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At least 811 records · Page 45Linked to original sources
PubMed2003

Viscosity of rice flour: a rheological and biological study.

Rice breeders frequently use rapid visco analysis (RVA) as in index of rice quality. Potentially, viscosity curves could also be used to predict the sensory properties of a sample of rice or the processing properties of rice when used as an ingredient. The aim of this study is to determine the contribution of the main components of rice flour-starch and protein polymers and lipids-to the viscosity curve, accounting for biological and rheological contributions, and interactions with water. By deconstructing the rice flour, resistance to shear is generally the primary factor that affects rheological processes in the RVA, often masking the physical processes of cooking. Thus, higher concentrations of water reveal more about the true biological and physical processes of the transition from a powder to paste. Proteins contribute to peak height, offset thixotropy, and contribute to the final viscosity. Starch-lipid complexes can mask differences in the molecular structures of amylose and amylopectin, and removing lipids alters the structure of the paste significantly, which consequently alters viscosity curves.

Amylose↗
PubMed2003

Changes in macroscopic viscosity do not affect the release of aroma aldehydes from a pectinaceous food model system of low sucrose content.

The effects of pectin and viscosity on the release of a systematic series of aldehydes (alkanals, methyl-alkanals, alkenals, and alkandienals) were studied in a food model system of low sucrose content (10% w/w). The viscosity was varied by adding different amounts of Ca(2+) (0, 13.5, and 27 mg/g pectin) to the model system of constant pectin concentration (0.4% w/w). Air-liquid partition coefficients, K (37 degrees C), of the aroma compounds were determined in aqueous and pectin-thickened solutions. Diffusivities of the aroma compounds in water and three pectin-thickened solutions were estimated from release rate constants that were obtained via timed collection of volatiles in the gas phase and quantifications by dynamic headspace-gas chromatography. The partition coefficients increased as the carbon chain increased within each homologous series. Overall, no significant difference was found between partition coefficients of aldehydes in water and in pectin solutions except for 2-methyl-propanal and butanal that showed higher K values when pectin was present. Furthermore, the diffusional properties of the model system with a constant pectin level (0.4% w/w) remained constant when the viscosity was increased from 0.001 to 150 Pa s. It was concluded that neither pectin nor alterations in macroscopic viscosity as such influenced the release of aldehydes from the pectin-thickened food model system.

Aldehydes↗
PubMed2006

Flavored yogurt complex viscosity influences real-time aroma release in the mouth and sensory properties.

The influence of flavored yogurt texture on aroma perception and in-nose aroma release measured by atmospheric pressure chemical ionization mass spectrometry analysis was investigated. The study was carried out on six yogurts varied by protein composition and mechanical treatment. For the same matrix composition, the complex viscosity of yogurts influenced in-nose release and perception. After swallowing, aroma release and intensity of olfactory perception were stronger in low-viscosity yogurts than in high-viscosity yogurts. Moreover, the protein composition influenced aroma release only when yogurts exhibited wide variations of complex viscosity and consequently texture. In mouth, aroma release and perception were influenced more by yogurt mechanical treatment than by protein composition. On the basis of mass transfer analysis, the main physical mechanism which could explain the difference in aroma release would be the surface exchange area developed in the mouth and in the throat.

Dietary Proteins↗
PubMed2005

Interfacial dilatational elasticity and viscosity of beta-lactoglobulin at air-water interface using pulsating bubble tensiometry.

