Gel Firmness Research Articles

Studies on Rheological Properties of Stirred Milk Gels Made from Milk with Defined Genetic Variants of κ-Casein and β-Lactoglobulin

The rheological properties of acidified milk gels made from milk with defined genetic variants of κ-casein and β-lactoglobulin have been investigated. Gels were prepared from skim milk after heating for 4 min at 90°C by acidification with glucono-δ-lactone and gentle stirring after holding for 24 h at 20°C. Stirred acidified milk gels were then kept at 6°C for 96 h and thereafter measured for the rheological properties using a Bohlin VOR Rheometer. The milk gels containing only the B variant of β-lactoglobulin (homozygous cows) were found to have a significantly higher elastic modulus as compared to milk gels containing both β-lactoglobulin A and B or only A. An explanation could be that more β-lactoglobulin B had aggregated with the casein micelles, since a strong correlation was found between the loss of native β-lactoglobulin in the milk serum and the gel firmness. No correlation was found between gel firmness and any of the κ-casein genetic variants, dry matter content and the total protein concentration, respectively. Furthermore, viscous properties did not vary between the acidified milk gels in this experiment.

Effects of Salts on the Properties of Sols and Gels Prepared from Whey Protein Isolate and Process Whey Protein

Process whey protein was prepared by heat treatment of whey protein isolate under salt-free conditions. Addition of sodium chloride, trisodium cit-rate, potassium chloride, or calcium chloride to a process whey protein solution increased the viscosity and resulted in gelation at 25°C. In contrast, the viscosity of whey protein isolate solutions was not changed. The properties of whey protein isolate and process whey protein gels prepared by heating at 80°C for 60min with 25 different salts were measured and compared. Although process whey protein produced gels with the addition of any of the salts examined, whey protein isolate solution did not gel with some salts. The tendency of both protein solutions to gel apparently depended on the lyotropic nature of the cation. Inorganic salts produced firmer gels than did organic salts. The gel strength and water-holding capacity of both proteins decreased as salt concentration increased. When the transparent gels prepared from process whey protein were heated again, the gel firmness increased, adhesiveness decreased, and transparency and cohesiveness slightly decreased, depending on the temperature and duration of the second heating.

Cross-Linkage of Canavalia ensiformis Starch with Adipic Acid: Chemical and Functional Properties

Adipic acid behavior was studied as a cross-linkage agent for Canavalia ensiformis native starch. A 23 factorial design with two replicates of each treatment was utilized. Acid concentration (1 and 2%) and the chemical agent incorporation method (direct incorporation with an initial pH adjustment, direct addition with pH readjustment, and 3% NaOH simultaneous addition) were the factors utilized. Gel firmness and syneresis were used as response variables. Main factors and their interactions showed statistical influence (P < 0.05) over the cross-linkage level achieved; the most effective modification was obtained by reactant direct incorporation. Cross-linkage increased gel firmness (11.25 mm penetration) compared to native starch (14.75 mm penetration), diminished syneresis to 7.15 mL/50 mL, and reduced solubilization and swelling power to 18% and 28.04 g/g levels, respectively. Keywords: Cross-linked; starch; Canavalia ensiformis; adipic acid; functional properties

Annealing induced gelation of xanthan/water systems

The effect of annealing at a temperature higher than the gel-sol transition temperature on the junction formation in the gelation process of xanthan/water solutions was investigated by the falling ball method (FBM) and differential scanning calorimetry (d.s.c.). Aqueous solutions of xanthan dissolved at room temperature were inhomogeneous. Although gel-like solutions were formed after subsequent cooling, the solutions could not be categorised as a gel. In contrast, when the solutions were annealed at 40°C, firm gels were formed by subsequent cooling. The gel-sol transition temperature ( T g-s) was clearly observed by FBM. It was found that T g-s gradually increased from 27°C with increasing annealing time and approached a constant value, i.e. 33°C for 1 wt% sample and 40°C for 2 wt% sample. The annealing time, where T g-s levelled off, depended on sample concentration and annealing temperature. During annealing from 0 to 12 h, it was observed that the amount of non-freezing water estimated by d.s.c. fluctuated, although a steady increase of T g-s was observed by FBM. This phenomenon is interpreted as a homogenisation of the solution, i.e. xanthan molecules become free from their molecular assembly through desorption of non-freezing water by annealing. The above results indicate that xanthan/water solutions form the gel state when they are fully annealed in the sol state.

Utilization of fluted pumpkin fruit (Telfairia occidentalis) in marmalade manufacturing.

