The properties of casein micelles in milk concentrates are of interest for the use of ultrafiltered (UF) skim milk concentrates in dairy products, and for the general understanding of colloidal stability and behavior of the casein micelle. The rheological behavior of UF skim milk concentrate with a casein concentration of 19.5% (wt/wt) was investigated at different pH and NaCl concentrations by analyzing flow viscometry and small amplitude oscillatory shear measurements. Viscometric flow curves were fitted to the Carreau-Yasuda model with the aim of determining values for the viscosity at infinite high shear rates and thereby estimate the voluminosity of the casein micelles (nu(casein)) in the UF concentrate. The voluminosity of the casein micelles increased with addition of NaCl and decreased when pH was decreased from 6.5 to 5.5. At pH 5.2, nu(casein) increased because of acid-induced aggregation of the casein micelles. The changes in nu(casein) could be interpreted from transmission electron microscopy of freeze-fractured samples of the UF concentrate and partly from dynamic light scattering measurements. Altered interactions between casein micelles due to different pH and NaCl concentrations are proposed to occur due to collapse of the kappa-casein layer, changed ionic strength, and altered distance between casein micelles.

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Results of this study confirm that high temperature (118 degrees C/15 min) and high pressure (400 MPa/5 min) processing of skim milk, skim milk ultrafiltration and ultracentrifugation fractions, and model milk salt solutions cause dramatic shifts in their colloidal and soluble Ca phosphate equilibrium that affect their pH, dissolved Ca content, turbidity, and casein micelle microstructure. The relations between high temperature and high pressure processing-induced changes in the colloidal and soluble Ca phosphate equilibrium were evaluated in raw, pasteurized, and high temperature treated skim milk, ultrafiltration retentate and permeate of pasteurized skim milk, clear ultracentrifugation infranatant of pasteurized skim milk, and synthetic milk ultrafiltrates with and without lactose or Ca. The magnitude of the pH and dissolved Ca shifts caused by high temperature and high pressure processing was a function of casein micelle concentration. Ultrafiltration permeate exhibited the most drastic shits in pH and dissolved Ca contents due to high temperature and high pressure processing. Although high temperature processing reduced the pH of ultrafiltration permeate from 6.59 to 6.03 and the dissolved Ca from 100% to 58%, high pressure processing reversed both of these changes. These changes in high temperature and high pressure processed milk, milk fractions, and model milk salt solutions were related to microstructural changes in the casein micelles as revealed by electron microscopy.

Both sedation regimens allow nearly identical good controllability of propofol sedation. However, recovery time was significantly slower and hypotension was tended to occur more often in the perfusor group.

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-The present paper describes a comparative study of the gelation properties of whey protein concentrate (WPC) and whey protein isolate (WPI). Penetration measurements as well as rheological studies revealed that the strength of heat-induced gels prepared with WPI was higher than with WPC. In addition, gels with WPI were clearly more elastic than WPC gels. The storage modulus of WPI and the storage and loss moduli of WPC increased with increasing frequency, while the loss modulus of WPI revealed no clear dependence on the frequency, resulting in a greater decrease in the loss angle of WPI with increasing frequency. The superior gelation properties of WPI were mainly due to the higher β-lactoglobulin content as well as to lower fat, lactose and phospholipid contents. However, in this paper it is also discussed whether the low contents of glycomacropeptide, non-protein-nitrogen and proteose peptone in WPI may partly explain the superior gelation properties of these protein products. WPI were more sensible to an increase in the ionic strength (0.1-0.3% NaCl) than WPC, resulting in clearly stronger gels with WPI than with WPC. In the pH ranges of 2-3 and 7-8, elastic and translucent gels could be prepared using WPI, while their gel-forming properties were low between pH 4 and 5. The strongest gels, turbid, but still elastic, were prepared with WPI at pH 6. whey protein concentrate / whey protein isolate / gelation properties Résumé -Présentation d'une étude comparative sur les propriétés de gélification du concentré protéique de lactosérum WPC et de l'isolat protéique de lactosérum WPI. Des mesures de la pénétration ainsi que des études rhéologiques révèlent que la solidité des gels obtenus par gélifi-cation thermique est plus élevée en utilisant WPI que WPC. De plus, les gels avec WPI sont nettement plus élastiques que des gels avec WPC. Le module de stockage de WPI et les modules de stockage et de perte de WPC augmentaient avec une fréquence croissante, tandis que les modules de perte de WPI n'étaient pas influencés par la fréquence, et menaient ainsi à une forte réduction de l'angle de perte de WPI avec une fréquence croissante. Les propriétés supérieures de gélification de WPI sont principalement dues à une teneur élevée en β-lactoglobuline et à une teneur réduite en matière grasse, lactose et phospholipide. Dans l'étude présente, il est également discuté si les faibles teneurs en glycomacropeptide, en azote non-protéique de WPI et en protéose peptone dans WPI expliquent partiellement les propriétés supérieures de gélification de ces produits protéiques. WPI réagissait plus sensiblement à une augmentation de la teneur ionique (0.1-0.3% NaCl) que WPC, aboutissant à des gels ostensiblement plus solides avec WPI qu'avec WPC. Avec un pH entre 2-3 et 7-8, il a été possible de préparer des gels élastiques et translucides en utilisant WPI, tandis que les propriétés gélifiantes étaient faibles avec un pH entre 4-5. Les gels les plus solides, d'un aspect trouble mais encore élastiques, étaient préparés avec WPI à...

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Summary To apply native casein micelles (CM) as nanocarriers for lipophilic substances in non‐ or low‐fat food products, they have to be conditioned before loading. In this study, an experimental set‐up for the production and loading of CM was developed. Microfiltration was used to separate CM from skimmed milk. To identify optimal loading conditions temperatures (2, 20, 40 °C), pH values (6.8 and 5.5) and holding times (5, 15, 30, 60 min) were varied. The release of calcium, phosphate and protein from the micellar phase as well as static light scattering and transmission electron microscopy showed that CM were optimally primed at 2 °C and a pH of 5.5 for 5 min. Therefore, loading with β‐carotene was performed under those conditions. After the back‐extraction of β‐carotene, the photometrical analyses revealed total recovery rates of >79% whereby 94% of it was associated with the native CM.