A comparison of the formation, rheological properties and microstructure of acid skim milk gels made with a bacterial culture or glucono-δ-lactone

Lucey, J.A.; Tamehana, Michelle; Singh, Harjinder; Munro, Peter A.

doi:10.1016/s0963-9969(98)00075-1

Cited by 198 publications

(203 citation statements)

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“…affect the syneresis of fermented milk beverages (LUCEY et al, 1998). The Kefirs fermented with the starter culture were firmer and had lower acidity (Table 2).…”

Section: Firmness and Syneresismentioning

confidence: 99%

“…Fibres, such as inulin, have been reported to reduce syneresis in fermented milks during storage because of their high water holding capacity (APORTELA-PALACIOS; SOSA-MORALES; VÉLEZ-RUIZ, 2005;GUVEN et al, 2005). However, the presence of a long-chain inulin could affect the development of a 3-dimensional structure of casein resulting in a weak gel incapable of retaining water (LUCEY et al, 1998). The results indicate that the influence of inulin on syneresis is related to the type of milk (whole or skim) and starter (grain or culture) used.…”

Section: Firmness and Syneresismentioning

confidence: 99%

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Effect of starter culture and inulin addition on microbial viability, texture, and chemical characteristics of whole or skim milk Kefir

et al. 2012

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The effect of inulin addition and starters (Kefir grains or commercial starter culture) on the microbial viability, texture, and chemical characteristics of Kefir beverages prepared with whole or skim milk was evaluated during refrigerated storage. The type of starter did not influence microbial viability during the storage of the beverages, but the chemical and textural changes (decreases in pH, lactose concentration, and inulin and increased acidity, firmness, and syneresis) were more pronounced in the formulations fermented with grains than those fermented with the starter culture. The addition of inulin did not influence acidity or viability of lactic acid bacteria, but in general, its effect on the survival of acetic acid bacteria, Lactococcus and yeasts, firmness, and syneresis depended on the type of milk and starter culture used. Generally, the yeast, acetic acid bacteria, and Leuconostoc counts increased or remained unchanged, while the total population of lactic acid bacteria and Lactococcus were either reduced by 1 to 2 logs or remained unchanged during storage.

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“…affect the syneresis of fermented milk beverages (LUCEY et al, 1998). The Kefirs fermented with the starter culture were firmer and had lower acidity (Table 2).…”

Section: Firmness and Syneresismentioning

confidence: 99%

Section: Firmness and Syneresismentioning

confidence: 99%

Effect of starter culture and inulin addition on microbial viability, texture, and chemical characteristics of whole or skim milk Kefir

et al. 2012

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“…The aim of the present study is to elucidate the built-up of acid gels made from heated skim milk fermented by lactic acid bacteria. The GDL gel and acid gel obtained by fermentation have different microstructures and rheological properties [27]. This can be due to different acidification rates and diffusion processes.…”

Section: Introductionmentioning

confidence: 99%

“…When the concentration of GDL increases, tan d and the pH at gelation increase [5] and G' slightly decreases [26]. According to Lucey et al [27], a faster gelation, such as that performed at 40°C compared with 20°C, is commonly regarded as conditions leading to coarser networks [27]. Moreover, the effect of temperature on the gel is related to changes in hydrophobic interactions inside the particle and consequently to the ability of the particle inside the network to rearrange in more dense clusters, given lower G' values [26,27].…”

Section: Introductionmentioning

confidence: 99%

“…According to Lucey et al [27], a faster gelation, such as that performed at 40°C compared with 20°C, is commonly regarded as conditions leading to coarser networks [27]. Moreover, the effect of temperature on the gel is related to changes in hydrophobic interactions inside the particle and consequently to the ability of the particle inside the network to rearrange in more dense clusters, given lower G' values [26,27]. Anyway, it must be borne in mind that, according to Ronnegard and Dejmek [36], decreasing the temperature of measurement from 50 to 10°C leads to a high increase in G' and to an increased elasticity of a set yoghurt.…”