The ability of proteins to provide stability in foams is greatly influenced by their interfacial dilatational rheological properties. Surface tension response of a pulsatingbubble with an adsorbed layer of beta-lactoglobulin was measured for different frequencies and protein concentrations using a pulsating bubble tensiometer. A methodology, accounting for adsorption/desorption as well as variation of surface concentration due to expansion/contraction, was developed for the evaluation of surface dilatational elasticity and viscosity at different frequencies from these measurements. The adsorption rate constants were inferred from the surface pressure dynamics of protein adsorption using a Langmuir minitrough. The desorption rates were shown to be negligible for beta-lactoglobulin from the surface pressure response of a spread monolayer when subjected to compression in a Langmuir minitrough. The proposed model was employed to infer the interfacial dilatational viscosity and elasticity of an adsorbed beta-lactoglobulin layer at the air-water interface from experimental pulsating bubble data for protein concentrations in the range of 0.01-0.5 wt % at pH 7. As expected, the interfacial dilatational rheological properties were found to be higher at higher protein concentrations, this effect being less pronounced for dilatational elasticity. Heating at 80 degrees C for 30 min was found to result in higher interfacial dilatational viscosity and lower interfacial dilatational elasticity though this difference was within experimental error. The traditional approach for the inference of interfacial dilatational rheological properties is found to overpredict the interfacial dilatational elasticity whereas the viscosity values do not differ significantly from those obtained using the current analysis.

Adsorption↗
PubMedDate not supplied

Trehalose-enzyme interactions result in structure stabilization and activity inhibition. The role of viscosity.

Stress resistance is essential for survival. The mechanisms of molecule stabilization during stress are of interest for biotechnology, where many enzymes and other biomolecules are increasingly used at high temperatures and/or salt concentrations. Diverse organisms, exhibit rapid synthesis and accumulation of the disaccharide trehalose in response to stress. Trehalose is also rapidly hydrolyzed as soon as stress ends. In isolated enzymes, trehalose stabilizes both, structure and activity. In contrast, at optimal assay conditions, trehalose inhibits enzyme activity. A general mechanism underlying the trehalose effects observed at all temperatures probably is the trehalose-mediated increase in solution viscosity that leads to protein domain motion inhibition. This may be analyzed using Kramer's theory. The role of viscosity in the effects of trehalose is analyzed in examples from the literature and in studies on the plasma membrane H(+)-ATPase from Kluyveromyces lactis. In the cell, it may be proposed that the large concentration of trehalose reached during stress stabilizes structures through viscosity. However, once stress ends trehalose has to be rapidly hydrolyzed in order to avoid the viscosity-mediated inhibition of enzymes.

Enzymes↗
PubMed2003

Suppressive effect of viscous dietary fiber on elevations of uric acid in serum and urine induced by dietary RNA in rats is associated with strength of viscosity.

This study was performed to clarify how dietary fiber (DF) with different viscosities would be associated with dietary RNA metabolism. Male Wistar strain rats, four weeks old, were fed diets containing a 3% (w/w) yeast RNA and a 5% (w/w) viscous DF for five days. Viscosity of DF samples used, in order of strength, were xanthan gum (XG) > guar gum (GG) > locust bean gum (LBG) > karaya gum (KG) > pectin (PE) = arabic gum (AG) > CM-cellulose (CMC) = inulin (IN). The serum uric acid concentration in the viscous DF groups significantly decreased as compared with that in the cellulose (CL) group. The urinary excretions of uric acid and allantoin in the respective groups given AG, GG, IN, KG, PE, and XG were significantly suppressed as compared with those in the CL group. The fecal RNA excretion was markedly increased in the IN, KG, PE, and XG groups in comparison to the CL group. The DF with high viscosity significantly suppressed RNA digestion by RNase A and decreased uptakes of 14C-labeled adenosine and adenosine 5'-monophosphate (5'-AMP) in rat jejunum. The results reveal that the suppressive effect of DF on elevation of serum uric acid concentration induced by dietary RNA in rats is associated with the strength of DF viscosity. The mechanism by which this is accomplished is suggested to be attributed to the inhibitions of digestion for dietary RNA and/or absorption of the hydrolyzed compounds.

Adenosine Monophosphate↗
PubMed2000

Assessment of the viscosity of the pulmonary artery wall.

