Gel Firmness Research Articles

Isolation, structural features and rheological properties of water‐extractable β‐glucans from different Greek barley cultivars

Abstractβ‐Glucans were isolated from six Greek barley cultivars (Persefoni, Kos, Thessaloniki, Athinaida, Dimitra and Triptolemos) by water extraction at 47 °C, enzymatic removal of starch and protein and subsequent precipitation of the water‐soluble β‐glucans with 37% (w/v) ammonium sulfate saturation. The purity of barley β‐glucans was high (>93% dry basis) with some small contamination by protein (<3.84%). The molecular size of the β‐glucan isolates was determined by high‐performance size‐exclusion chromatography (HPSEC); the weight‐average molecular weights and the intrinsic viscosities ranged between 0.45 × 106 and 1.32 × 106 and 2.77 and 4.11 dl g−1, respectively. Structural features of barley β‐glucans were revealed by 13C NMR spectroscopy and high‐performance anion‐exchange chromatography (HPAEC) of the oligomers released by the hydrolytic action of lichenase. Lichenase degradation showed that β‐glucans from all barley cultivars consisted of blocks of cellotriosyl and cellotetraosyl units, accounting for 90.6–92.3% of the total oligomers released, with a molar proportion of these units between 2.31 and 2.77. Rheological measurements of aqueous solutions/dispersions of β‐glucans showed the behaviour of non‐interacting polysaccharides and a transition from the typical viscoelastic response to gel‐like properties after a time period that depended on the molecular size of the polysaccharide. The lowest molecular size β‐glucans from the Triptolemos cultivar showed shorter gelation times than their higher molecular weight counterparts. The effect of sugar incorporation (glucose, fructose, sucrose, xylose and ribose), at a concentration of 30% (w/v), to the β‐glucans gels (6% w/v) on compression parameters seemed to be related to the type of sugar used; the pentose sugars substantially reduced gel firming. Copyright © 2004 Society of Chemical Industry

Functional Properties of Improved Glycinin and β-nglycinin Fractions

ABSTRACT: Glycinin and β-conglycinin have unique functionality characteristics that contribute important properties in soy foods and soy ingredients. Limited functionality data have been published for glycinin and β-conglycinin fractions produced in pilot-scale quantities. Protein extraction conditions were previously optimized for our pilotscale fractionation process to maximize protein solubilization and subsequent product recovery. Glycinin, β-conglycinin, and intermediate (mixture of glycinin and β-conglycinin) fractions were prepared using optimized-process (OP) extraction conditions (10:1 water-to-flake ratio, 45°C) and previous conditions termed Wu process (WP) (15:1, 20°C). Viscosity, solubility, gelling, foaming, emulsification capacity, and emulsification activity and stability of the fractionated proteins, and soy protein isolate (SPI) produced from the same defatted soy white flakes were compared to evaluate functional properties of these different protein fractions. Differential scanning calorimetry, sodium dodecylsulfate-polyacrylamide gel electrophoresis, and surface hydrophobicity data were used to interpret functionality differences. OP β-conglycinin had more glycinin contamination than did the WP β-conglycinin. OP and WP solubility profiles were each similar for respective glycinin and β-conglycinin fractions. Emulsification activities and stabilities were higher for OP β-conglycinin and OP intermediate fractions compared with respective WP fractions. β-Conglycinin and SPI emulsification capacities (ECs) mirrored solubility profile, whereas glycinin ECs did not. OP glycinin had a higher foaming capacity than WP glycinin. OP and WP intermediate fraction apparent viscosities trended higher than those of other protein fractions. β-Conglycinin dispersions at pH 3 and 7 produced firm gels at 80°C, whereas glycinin dispersions formed weaker gels at 99°C and did not gel at 80°C.

Improvement of rheological properties of firm acid gels by skim milk heating is conserved after stirring

The enhancement of the strength of set acid gels by heating milk was related to rheological parameters (water retention capacity, storage modulus) of corresponding stirred gels. To obtain accurate rheological data from stirred gel it was necessary to maintain a constant granulometry of gel particles and to recognize time after stirring as a contributing factor. Two hours after stirring, the gel exhibited a higher storage modulus when milk was heated above 80 degrees C. A measurement of viscosity of just-stirred yoghurt was sufficient to predict correctly the quality of a stirred gel analysed by viscoelastic measurements. Increased resistance to syneresis of just-stirred gels was related to higher viscosity. The quantity of beta-lactoglobulin (beta-Ig) bound to casein micelles explains the improvement of these gel qualities. We have considered that the structure of the initial firm gel (mesostructure level) was conserved in fragments within the stirred gel. Consequently, the explanation given by various authors for the effect of heating milk on the properties of set gels can also be applied to stirred gels. The same mechanism, described in literature for structure formation of set gels from acidified milk is purposed to explain the role of heating milk on the recovery of gel structure after stirring. The beta-Ig association with casein micelles during heating favoured micelle connections during the acidification. It also favoured the association of gel fragments after stirring during the recovery in gel structure.