Marmalade was produced from fluted pumpkin (Telfairia occidentalis) fruit. The fruit was pulped, boiled and filtered to obtain pectin extract. The extract was boiled at 102 degrees C for 30 min with the pH and sugar levels adjusted to 3.2 and 68.5 degrees Brix, respectively. Fruit shreds were added towards the end of boiling. Results of analyses showed that the pulp is rich in Na, K, Fe, P, Mn and pectin (1.01%), but low in protein (0.86%). The marmalade had a firm gel and was acidic (pH 3.15). Mold was absent and syneresis did not occur. The marmalade contained 68.5% total soluble solids and set at 52-56 degrees C. Sensory evaluation showed no significant difference (p = 0.05) in taste, consistency, spreadability and overall acceptability between fluted pumpkin marmalade and commercial orange marmalade. Both chemical and sensory results denote that the marmalade was highly desirable and compared favourably with similar preserves produced in Nigeria.

Transposition simple des gros vaisseaux. Physiopathologie, prise en charge actuelle

Response Surface Methodology (RSM) was adopted to optimize the preparation of NZ hoki (Macruronus novaezelandiae) gelatine gels treated with Transglutaminase (TGase) and some of the rheological properties were characterized. The optimum concentration of the enzyme [X1] was 3.33 mg/g, incubation time, [X2] was 30 min, and incubation temperature, [X3] was 37 °C. The calculated gel strength achieved by RSM was in very good agreement with the experimental value. The addition of TGase to hoki gelatine at the optimum concentration of increased the gel strength from 197 ± 5 g to 278.2 ± 0.19 g and the melting point from 21.4 ± 0.8 °C to 25.9 ± 0.1 °C. The increase in the G' values with the addition of TGase indicated the formation of firmer gels and the changes in G' and G" values with increase in temperature showed increase in melting point.

Effect of gelation on the chemical stability and conformation of leuprolide.

The purpose of this study was to characterize the conformation, aggregation, and stability of leuprolide on gelation. Infrared spectra (FTIR) of leuprolide solutions and gels were collected in water, propylene glycol (PG), dimethyl sulfoxide (DMSO), and trifluoroethanol (TFE). Leuprolide solution and gel stability data were obtained by SEC and RP-HPLC. Leuprolide was induced to gel with increasing peptide concentration, introduction of salts, and gentle agitation. Leuprolide dissolved in water (400 mg/ml) demonstrated FTIR spectra consisting of two major bands of equal intensity at 1615 cm(-1) and 1630 cm(-1), similar to inter- and intra-molecular beta-sheet structure in proteins. When samples were gently agitated for 24 hours at 25 degrees C, the formulation was observed to change from a viscous liquid to an opaque gel with a concomitant shift in infrared spectra from the equal intensity bands to mostly 1630 cm(-1), indicating a shift to a preferred beta-sheet structure. Incubation of leuprolide with 20-200 mM salts at 25 degrees C and 37 degrees C also produced gels ranging from clear to cloudy and stringy white precipitates. The gel and precipitate were marked by a shift of the predominant beta-sheet band to 1630 cm(-1) and 1615 cm(-1), respectively. Leuprolide was also observed to gel and/or precipitate in mixtures of water, PG or TFE, but not in DMSO. Birefringence was noted in many of the firmer gels. Both solutions and gels demonstrated minimal dimer or trimer formation, with no larger order aggregates detected. The chemical stability profile of gelled leuprolide was similar to that of the non-gelled water formulation by RP-HPLC.

Viscoelastic Properties of Xanthan Gels Interacting with Cations

ABSTRACTViscoelastic properties of gels were greatly affected by xanthan gum concentration and types of cations. The storage moduli (G'), measured at 1.0 Hz, were 8.3, 10, and 2700 Pa for xanthan gels at 0.5% polymer concentration and 37, 42, and 13000 Pa for xanthan gels at 1.0% polymer concentration in the presence of Na+, Ca2+, or Fe3+, respectively. The elastic recovery was 27.9, 61.6, and 66.3% for 0.5% xanthan gels, and 38.5, 22.5, and 69.1% for 1.0% xanthan gels, in the presence of Na+, Ca2+, or Fe3+, respectively. The generalized Kelvin model simulated creep compliance and ferric ion was an excellent crosslinker for a rigid, firm gel.