Large artery wall viscosity reduces the efficiency of heart/vessel coupling. The aim of the present study was to assess pulmonary artery wall viscosity through comparison of the static (Dst) and dynamic distensibility (Ddyn) of the vessel wall. Right pulmonary artery pressure and diameter was measured in 13 patients and eight healthy volunteers. Ddyn was calculated as the relative change in end-diastolic diameter induced by the pressure pulse, and Dst as the relative change in mean diameter induced by the change in mean pressure during steady-state exercise. Dst did not differ significantly from Ddyn (mean+/-SD 22.8+/-19.2 versus 21.0+/-18.3 10(-3) mmHg(-1)), as tested by paired t-test and analysis of covariance, with age as covariant. End-diastolic diameter increased, whereas Dst and Ddyn decreased as a function of age (r=-0.69 and -0.67, respectively; p<0.01 for both). Ddyn did not change from rest to exercise in spite of a 23+/-16-beats-min(-1) increase in cardiac frequency. Pulmonary artery wall viscosity was negligible and no increase in wall viscosity occurred during cardioacceleration.

Adult↗
PubMed2003

Nanoscale effects leading to non-Einstein-like decrease in viscosity.

Nanoparticles have been shown to influence mechanical properties; however, transport properties such as viscosity have not been adequately studied. This might be due to the common observation that particle addition to liquids produces an increase in viscosity, even in polymeric liquids, as predicted by Einstein nearly a century ago. But confinement and surface effects provided by nanoparticles have been shown to produce conformational changes to polymer molecules, so it is expected that nanoparticles will affect the macroscopic viscosity. To minimize extraneous enthalpic or other effects, we blended organic nanoparticles, synthesized by intramolecular crosslinking of single polystyrene chains, with linear polystyrene macromolecules. Remarkably, the blend viscosity was found to decrease and scale with the change in free volume introduced by the nanoparticles and not with the decrease in entanglement. Indeed, the entanglements did not seem to be affected at all, suggesting unusual polymer dynamics.

Diffusion↗
PubMed2002

Viscosity-independent velocity of neutrophils rolling on p-selectin in vitro or in vivo.

OBJECTIVE: To determine whether selectin-mediated leukocyte-rolling velocity in inflamed venules in vivo is determined by wall shear rate (WSR) or by wall shear stress (WSS). METHODS: WSS was manipulated independently of WSR by altering the viscosity of blood plasma in mice with an isovolemic exchange of blood for low- or high-viscosity dextran solutions. Rolling of neutrophils or beads coated with P-selectin glycoprotein ligand-1 (PSGL-1) was reconstituted on P-selectin immobilized on the wall of a parallel plate flow chamber at two different viscosities of the perfusion medium. RESULTS: Leukocytes in vivo showed no increase in rolling velocity when shear stress was doubled by doubling viscosity. Neutrophils in the parallel-plate flow chamber in vitro showed the same dependence on WSR as leukocytes in vivo, but bead-rolling velocities correlated best with WSS. Rolling leukocytes, but not beads, deformed significantly in shear flow, and deformation correlated better with WSS. CONCLUSION: These data suggest leukocyte deformation during rolling offsets increased bond breakage at higher shear stress. The stable rolling velocity allows sufficient surveillance of the endothelial surface, even in venules with high WSS. doi:10.1038/sj.mm.7800165

Animals↗
PubMed1978

Enhancement of the viscosity of mucin by serum albumin.

The interaction of serum albumin with a model epithelial mucin from pig stomach was explored by rotary viscometry. During 30 min of incubation of human serum albumin(20mg/ml) and pig gastric mucin (8mg/ml) in iso-osmotic buffers at 37 degrees C, the solution became markedly viscous. Viscosity enhancement was proportional to albumin concentration (2-40mg/ml), was most pronounced under conditions of low shear rate (less than 45S-1), and was considerably greater than the additive or multiplicative viscosity values calculated from albumin or mucin solutions measured separately. The viscous mucin-albumin complex was destroyed by high shear rates (greater than 90S-1), but slowly re-formed under zero shear conditions. Elevation of pH (7 to 9), ionic strength (0.1 to 1.0), and addition of disodium EDTA (5mM) did not cause marked or specific alterations in the viscosity of the mixture, suggesting that electrostatic interactions probably do not stabilize mucin-albumin complexes. Urea (7M) and heating (35 to 55 degrees C) caused a major increase in the viscosity of mucin and mucin-albumin mixtures, suggesting that rupture of hydrogen bonds, unfolding and partial denaturation of mucin promotes greater intertangling (possibly hydrophobic interactions) between mucin and albumin molecules. The implications of mucin-albumin interaction in diseases associated with mucus obstruction are briefly discussed.

