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Query: UMLS:C0851184 (thinning)
 11,252 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In milk, casein occurs as colloidal particles with an average size of about 100 nm. These are stabilized against flocculation by an outer layer of several thousands of kappa-casein molecules. Stability of micelles is characterized by the magnitude of the Smoluchowskian flocculation rate constant, which during the renneting of milk nearly approaches the diffusion-controlled limit. The processes of the clotting of milk by rennet and the phenomena of age-thinning and age-thickening of ultra-high temperature-sterilized, concentrated milks bear interesting kinetic resemblances. Both processes are characterized by a lag phase during which viscosity decreases, followed by an explosive increase in viscosity. In the milk-clotting process, the decrease can be explained by the proteolytic action of the renneting enzyme. This strongly suggests that age-thinning and age-thickening are also caused by the action of a protease that survived the sterilization process. A quantitative check of this theory is difficult because of the apparently small amount of enzyme.
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PMID:Stable and unstable casein micelles. 681 43

Low dietary intake is common in elderly males with low femoral neck areal bone mineral density (BMD). To evaluate the selective influence of a low-protein diet in the pathogenesis of osteoporosis in males and to uncover early and late adaptation of bone cells to protein deficiency, 8-month-old male rats were pair-fed a control (15% casein) or isocaloric low-protein (2.5% casein) diet for 1 or 7 months. BMD, bone ultimate strength, stiffness, and absorbed energy were measured in tibia proximal metaphysis and diaphysis. After double-labeling, histomorphometric analysis was performed at the same sites. Serum osteocalcin, insulin-like growth factor I (IGF-I), and urinary deoxypyridinoline excretion were measured. In proximal tibia, isocaloric low-protein diet significantly decreases BMD (12%), cancellous bone mass (71%), and trabecular thickness (Tb.Th; 30%), resulting in a significant reduction in ultimate strength (27%). In cortical middiaphysis, a low-protein diet decreases BMD (9%) and enlarges the medullary cavity (36%), leading to cortical thinning and lower mechanical strength (20%). In cancellous bone, protein deficiency transiently depresses the bone formation rate (BFR; 60%), osteoid seam thickness (15%), and mineral apposition rate (MAR; 20%), indicating a decrease in osteoblast recruitment and activity. Cortical loss (15%) results from an imbalance between endosteal modeling drifts with impaired BFR (70%). From the first week of protein deficiency, osteocalcin and IGF-I levels drop significantly. Bone resorption activity and urinary deoxypyridinoline remain unchanged throughout the experiment. Protein deficiency in aged male rats induces cortical and trabecular thinning, and decreases bone strength, in association with a remodeling imbalance with a bone formation impairment and a decrease in IGF-I levels.
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PMID:Dietary protein deficiency induces osteoporosis in aged male rats. 1093 54

Physico-chemical properties of retentates obtained from selective concentration of skim milk up to 8 times its original weight using a microfiltration system were studied. The effects of process variables, namely concentration (8.6 to 27 wt.%), temperature (20 to 50 degrees C) and pH (6.0, 6.3, and 6.5) on density (rho), apparent viscosity (mu(a)), consistency coefficient (K), flow behavior index (n), and activation energy (Ea) of the retentates were examined. Depending on pH, retentates showed significant increase in apparent viscosity, deviated from classical Newtonian behavior and exhibited shear-thinning between 11 to 17% solids concentration. No yield stress was detected in the range of concentration studied. The power law parameters (n and K) followed a similar trend. An Arrhenius-type equation described well the effect of temperature on apparent viscosity. Although activation energy increased 120 to 130% for a threefold increase in solids concentration, it was not significantly different from that of other types of concentrated milk at approximately the same concentration. Increasing solids were responsible for change in flow properties with concentration, while the effect of pH was attributed to differential protein (primarily casein) retention and the change in solvation properties and voluminosity of casein micelles. Models relating concentration, temperature, and pH to retentate apparent viscosity and consistency coefficient were identified. Skim milk microfiltration with in-process pH adjustment produces retentates depleted in whey proteins and calcium with significantly altered properties.
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PMID:Physico-chemical properties of skim milk retentates from microfiltration. 1176 78