Relationships between Functional Attributes and Molecular Structures of Amylose and Amylopectin Fractions from Corn Starch

Understanding starch structure−function relationships is vital to the continued development for new uses for starch. Fractionated corn amylose and amylopectin, with known molecular weights, chain lengths, and branching and crystalline ratios, were studied for pasting, gel textural, and retrogradation properties by rapid viscoanalysis, textural profile analysis, and differential scanning calorimetry. Amylose fractions with weight-average molecular weights (Mw) of 2.47−1.36E+05 had chain number-average degrees of polymerization (DPn) of 500−1000, 0−1 branch points per 1000 glucose units, higher setbacks, and high final viscosities and resulted in firmer gels than their lower Mw counterparts. Cohesiveness was inversely proportional to crystallinity, while stringiness increased with increasing DPn. Amylopectin fractions of low Mw (7.89−7.08E+07) with high branching ratios (>1.5), short branch chains (weight-average degree of polymerization, 15−18), and crystallinity >28% had high peak temperatures and low peak viscosity and shear thinned less. When cooled, these amylopectins formed weak gels, but during storage, the gels firmed and retrograded more than did their high Mw counterparts. Keywords: Corn; amylose; amylopectin; pasting; textural profile analysis; differential scanning calorimetry; DSC; molecular weight; retrogradation; crystallinity

Firming of starch gels and amylopectin retrogradation as related to dextrin production by α -amylase

The effect of dextrins produced by α-amylase on the firming and amylopectin retrogradation of wheat starch gels was studied. Different gel samples were prepared and included several ingredients, for example, α-amylase, vital gluten and glucoamylase. Amylopectin retrogradation, gel firming and the dextrin profile were analysed throughout a 5-day storage period. Both processes, i.e. firming and starch retrogradation, increased with time, and were not affected by the incorporation of gluten into the mixture. The well-known effect of α-amylase to retard bread crumb firming was also found to be relevant to starch gels. From the results obtained in this work, it seems that this anti-firming effect is not due to modifications of the starch but to dextrins produced by starch hydrolysis, since the effect did not occur when dextrins were removed by glucoamylase.

Effect of Dry Heat and Mild Alkaline Treatment on Functional Properties of Egg White Proteins

Physicochemical properties exhibited by the dried egg white protein molecule during the dry heat treatment at low water activity were assessed. Gelling properties of dried egg white proteins were greatly improved by heating in the dry state at a mild alkaline pH (under 9.50). The surface hydrophobicity increased with heating time, and sulfhydryl−disulfide exchange was accelerated at a mild alkaline dry heating. The proteins were deamidated by this treatment with no effect on solubility and hydrolysis. After 15 days of storage of the proteins in the dry state, the deamidation rate reached 12.2%. However, dry heating at higher pH (>9.50) caused detrimental effect on egg white proteins, resulting in the formation of insoluble aggregates by polymerization. Increasing solubility due to the deamidation of the denatured proteins and the reaction can be an important factor for forming excellent firm gels of dried egg white proteins. Thus, the combination of dry heating and deamidation under controlled pH values offers a new approach to improve the functional properties of food proteins and to study the structure−function relationship. Keywords: Egg white; gelation; elasticity; dry heating; pH; deamidation; alkali treatment

Coagulation of milk enriched with ultrafiltered or diafiltered microfiltered milk retentate powders

Abstract Rennet coagulation of milk with a total protein content of 3.5% (control) was compared to milk enriched to 4, 4.5 or 5% total proteins with a regular ultrafiltered milk retentate (RUF) powder obtained by spray drying, a diafiltered microfiltered milk retentate (DMF) powder and an acidified diafiltered microfiltered milk retentate (ADMF) powder obtained by freeze-drying. The protein to fat ratio for each milk was adjusted to 0.95. Evolution of milk coagulation was followed by a turbidity method. The coagulation parameters measured were: the lag time (Tlag), the time at inflexion point (Tmax), the rate of increase (Dmax), the optical density ratio at infinite time (OD∞), and the gel firmness (GF). The effect of adding CaCl2 (0.00, 0.01 or 0.02%) was also investigated. In all cases, enriched milk had different coagulation properties than control milk. The GF and coagulation parameters increased as the protein concentration in milk increased. The use of DMF powder to enrich milk modified the coagulation parameters more than the use of RUF powder. However, this effect was reduced by using ADMF powder, which contained less mineral than DMF powder. The time parameters, Tlag and Tmax, for DMF milk were shorter than those measured for control, RUF and ADMF milk. In addition, Dmax, OD∞ and GF for DMF milk were higher than those determined for control, RUF and ADMF milk. Differences observed between coagulation parameters of individual enriched milk types were reduced by addition of CaCl2.