Animals↗
PubMed1983

Effect of pH, viscosity and ionic-strength changes on ciliary beating frequency of human bronchial explants.

1. Ciliary activity is significantly influenced by chemical and physical properties of the liquid medium in which the cilia beat. 2. We studied the effect of changes in pH, ionic strength and viscosity on the ciliary beat frequency (CBF) of explants of human respiratory mucosa. 3. Optimal CBF was elicited at pH 7 . 0-9 . 0, with a marked reduction of CBF outside these limits. The CBF was well preserved at NaCl concentrations between 5 g/l (80 mmol/l) and 12 g/l (200 mmol/l), but there was rapid loss at concentrations below 0 . 5 g/l (10 mmol/l). The cilia beat best at viscosities below 1 . 0 centipoises (1 mN s m-2). Increase of the viscosity gradually decreases CBF with a significant drop at viscosities above 87 millipoises. 4. It is concluded that the above limits may fairly accurately indicate the actual physical characteristics of the periciliary environment ('sol layer') in vivo.

Bronchi↗
PubMed2004

Effects of age, gender, bolus volume, bolus viscosity, and gustation on swallowing apnea onset relative to lingual bolus propulsion onset in normal adults.

The purpose of this study was to ascertain the normal relation of swallowing apnea (SA) onset relative to lingual bolus propulsion along with factors that may alter this relation. Forty adults, composed of 10 men and 10 women in each of 2 age groups (i.e., 20-30 and 63-79 years) participated. SA onset was assessed during 5- and 20-ml bolus volumes of water and apple juice across 3 trials. The effects of age, gender, bolus volume, bolus viscosity, and gustation on SA onset relative to lingual bolus propulsion were examined. A significant interaction of Age x Gender x Volume was found. In general, older adults initiated SA onset earlier than young adults, and large boluses elicited an earlier SA onset than small boluses regardless of group. Young men demonstrated significantly later SA onset than the older men for large volumes; this difference was not observed for small volumes, nor was it found between young and older women. SA onset also was assessed during 5-ml bolus volumes of thin apple juice, thick apple juice, and applesauce across three trials. A significant main effect of viscosity was found revealing that SA onset was initiated later as bolus viscosity increased. Thus, the results of this investigation provided data on the relation of SA onset relative to lingual bolus propulsion in individuals with normal swallowing and how this relation changes as a function of age, gender, bolus volume, bolus viscosity, and gustation.

Adult↗
PubMed1994

Pharyngeal effects of bolus volume, viscosity, and temperature in patients with dysphagia resulting from neurologic impairment and in normal subjects.

The oropharyngeal swallow of 10 patients with mild dysphagia at 3 weeks after a cerebrovascular accident (stroke), 10 normal subjects, and 8 neurologically impaired patients with moderate to severe dysphagia was studied videofluorographically to examine the effects of 2 bolus temperatures (room temperature and 33 degrees F), 2 volumes, and 2 viscosities on the durations of pharyngeal stage swallow events and the frequency and nature of oropharyngeal swallowing problems and bolus transit. Normal subjects exhibited significantly longer pharyngeal response times and longer laryngeal elevation only for 1 ml cold liquid. The stroke patients and the 8 significantly dysphagic neurologically impaired patients exhibited very few significant effects of temperature on swallowing disorders or swallow measures. Increases in bolus volume and viscosity decreased pharyngeal delay times in both neurologically impaired patient groups. Stroke patients exhibited significantly longer pharyngeal delay times but shorter pharyngeal response times, laryngeal closure, cricopharyngeal opening, and laryngeal elevation than normal subjects on some bolus volumes and viscosities. Results are discussed in terms of the potentially therapeutic effects of bolus volume and viscosity.