Tyrosinase was used to initiate the grafting of peptides onto the amine-containing polysaccharide chitosan. Chemical evidence for covalent grafting was obtained from electrospray mass spectrometry for products formed from reactions with glucosamine (the monomeric unit of chitosan) and the model dipeptide Tyr-Ala. When this model dipeptide was incubated with tyrosinase and chitosan, there was a marked increase in the viscosity of the solution. This viscosity increase provides physical evidence that tyrosinase can initiate peptide grafting onto the chitosan backbone. A peptide-modified chitosan derivative was generated by reacting chitosan (0.32 w/v%) with acid-hydrolyzed casein (0.5 w/v %) using tyrosinase. After reaction, the peptide-modified chitosan was partially purified and dissolved in an aqueous acetic acid solution. Low concentrations of this peptide-modified chitosan were observed to confer viscoelastic properties to the solutions. Specifically they conferred high viscosities and shear thinning properties to the solutions, and solutions containing only 1 w/w % of the peptide-modified chitosan behaved as weak gels. Thus, tyrosinase provides a simple and safe way to convert food-processing byproducts into environmentally friendly products that offer useful functional properties. The selectivity of tyrosinase and the relatively high reactivity of chitosan's amines allow grafting to be performed with uncharacterized peptide mixtures present in crude hydrolysates.
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PMID:Enzymatic grafting of peptides from casein hydrolysate to chitosan. Potential for value-added byproducts from food-processing wastes. 1496 32

Epidemiologic studies suggest that dietary complex carbohydrates are protective against colorectal cancer but dietary protein may increase risk. However, experimental data to support these relationships are scant. We have shown in rats that consumption of a high-protein (25% casein) diet for 4 wk resulted in a twofold increase in damage to colonocyte DNA compared with a low-protein (15% casein) diet. This was associated with thinning of the colonic mucous barrier and increased levels of fecal p-cresol. Addition of resistant starch as a high-amylose maize starch to the diet increased cecal short-chain fatty acid pools and attenuated DNA damage, suggesting protection against genotoxic agents. In humans, this could translate to altered risk of colonic cancer.
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PMID:Resistant starch attenuates colonic DNA damage induced by higher dietary protein in rats. 1574 29

Small micellar casein particles, so-called submicelles, were obtained by removing colloidal calcium phosphate from native casein by adding sodium polyphosphate. Aqueous submicelle suspensions were characterized using light scattering and rheology as a function of concentration and temperature. The casein submicelles behave like soft spheres that jam at a critical concentration (C(c)) of about 100 g L(-1). The viscosity does not diverge at C(c), but increases sharply, similarly to that of multiarm star polymers. C(c) increases weakly with increasing temperature, which leads to a strong decrease of the viscosity close to and above C(c). Concentrated submicelle suspensions show strong shear-thinning above a critical shear rate and the shear stress becomes independent of the shear rate. The critical shear rates at different temperatures and concentrations are inversely proportional to the zero-shear viscosity. At much higher shear rates, the shear stress fluctuates strongly in time indicating inhomogeneous flow. The frequency dependence of casein submicelle suspensions is characterized by elastic behavior at high frequencies (concentrations) and viscous behavior at low frequencies (concentrations).
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PMID:Dynamic mechanical properties of suspensions of micellar casein particles. 1592 12

In a previous study we have shown that high levels of dietary protein (as casein) result in increased levels of colonic DNA damage, measured by the comet assay, and thinning of the colonic mucus layer in rats when dietary resistant starch (RS) is negligible. Feeding RS abolishes these effects. This study aimed to establish whether a diet high in protein as cooked red meat would have similar effects and whether RS was protective. Rats were fed a diet containing 15% or 25% casein or 25% cooked lean red beef, each with or without the addition of 48% high amylose maize starch (a rich source of RS) for four weeks. As expected, high dietary casein caused a 2-fold increase in colonic DNA damage compared with a low casein diet and reduced the thickness of the colonic mucus layer by 41%. High levels of cooked meat caused 26% greater DNA damage than the high casein diet but reduced mucus thickness to a similar degree to casein. Addition of RS to the diet abolished the increase in DNA damage and the loss of colonic mucus thickness induced by either high protein diet. Cecal and fecal short chain fatty acid pools were also increased by inclusion of RS in the diet. Because DNA damage is an early step in the initiation of cancer, these findings suggest that increased DNA damage due to high dietary protein as cooked red meat or casein could increase colorectal cancer risk but inclusion of resistant starch in the diet could significantly reduce that risk.
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PMID:Resistant starch prevents colonic DNA damage induced by high dietary cooked red meat or casein in rats. 1662 72

