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 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 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.