Section: Introductionmentioning

confidence: 99%

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Article

Laligant

Famelart

Pâquet

et al. 2003

Lait

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-The behaviour of heat-treated skim milk towards acidification by fermentation with lactic bacteria was studied at 30°C and 42°C. Rheological changes using dynamic oscillations and 1 H-NMR relaxation time, T2, were studied with time and pH. Front-face intrinsic fluorescence measurements studied with principal component analysis were performed during fermentation. The gel was formed at 42°C at a shorter time and a higher pH (5.53 ± 0.01) than at 30°C (5.24 ± 0.13). The maximum in tan d was higher at 42°C than at 30°C, but the G' values at pH 4.6 were the same at the two temperatures. The changes in T2 with pH were not greatly different at the two temperatures, but the dT2/dpH curves showed some differences with the temperature. The changes in T2 were due to the changes in the particle structure caused by the fermentation and were correlated with calcium solubilisation. Front-face fluorescence can detect a first shift of the maximal intensity toward lower wavelengths and a second shift toward longer wavelengths. These shifts were separated by the gel point and were due to changes in the environment of tryptophan residues in the protein chains. The discussion of these results and the comparison with GDL-induced gels take into account the limitation of the transfer of the acid and the protons from the aqueous to the colloidal phase and the subsequent heterogeneity of the gel.Milk / yoghurt / pH / 1 H-NMR / rheology / intrinsic fluorescence Résumé -Fermentation de lait reconstitué et chauffé par des bactéries lactiques à deux températures. II. Approche dynamique de la construction du gel. Le comportement du lait écrémé traité thermiquement au cours de l'acidification par des bactéries lactiques est étudié à 30 et 42°C. Les modifications rhéologiques par oscillations dynamiques et le temps de relaxation T2 en RMN du proton sont étudiés en fonction du temps et du pH. La fluorescence frontale intrinsèque étudiée conjointement avec l'analyse en composantes principales a été suivie au cours de la fermentation. La gélification du lait apparaît à un temps plus court et un pH plus élevé à 42°C (5,53 ± 0,01) qu'à 30°C (5,24 ± 0,13). Le pic de maximum de tan d était plus marqué à 42 qu'à 30°C, mais le G' à pH 4,6 avait la même valeur aux deux températures. Les changements de T2 au cours * Correspondence and reprints E-mail: famelart@rennes.inra.fr 308 A. Laligant et al.de l'acidification étaient peu différents aux deux températures étudiées, mais les courbes dT2/dpH montrent quelques différences entre 42 et 30°C. Les changements de T2 sont dus à des changements de structure de la particule provoqués par la fermentation et sont corrélés à la solubilisation du calcium. La fluorescence frontale détecte un premier décalage des spectres vers des longueurs d'onde plus petites puis un décalage vers des longueurs d'onde plus grandes. Le point associé à l'inversion de l'environnement des tryptophanes des chaînes protéiques correspond au point de gel. Ces résultats et les différences avec des gels acides obtenus par l'addition ...

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Lipid Crystal Characterization

Herrera

Hartel

2001

Current Protocols in Food Analytical Chemistry

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Lipid Crystal Characterization BASIC PROTOCOLThe structure (e.g., number, size, distribution) of fat crystals is difficult to analyze by common microscopy techniques (i.e., electron, polarized light), due to their dense and interconnected microstructure. Images of the internal structures of lipid-based foods can only be obtained by special manipulation of the sample. However, formation of thin sections (polarized light microscopy) or fractured planes (electron microscopy) still typically does not provide adequate resolution of the crystalline phase. Confocal laserscanning microscopy (CLSM), which is based on the detection of fluorescence produced by a dye system when a sample is illuminated with a krypton/argon mixed-gas laser, overcomes these problems. Bulk specimens can be used with CLSM to obtain high-resolution images of lipid crystalline structure in intricate detail.This unit describes the analysis of lipid crystal microstructure using CLSM. A combination of Nile Red and Nile Blue dyes is dissolved in the melted samples. Nile Red is very fluorescent and allows the use of the laser source at ≤10% power, which prevents the dyes from burning or samples from melting. Moreover, crystal structure is well defined and air bubbles are easy to distinguish from crystals. Nile Blue is necessary to better distinguish the background from crystals. This lipophilic stain diffuses into the oil phase of a sample and generates a deep yellow fluorescence, whereas the solid fat does not fluoresce. The combination of dyes described here should be suitable for most fat systems. Sample preparation and image collection are discussed in detail. Familiarity with CLSM techniques is required (see, e.g., Smith, 1998).This protocol is written primarily for samples where the dyes can be added into the molten fat, which can then be observed either in the molten state, if a hot substage is attached to the microscope stage, or after allowing it to solidify. To obtain the best images, dyes should be dissolved in the fats before samples are crystallized. MaterialsNile Red (Sigma) Nile Blue, sulfate salt (Sigma) Fat sample Ovens, 60° and 80°C Razor blade or microtome (optional) Confocal microscope and appropriate fluorescence filter (e.g. Bio-Rad MRC 600 or MRC 1024) Crystallize fat sample 1. Weigh out 0.5 mg Nile Red and 100 mg Nile Blue. It is important to weigh Nile Red accurately. Nile Red modifies lipid nucleation kinetics when used at higher concentrations and, thus, modified crystal images may be obtained if the concentration is too high. The concentration recommended in this protocol has been proven not to modify lipid crystallization kinetics. 2. Melt 500 g fat sample in a beaker and hold at 80°C for 30 min. This procedure will destroy all existing crystals. This temperature and time will be sufficient for most fats. 3. Add dyes to hot sample. Hold sample in an oven at 60°C for ≥5 hr to dissolve dyes. This step is crucial to obtain high-quality images. If enough dye is not dissolved, images will be very poor. Nile Red is very soluble i...

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A comparison of the formation, rheological properties and microstructure of acid skim milk gels made with a bacterial culture or glucono-δ-lactone

Cited by 198 publications

References 19 publications

Effect of starter culture and inulin addition on microbial viability, texture, and chemical characteristics of whole or skim milk Kefir

Effect of starter culture and inulin addition on microbial viability, texture, and chemical characteristics of whole or skim milk Kefir

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Lipid Crystal Characterization

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