Physicochemical and Structural Properties of Ultrafiltered Buffalo Milk and Milk Powder

Buffalo skim milk containing 10.20% total solids (TS), 3.96% protein, and 5.22% lactose was ultrafiltered at 50°C to 23.50% TS and 16.44% protein. Contents of TS, fat, ash, and protein increased during UF, and lactose content decreased. The composition of permeate was influenced by the concentration factor during UF of milk; as the concentration factor increased, TS, protein, ash, and lactose content increased. The rejection coefficients after 77% weight reduction were 52.52% for TS, 94.95% for protein, 100% for fat, and 52.04% for ash. Rennet coagulation time decreased, and gel firmness increased after coagulation as the protein concentration of the milk increased. As examined by scanning electron microscopy, particles of buffalo skim milk powder had smooth surfaces, but most had dents of varying sizes. Particle sizes ranged from 2 to 55 μm in diameter.

Enzyme-induced gelation of whey proteins: Effect of protein denaturation

The enzyme-induced gelation properties of unheated and denatured whey proteins (WP) were investigated. Solutions (9%, w v ) of whey protein isolate (WPI) were denatured by heating at 80 °C for 2–30 min, and gelation was induced by incubation with a Bacillus licheniformis protease (40 °C, pH 7.0). The gelation characteristics, as well as gel strength and microstructure, were examined. The heat treatments resulted in irreversible denaturation of up to 98% of the WP. Bacillus licheniformis protease (BLP) was able to induce gelation of both unheated and pre-heated WP, but the gelation process was strongly dependent on the extent of denaturation (%D). Higher %D resulted in earlier gelation and a faster increase in gel firmness. The relation between %D and the rate of gel firming was almost linear. The strength of the enzyme-induced gels increased continuously during 30 h of incubation. After 9 h, the gel with 98%D was 3.2 times stronger than that with 47%D, and 18 times stronger than the gel from unheated WPI (≈8%D). The latter gel had a particulate microstructure, whereas the gel from the highly denatured WPI (98%D) had a fine-stranded structure. This enzyme-induced gelation of partly denatured WP may be of interest for food applications.

The Chemical Basis of Molecular Weight Differences in Gelatins

The breakdown of intact collagen from bone or hide to produce commercial gelatin results in a poll/disperse product with respect to molecular weight. The mechanism of this breakdown and the role of the individual collagen chains in gel formation is not clearly understood.Analysis of these polypeptide chains for molecular iveight and inter-chain cross-linking of both commercial gelatin and isolated intact components from purified collagen, and the ability of both to form gels, should provide data on the mode of breakdown and the mechanism of gel formation. We have shown that the isolated pure α and β-components form firm gels, in which a high proportion of triple helix Is generated. In contrast, the α2 chain forms weak gels and generates little helix. The highly cross-linked high molecular weight components also produce weak gels, yet generate a high proportion of triple helix. It is possible that the rapid production of triple helices by chains in register due to cross-linking actually reduces network formation, in which multiple chain interactions forming short helices is preferable.

Comparative Properties of Bluefish (Pomatomus saltatrix) Gels Formulated by High Hydrostatic Pressure and Heat

High pressure was applied at levels of 300 to 3,742 atm for 30 min to formulate gels from bluefish meat paste, and the properties of the resulting gels were compared with those of heat-induced gels formulated at 90°C for 20 min, or at 60°C for 60 min. The moisture content of the pressure-induced gels was similar to that of the heat-induced gels, while protein contents and pH values of pressurized gels were slightly lower than those formulated by heat. Gels formed by pressure were more translucent as compared with those formulated by heat. Texture measurement indicated that there were no significant differences between the elasticities of the gels obtained under various pressures, although gel firmness increased with pressure. Overall, the heat-induced gels formulated at 90°C for 20 min were firmer but had similar elasticities to pressure-induced gels, while gels formulated at 60°C for 60 min were comparatively softer and had lower elasticities. The salt-extractable protein and protein digestibility studie...