Adolescent↗
PubMed2000

Effects of dietary fibre and olestra on regional apparent viscosity and water content of digesta residue in porcine large intestine.

BACKGROUND: Increased consumption of non-digested, non-absorbed substrates, such as dietary fibre, can lead to an increase in colonic transit rate and stool output. The effects of dietary fibre and olestra on the consistency and water content of digesta residue within the large bowel were not known. AIM: The aim of this study was to determine the effects of dietary fibre and olestra on regional dehydration and apparent viscosity of digesta residue throughout the large bowel. METHODS: Seventy-eight pigs were fed diet alone (control) or supplemented with 40 g/day or 80 g/day dietary fibre or olestra and sacrificed 24, 48, 96 or 192 h after initiation of dosing. The large bowel was removed, divided into 13 segments, and the digesta residue/stool was analysed for apparent viscosity (peak force for extrusion) and percentage water content. RESULTS: In control animals, digesta residue occurred as a continuum, from liquid in the cecum (87.9% water) to solid in the rectum (71. 5% water). The relatively small decrease in percentage water content (16.4%) resulted in a marked increase in mean apparent viscosity (liquid = 87 g peak force; solid=3919 g peak force). Dietary fibre increased the percentage water content of digesta residue throughout the large bowel. In contrast, olestra decreased the percentage water content of digesta residue in the mid and distal large bowel. At 40 g/day, dietary fibre showed a significant (P < 0.05) digesta residue/stool softening effect for all time points, beginning at 24-h (single dose). Olestra 40 g/day did not significantly soften digesta residue/stool until 48 h (2 doses, P < 0.05), and was not different from control at 96 h. At 80 g/day, both dietary fibre and olestra significantly (P < 0.01) softened digesta residue/stool at all time points. There were no liquid or oily stools at any dose or time-point. CONCLUSIONS: Relatively small changes in water content result in large changes in digesta residue/stool apparent viscosity. Dietary fibre increased digesta residue/stool water content throughout the bowel, resulting in softer digesta residue/stool. In contrast, olestra decreased stool water content, yet had a similar stool softening effect compared to dietary fibre.

Animals↗
PubMed2002

DTG thermal analyses and viscosity measurements of three commercial agar impression materials.

Three commercial agar impression materials, two for clinical uses and one for dental laboratory, were examined for their thermal properties by differential thermogravimetric (DTG) thermal analyses and viscosity measurements. On DTG profiles, an endothermic peak along with weight loss at around 100 degrees C was observed on all three agar impression materials as a result of water evaporation. Two clinical agar impression materials were more susceptible to this trend than the remaining one dental laboratory agar impression material. The viscosity of three agar impression materials could be expressed in the exponential function of temperature. Viscosity at 46 degrees C of one dental laboratory agar impression material far exceeded those of two clinical agar impression materials. Monitoring the viscosity could facilitate the detailed analysis of setting process of agar impression materials upon cooling, and might be useful for future development of agar-based dental impression materials.

Agar↗
PubMed2002

Acidosis induced by lactate, pyruvate, or HCl increases blood viscosity.

PURPOSE: Serum lactate correlates with the severity of disease and the mortality in shock. It is not clear if lactate is only a marker or a mediator of disease. We tested the hypothesis that acidosis induced by lactate and pyruvate affects blood flow properties. MATERIALS AND METHODS: Human blood was incubated with additional lactate (0-50 mmol/L) or pyruvate (0-25 mmol/L) for 1 hour at 37 degrees C. Blood viscosity was measured at high (94.5 s(-1)) and low (0.1 s(-1)) shear rate. Hematocrit was measured with an electronic particle counter as well as centrifugation. RESULTS: A total of 50 mmol/L additional lactate produced acidosis (pH 6.4) and increased whole-blood viscosity at high shear rate (94.5 s(-1): 6.53 +/- 0.51 mPa.s vs 4.94 +/- 0.18 mPa.s for control, n = 5, P <.001) and low shear rate (0.1 s(-1): 93.9 +/- 18.6 mPa.s vs 53.5 +/- 7.7 mPa.s, n = 5, P <.001). Simultaneously, an increased centrifuged hematocrit was observed (about 7% with 50 mmol/L lactate, P <.001), indicating eryth-rocyte swelling. These changes were reversible on removal of lactate. The addition of 25 mmol/L pyruvate also induced acidosis and increased blood viscosity and centrifuged hematocrit. When HCl was used to induce a comparable pH level decrease, a similar increase in blood viscosity and hematocrit were observed. CONCLUSIONS: Pronounced acidosis induced by either lactate, pyruvate, or HCl impairs blood flow properties, which may contribute to the understanding of the pathophysiology of critical illness.

