributed to the separated serum (spontaneous syneresis). In experimental yogurts, spontaneous syneresis was visible, resulting in induced syneresis higher than 50%. Moreover, induced syneresis and spontaneous syneresis detected by 1H-LF-NMR were similar. In commercial yogurts, bulk water mobility reduced with increasing protein content and protein network density. Induced syneresis and bulk-water mobility correlated only in yogurts without gelatin. In the presence of gelatin, the network was more open, probably favoring bulk water mobility. This study shows that 1H-LF-NMR associated with microscopy image analysis efficiently assesses and describes yogurts water retention and spontaneous syneresis.
  • Publication
    Accès libre
    Metatranscriptome analysis of fungal strains Penicillium and Geotrichum reveal cheese matrix breakdown and potential development of sensory properties of ripened Camembert-type cheese
    (MEDLINE/PubMed (U.S. National Library of Medicine), 2014-03-26) Viel, Catherine; Lessard, Marie-Hélène; Boyle, Brian; Labrie, Steve; St-Gelais, Daniel
    Camembert-type cheese ripening is driven mainly by fungal microflora including Geotrichum candidum and Penicillium camemberti. These species are major contributors to the texture and flavour of typical bloomy rind cheeses. Biochemical studies showed that G. candidum reduces bitterness, enhances sulphur flavors through amino acid catabolism and has an impact on rind texture, firmness and thickness, while P. camemberti is responsible for the white and bloomy aspect of the rind, and produces enzymes involved in proteolysis and lipolysis activities. However, very little is known about the genetic determinants that code for these activities and their expression profile over time during the ripening process.
  • Publication
    Accès libre
    The composition of Camembert cheese-ripening cultures modulates both mycelial growth and appearance
    (American Society of Microbiology, 2012-01-13) Lessard, Marie-Hélène; Bélanger, Gaétan; Labrie, Steve; St-Gelais, Daniel
    The fungal microbiota of bloomy-rind cheeses, such as Camembert, forms a complex ecosystem that has not been well studied, and its monitoring during the ripening period remains a challenge. One limitation of enumerating yeasts and molds on traditional agar media is that hyphae are multicellular structures, and colonies on a petri dish rarely develop from single cells. In addition, fungi tend to rapidly invade agar surfaces, covering small yeast colonies and resulting in an underestimation of their number. In this study, we developed a real-time quantitative PCR (qPCR) method using TaqMan probes to quantify a mixed fungal community containing the most common dairy yeasts and molds: Penicillium camemberti, Geotrichum candidum, Debaryomyces hansenii, and Kluyveromyces lactis on soft-cheese model curds (SCMC). The qPCR method was optimized and validated on pure cultures and used to evaluate the growth dynamics of a ripening culture containing P. camemberti, G. candidum, and K. lactis on the surface of the SCMC during a 31-day ripening period. The results showed that P. camemberti and G. candidum quickly dominated the ecosystem, while K. lactis remained less abundant. When added to this ecosystem, D. hansenii completely inhibited the growth of K. lactis in addition to reducing the growth of the other fungi. This result was confirmed by the decrease in the mycelium biomass on SCMC. This study compares culture-dependent and qPCR methods to successfully quantify complex fungal microbiota on a model curd simulating Camembert-type cheese.
  • Publication
    Fat-free yogurt made using a galactose-positive exopolysaccharide-producing recombinant strain of Streptococcus thermophilus
    (American Dairy Science Association, 2010-01-08) Vadeboncoeur, Christian; Moineau, Sylvain; Robitaille, Gilles; Britten, Michel; Tremblay, André; St-Gelais, Daniel
    To prevent textural defects in low-fat and fat-free yogurts, fat substitutes are routinely added to milk. In situ production of exopolysaccharides (EPS) by starter cultures is an acknowledged alternative to the addition of biothickeners. With the aim of increasing in situ EPS production, a recombinant galactose-positive EPS+ Streptococcus thermophilus strain, RD-534-S1, was generated and compared with the parent galactosenegative EPS+ strain RD-534. The RD-534-S1 strain produced up to 84 mg/L of EPS during a single-strain milk fermentation process, which represented 1.3 times more than the EPS produced by strain RD-534. Under conditions that mimic industrial yogurt production, the starter culture consisting of RD-534-S1 and (EPS−) Lactobacillus bulgaricus L210R strain (RD-534-S1/ L210R) led to an EPS production increase of 1.65- fold as compared with RD-534-S1 alone. However, the amount of EPS produced did not differ from that found in yogurts produced using an isogenic starter culture that included the parent S. thermophilus strain RD-534 and Lb. bulgaricus L210R (RD-534/L210R). Moreover, the gel characteristics of set-style yogurt and the rheological properties of stirred-style yogurt produced using RD-534-S1/L210R were similar to the values obtained for yogurts made with RD-534/L210R. In conclusion, it is possible to increase the production of EPS by ropy S. thermophilus strains through genetic engineering of galactose metabolism. However, when used in combination with Lb. bulgaricus for yogurt manufacture, the EPS overproduction of recombinant strain is not significant.
