Personne : Turgeon, Sylvie
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Université Laval. Département des sciences des aliments
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- PublicationAccès libreCharacterization 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, SylvieWater 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.
- PublicationAccès libreQuantitative PCR reveals the frequency and distribution of 3 indigenous yeast species across a range of specialty cheeses(American Dairy Science Association, 2022-09-14) Lamarche, Andréanne; Lessard, Marie-Hélène; Viel, Catherine; Turgeon, Sylvie; St-Gelais, Daniel; Labrie, SteveIndigenous microorganisms are important components of the complex ecosystem of many dairy foods including cheeses, and they are potential contributors to the development of a specific cheese's sensory properties. Among these indigenous microorganisms are the yeasts Cyberlindnera jadinii, Pichia kudriavzevii, and Kazachstania servazzii, which were previously detected using traditional microbiological methods in both raw milk and some artisanal specialty cheeses produced in the province of Québec, Canada. However, their levels across different cheese varieties are unknown. A highly specific and sensitive real-time quantitative PCR assay was developed to quantitate these yeast species in a variety of specialty cheeses (bloomy-rind, washed-rind, and natural-rind cheeses from raw, thermized, and pasteurized milks). The specificity of the quantitative PCR assay was validated, and it showed no cross-amplification with 11 other fungal microorganisms usually found in bloomy-rind and washed-rind cheeses. Cyberlindnera jadinii and P. kudriavzevii were found in the majority of the cheeses analyzed (25 of 29 and 24 of 29 cheeses, respectively) in concentrations up to 104 to 108 gene copies/g in the cheese cores, which are considered oxygen-poor environments, and 101 to 104 gene copies/cm2 in the rind. However, their high abundance was not observed in the same samples. Whereas C. jadinii was present and dominant in all core and rind samples, P. kudriavzevii was mostly present in cheese cores. In contrast, K. servazzii was present in the rinds of only 2 cheeses, in concentrations ranging from 101 to 103 gene copies/cm2, and in 1 cheese core at 105 gene copies/g. Thus, in the ecosystems of specialty cheeses, indigenous yeasts are highly frequent but variable, with certain species selectively present in specific varieties. These results shed light on some indigenous yeasts that establish during the ripening of specialty cheeses.
- PublicationAccès libreHow do smoothing conditions and storage time change syneresis, rheological and microstructural properties of nonfat stirred acid milk gel?(Barking, Essex, England : Elsevier Applied Science, 2020-07-16) Guénard Lampron, Valérie; Bosc, Véronique; St-Gelais, Daniel; Villeneuve, Sébastien; Turgeon, SylvieNonfat acid milk gel, acidified by GDL, was used to simulate microbial fermentation of milk to produce stirred yoghurt. Acid milk gel preparation at laboratory scale included stirring, pumping, smoothing and cooling operations. Two filters (pre-smoothed, 1 mm; smoothed, 500 μm), three smoothing temperatures (13, 22 and 35 °C) and two storage times (1 and 22 days) were studied. Syneresis, microgels size and smoothness of microgels were analysed for pre-smoothed and smoothed gels; viscosity, storage modulus, firmness and total pore area were only analysed for smoothed gel. After 1 and 22 days of storage, pre-smoothed gels developed lower syneresis and smaller microgels than smoothed gels at 22 °C. For smoothed gels, regardless of the smoothing temperature, syneresis, firmness, microgels size and smoothness increased during storage, while total pore area decreased and viscosity remained stable. Viscosity was lower when smoothing was performed at 35 °C and was correlated to rougher microgels.
- PublicationAccès libreImpact of starch and exopolysaccharide-producing lactic acid bacteria on the properties of set and stirred yoghurts(New York (N.Y.) : Elsevier, 2016-01-21) Gentès, Marie-Claude; Turgeon, Sylvie; St-Gelais, DanielThe impact of exopolysaccharide (EPS)-producing lactic acid bacteria with well-known structures and starch (0.75%) on the rheological properties (apparent viscosity and elastic modulus) and physical properties (syneresis) of set and stirred yoghurts was studied. Three EPS-producing strains with different structural characteristics were studied: Streptococcus thermophilus ST1 (anionic, stiff and linear EPS), Lactobacillus delbrueckii subsp. bulgaricus LB1 (neutral, stiff and ramified EPS) and Lb. delbrueckii subsp. bulgaricus LB2 (neutral, flexible and highly ramified EPS). The presence of linear, stiff, and anionic EPS from ST1 increased the elastic modulus in all yoghurt conditions, possibly owing to electrostatic interactions with caseins. Higher viscosity values were obtained with stiff and linear or slightly branched EPS from the ST1 and LB1 for all yoghurt conditions. Starch addition increased the values of the rheological and physical properties of all stirred yoghurts, probably due to the repulsion between proteins and polysaccharides favouring thermodynamic incompatibility.
- PublicationAccès libreRelationship between smoothing temperature, storage time, syneresis and rheological properties of stirred yogurt(Barking, Essex, England : Elsevier Applied Science, 2020-05-23) Guénard Lampron, Valérie; Villeneuve, Sébastien; St-Gelais, Daniel; Turgeon, SylvieSix different smoothing temperatures were compared for nonfat yogurt and the changes in syneresis and rheological properties observed for up to 22 days. Multiple linear regressions were used to describe the syneresis, firmness, flow time, viscosity, and flow resistance and the relationship between these properties, the smoothing temperature and the storage time. During storage, viscosity, firmness, and flow time increased; syneresis and flow resistance remained stable. Syneresis increased significantly (P ≤ 0.05) with smoothing temperature (10–35 °C). Other properties increased slightly (P > 0.05), and properties started to decrease above 30 °C. Syneresis, viscosity, and flow resistance were more sensitive to smoothing temperature; firmness and flow time were more sensitive to storage time. Lower smoothing temperature (10 °C) should be used to minimize syneresis while smoothing temperature ranging from 25 to 30 °C is better to improve rheological properties. Storage time must be considered to optimize these properties.