Acidosis↗
PubMed1988

Blood viscosity after a 1-h submaximal exercise with and without drinking.

Ten healthy subjects performed two exercise sessions similar to an endurance training session for average athletes (1 cycling exercise at 85% of the maximal heart rate on a Monark cycle ergometer). In the first session, the subjects were not allowed to drink during exercise. During the second session, the same subjects performed the same exercise as during the first session but they drank a beverage volume equal to the weight loss induced by the first exercise session to verify the hypothesis that the compensation of sweat loss by drinking could attenuate the exercise-induced blood viscosity increase. Both protocols (with and without drinking) induced a significant increase of hematocrit and plasma viscosity. The whole blood viscosity increased at all shear rates but this increase was significant only for the exercise protocol without drinking. Blood thixotropic property, erythrocyte deformability, and erythrocyte aggregability remained unchanged after both exercise protocols. Hemoconcentration explained the increase of hematocrit and plasma viscosity. Hemoconcentration was probably the consequence of a filtration process through capillary leakage in addition to sweat loss, which could explain the partial effect of drinking in our study.

Adult↗
PubMed1995

[Postoperative intraocular pressure in the first days after intraocular administration of hyaluronic acid solution with different viscosities].

BACKGROUND: Viscoelastic substances are used in anterior segment surgery to reduce tissue trauma and endothelial cell loss and to serve as space maintainer. Healon GV (approximately greater viscosity), a hyaluronic acid product with a ten times higher viscosity than Healon, is utilized in complicated procedures (vitreous pressure, flat anterior chamber, congenital cataracts, etc.) and often in phacoemulsification. Intraocular pressure (IOP) rise following incomplete removal is a known problem. MATERIALS AND METHODS: A prospective randomized study was performed to evaluate the IOP following cataract surgery with Healon or Healon GV and different removal times (RT). Forty patients (forty eyes) having uncomplicated phacoemulsification with foldable silicone posterior chamber lens implantation and identical viscoelastic removal technique were assigned to four groups: Healon with 20 or 40 seconds (sec.) RT, Healon GV with 20 or 40 sec. RT. All surgeries were performed by the same surgeon using the same technique especially for the removal of the viscoelastic. All patients had an identical pre- and postoperative medication. Intraocular pressures were obtained using Goldman's applanation tonometry preoperatively, six, 24, 36, and 48 hours postoperatively. RESULTS: The IOP follow-up showed no significant difference between the two viscoelastic substances and the two different removal times of 20 and 40 sec. (t-test). In four patients (two of the Healon-groups, two of the Healon GV-groups) the IOP required treatment. On the second postoperative day, the same four patients showed IOP lower than 22 mm Hg. The highest mean-IOP (mm Hg) in both Healon-groups was obtained at 24 hours postoperatively: 18.5 +/- 3.9 SD (Healon); 17.3 +/- 5.9 SD (Healon GV). CONCLUSION: The incidence of postoperative rise in IOP using high viscosity hyaluronic acid (Healon GV) can be minimized by the applied removal technique. Both viscoelastics-despite of higher molecular weight and viscosity-can be removed equally from the anterior chamber following phacoemulsification and posterior chamber lens implantation utilizing IOP as a parameter in vivo.

Aged↗