  • Publication
    Accès libre
    Improving the safety of Staphylococcus aureus polyvalent phages by their production on a Staphylococcus xylosus strain
    (Public Library of Science, 2014-07-25) Dumaresq, Jeannot; Labrie, Steve; Moineau, Sylvain; Plante, Pier-Luc; Katsarava, Ramaz; El Haddad, Lynn; St-Gelais, Daniel; Ben Abdallah, Nour
    Team1 (vB_SauM_Team1) is a polyvalent staphylococcal phage belonging to the Myoviridae family. Phage Team1 was propagated on a Staphylococcus aureus strain and a non-pathogenic Staphylococcus xylosus strain used in industrial meat fermentation. The two Team1 preparations were compared with respect to their microbiological and genomic properties. The burst sizes, latent periods, and host ranges of the two derivatives were identical as were their genome sequences. Phage Team1 has 140,903 bp of double stranded DNA encoding for 217 open reading frames and 4 tRNAs. Comparative genomic analysis revealed similarities to staphylococcal phages ISP (97%) and G1 (97%). The host range of Team1 was compared to the well-known polyvalent staphylococcal phages phi812 and K using a panel of 57 S. aureus strains collected from various sources. These bacterial strains were found to represent 18 sequence types (MLST) and 14 clonal complexes (eBURST). Altogether, the three phages propagated on S. xylosus lysed 52 out of 57 distinct strains of S. aureus. The identification of phage-insensitive strains underlines the importance of designing phage cocktails with broadly varying and overlapping host ranges. Taken altogether, our study suggests that some staphylococcal phages can be propagated on food-grade bacteria for biocontrol and safety purposes.
  • Publication
    Efficacy of two Staphylococcus aureus phage cocktails in cheese production
    (Elsevier Science Publishers, 2015-10-05) Labrie, Steve; Roy, Jean-Pierre; Moineau, Sylvain; Khalil, Georges E.; Champagne, Claude P.; El Haddad, Lynn; St-Gelais, Daniel
    Staphylococcus aureus is one of the most prevalent pathogenic bacteria contaminating dairy products. In an effort to reduce food safety risks, virulent phages are investigated as antibacterial agents to control foodborne pathogens. The aim of this study was to compare sets of virulent phages, design phage cocktails, and use them in a cocktail to control pathogenic staphylococci in cheese. Six selected phages belonging to the three Caudovirales families (Myoviridae, Siphoviridae, Podoviridae) were strictly lytic, had a broad host range, and did not carry genes coding for virulence traits in their genomes. However, they were sensitive to pasteurization. At MOI levels of 15, 45, and 150, two anti-S. aureus phage cocktails, each containing three phages, one from each of the three phage families, eradicated a 106 CFU/g S. aureus population after 14 days of Cheddar cheese curd ripening at 4 °C. The use of these phages did not trigger over-production of S. aureus enterotoxin C. The use of phage cocktails and their rotation may prevent the emergence of phage resistant bacterial strains.
  • Publication
    Detection and quantification of capsular exopolysaccharides from Streptococcus thermophilus using lectin probes
    (American Dairy Science Association, 2010-02-26) Vadeboncoeur, Christian; Moineau, Sylvain; Robitaille, Gilles; Britten, Michel; St-Gelais, Daniel
    The aim of this work was to use fluorescently labeled lectins to develop a convenient and reliable method to determine the relative abundance of capsular polysaccharides (CPS) at the surface of Streptococcus thermophilus MR-1C cells. Fluorescein isothiocyanate–labeled peanut agglutinin isolated from Arachis hypogaea was found to interact specifically with the CPS of Strep. thermophilus MR-1C. This labeled lectin was then used as an effective probe to detect and quantify CPS. A fluorescence-based lectin-binding assay was successfully applied to follow the accumulation of CPS during the growth of Strep. thermophilus MR-1C in milk and in M17 broth supplemented with lactose. Our results showed that in both media, CPS production by Strep. thermophilus MR-1C began during the exponential phase of growth and continued for several hours after the culture reached the stationary growth phase.