‘Sugary-2’ starch for firmer gels: Friedman, R., Hauber, R. and Katz, F. (American Maize Technology, Inc., Dimmitt, TX, USA) United States Patent US 5 476 674

‘Sugary-2’ starch for firmer gels: Friedman, R., Hauber, R. and Katz, F. (American Maize Technology, Inc., Dimmitt, TX, USA) United States Patent US 5 476 674

Aseptic Rennet Coagulation of Ultra-High Temperature Processed Milk Concentrates

Milk was concentrated by pressure-driven filtration (UF or reverse osmosis) to 9.5, 15, 18, or 20% TS and then sterilized by UHT processing to 140°C for 4s using plate heat exchangers. Following sterilization, samples were aseptically inoculated with rennet to coagulate the milk, which was then stored at room temperature (22°C). We investigated the influence of TS, milk fat, extent of heat treatment, rennet dosage, storage temperature, and storage time on gel strength and syneresis as indicators of suitability for manufacturing a shelf-stable dairy dessert.As the TS content of the UF milk concentrate increased, gel strength also increased, and the optimum was obtained when milk was concentrated by UF to 18% TS. A small amount of added fat increased gel strength, but an increase in fat content from 1.5 to 3.5% decreased gel strength. Gel strength and syneresis increased as the rennet dosage was increased, and the optimum was in the range of 0.005 to 0.035 RU (rennet units)/ml of milk concentrate. Storage of the renneted UHT concentrates at 21°C yielded firmer gels and more syneresis than did storage at 4°C. Products stored for longer periods were also firmer, although syneresis increased during storage. Increasing the extent of whey protein denaturation by heating the concentrates to 81°C for 30min before UHT processing helped reduce syneresis of the gel during storage.

Evaluation of pure bacterial culture from fermented cassava as soy-yoghurt starter: a research note

Yoghurt-like products were prepared by incubating sterile soymilk with 5% exudate of cassava root pulp previously fermented for 24–48 h at 42 °C. The products had pH values not less than 4.4, were characterized as firm gels without signs of breakage and emitted yoghurt-type aroma after incubation at 42 °C for 6 h. The exudate from a 12 h fermented pulp did not produce yoghurt-like properties. A 2% pure culture inoculum of Gram-positive bacilli that was originally isolated from one of the yoghurt-like products produced pH values of 5.4, 5.0, 3.9 and 3.3 in soymilk fortified with 1% sucrose enriched with 0 (control), 1, 4 and 8% partially lysed dry yeast, respectively. Incubation of the soymilk-yeast samples was for 7 h at 42 °C. Culture activity (pH decrease per hour) was highest in the first hour of incubation, attained a steady state in the intermediate stages and decreased in the last 2 h at all levels of added yeast. Linear regression of pH decrease on duration of incubation showed an overall two-fold increase in activity of culture stimulated with 4 and 8% yeast relative to that stimulated with 0 and 1 %. Correlation coefficient between the same variables decreased from −0.99 for the control to −0.91 for soymilk that contained 8% yeast. Addition of lactose-containing dairy ingredients to soymilk-base for yoghurt-making to give accelerated acid production is not necessary if non-dairy-based culture is utilized.

Gelation properties of deamidated soluble wheat proteins

Compared with native wheat gluten proteins, chemically modified deamidated gluten proteins are more readily dispersed in aqueous solution. In this paper the gelation behaviour of commercial deamidated gluten, commonly referred to as soluble wheat protein (SWP) on heating as well as its interaction with calcium and basic proteins was investigated. Soluble wheat protein decreased in viscosity on heating at 60°C due to the breakdown of protein aggregates which was observed by phase contrast microscopy. Heating to 60°C was accompanied by an increase in hydrophobicity without conformational transitions as observed by differential scanning calorimetry. In aqueous solutions at concentrations greater than 17% wlw and after autoclaving at 120°C, SWP produced firm gels which were examined by large deformation testing. In the presence of calcium strong but coarse gels were formed which exhibited syneresis. The addition of 0.1–0.5% wlw of basic lysozyme or clupeine to the highly negatively charged SWP induced gelation at the lower temperature of 80°C which was detected by small deformation rheological testing and microscopy using basic and acidic stains. The structure and mechanism of lysozyme-induced gelation of SWP is different from the high thermal (>100°C) gelation of SWP alone. In the lysozyme-induced gelation non-covalent mainly electrostatic interactions occur between the positively charged lysozyme and the negatively charged soluble wheat proteins with the absence of conformational changes in the SWP. In contrast, in the heat gelation of SWP proteins at 120°C it is proposed that the intra-disulphide bonds are broken leading to conformational changes and subsequent association and gelation. This mechanism is supported by the fact that gelation occurred spontaneously in the presence of urea and β-mercaptoethanol indicating that in SWP the disulphide bonds normally prevent gelation unless exposed to very high heat (120°C) or disulphide reducing reagents.