Previous studies have shown increased levels of colonocyte DNA damage (as measured by the comet assay) and thinning of the colonic mucus layer in rats fed higher dietary protein as casein or red meat with highly digestible starch. Feeding resistant starch (RS) as high amylose maize starch (HAMS) opposed these changes. However, the dietary level of HAMS was relatively high (48% by weight) so this study was conducted to establish whether HAMS had the same effects at lower dietary levels. Adult male rats were fed a diet containing 25% casein with 0%, 10%, 20%, 30% or 40% HAMS for 4 wk. DNA single strand breaks and 8-hydroxyguanosine levels were measured in isolated colonocytes by the comet assay. As expected, comet tail moment was greatest and the mucus barrier thinnest in rats fed 0% HAMS. DNA damage was reduced and the mucus barrier thickened in a logarithmic dose-dependent manner by HAMS. There was no significant difference in 8-hydroxyguanosine between dietary groups. Caecal and fecal short chain fatty acid (SCFA) pools rose with the increased level of dietary HAMS. DNA damage of colonocytes correlated negatively with caecal SCFA but the strongest correlation was with caecal butyrate, which is consistent with the proposed role of this SCFA in promoting a normal cell phenotype. These data show that HAMS prevents protein-induced colonic DNA damage in a dose-dependent manner. Inclusion of 10% HAMS was found to be sufficient to oppose colonocyte DNA damage, and to increase caecal and fecal SCFA pools.
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PMID:Dose-dependent reduction of dietary protein-induced colonocyte DNA damage by resistant starch in rats correlates more highly with caecal butyrate than with other short chain fatty acids. 1742 35

Understanding the mechanisms involved in structural development in the vicinity of membrane constitutes a considerable challenge in the improvement of ultrafiltration process in industrial applications. In situ small-angle X-ray scattering (SAXS) performed with custom-made ultrafiltration cell has permitted the structural arrangement to be probed and concentration profiles to be obtained in deposited layers during frontal filtration of casein micelle suspension. SAXS allowed the structure of the accumulated layers of casein micelles between 280 microm and 1 mm from the membrane surface to be followed at length scales from a few nanometers to about 100 nm. These results have been combined with hydrodynamic measurements (permeation flux) and rheological investigations. Under frontal filtration, the time dependence of concentration at different distances from the membrane surface has been obtained. This temporal evolution is marked by an exponential increase of the concentration followed by a slower growth which has been associated with a change in the rheological behavior of the suspension from Newtonian to shear thinning behavior.
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PMID:Spatial and temporal in situ evolution of the concentration profile during casein micelle ultrafiltration probed by small-angle X-ray scattering. 1844 23

Sodium caseinate is derived from casein which is the major milk protein and forms small star-like aggregates in aqueous solution. The dynamic mechanical properties of dense sodium caseinate suspensions were studied by measuring the shear viscosity and the frequency dependent loss and storage shear modulus. The viscosity is shown to increase strongly above a concentration, C(c), due to jamming of the aggregates. C(c) depends little on the pH or on the ionic strength. The repulsion between the aggregates increases with decreasing temperature leading to jamming at lower concentrations. As a consequence the viscosity decreases strongly with increasing temperature for concentrated suspensions. The frequency dependent shear modulus of concentrated suspensions shows a solid like behaviour at high frequencies. Shear thinning is observed at Peclet numbers larger than unity.
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PMID:Structure and dynamical mechanical properties of suspensions of sodium caseinate. 1867 76


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