Characteristics of Low‐fat Beef Patties Formulated with Carbohydrate‐Lipid Composites

ABSTRACT: Chemical, physical, and sensory characteristics of low‐fat beef patties containing carbohydrate‐lipid composites (CLCs) were compared with those of all‐beef patties. The CLC gels contained high‐amylose cornstarch, maltodextrins, and canola oil. CLC patties had higher moisture, cooking yield, and fat retention than 20%‐fat control patties. CLCs improved tenderness and juiciness and decreased cohesiveness of low‐fat beef patties compared with 10%‐fat control patties. Despite differences in CLC gel firmness, patties made with CLC gels containing corn, potato, and tapioca maltodextrins had similar physical and sensory properties. These results suggest that CLC gels perform well as a partial fat replacer in beef patties while providing flexibility in gel firmness selection.

Firmness of pressure-induced casein and whey protein gels modulated by holding time and rate of pressure release

The main protein fractions of milk, casein and whey protein, may react differently to processing due to their amino acid sequence and conformation and their ability to build up intermolecular covalent and non-covalent bonds. Gels made from solutions of micellar casein and whey protein isolate were induced by applying ultra-high pressure (600 MPa/30 °C). The pressure built up was held constant at 200 MPa min −1, while the holding time of 0.15 and 30 min was varied as well as the pressure release rate (20, 200, 600 MPa min −1). The firmness of the pressure-induced whey protein gel was essentially influenced by the degree of whey protein denaturation and determined by the amount of disulfide bonds stabilizing the gel microstructure. In contrast, the firmness of pressure-induced casein-based gels was mainly influenced by pressure release rate. A slow pressure release produced a rough and weak gel. A high release rate, however, caused a homogeneous microstructure to be formed that created a high level of firmness.

Starch Granule Size Strongly Determines Starch Noodle Processing and Noodle Quality

ABSTRACTChemical compositions, physical properties, and suitability for starch noodle making of different granule size fractions from potato and sweet potato starches were studied. The ash content, amylose content, phosphorus content, gel firmness, and freeze‐thaw stability of small‐size granule fractions(< 20 μm) were significantly different from those of the large‐size granule fractions. The processibility and the qualities evaluated by objective and subjective methods of both dried and cooked starch noodles made from small‐size granule fractions were significantly better than those made from their initial starch preparations and much better than those made from the large‐size granule fractions.

Effects of pork collagen on thermal and viscoelastic properties of purified porcine myofibrillar protein gels

The objectives of this study were to examine the thermal, water-binding and viscoelastic properties of mixed protein systems containing purified myofibrils from porcine semimembranosus (MP) and pork collagen (PC) during gelation and subsequent cooling. MP:PC mixtures (100:0, 90:10, 80:20, 70:30, 60:40, 50:50) normalized to 4% protein were evaluated. No significant differences in thermal characteristics of these mixtures could be detected using differential scanning calorimetry. A primary peak was observed near 66 °C. Using small-strain oscillatory testing, the rheological properties during gelling and cooling were quantified. Storage modulus ( G′) increased upon heating for all treatments, but the rate of gel firming and the G′ value at 85 °C were significantly lower ( P<0.05) as PC was added to the mixed protein system. Upon cooling, gels revealed a significantly lower ( P<0.05) rate of gel firming and significantly lower ( P<0.05) G′ value at 5 °C in samples with 20% inclusion of PC and higher. Addition of PC yielded a significant linear ( R 2=0.65; P<0.01) increase in the water-holding capacity (WHC) of the gels, indicating that the matrix formed in MP:PC gels had a greater ability to entrap water than that of the control MP gels. The inclusion of 10% PC resulted in gels with significantly higher ( P<0.05) WHC and similar firmness when compared with gels comprised of MP as the only protein source.

Heat induced gelation of acid milk: balance between weak and covalent bonds.

Gelation of acidified milk at pH[ges ]5, after heat treatments is a well known phenomenon, due to the precipitation of whey proteins, and especially β-lactoglobulin onto κ-casein (Sawyer, 1969). High heat treatments cause denaturation of whey proteins which associate with κ-casein through disulphide interchange reactions (Hill, 1989). Since their charge is reduced, the denatured proteins associated with casein micelles become susceptible to aggregation when milk is then acidified, which promotes enhanced protein–protein interactions (Lucey et al. 1997). The gelation phenomenon involves disulphide bonds (Hashizume &amp; Sato, 1988; Goddard, 1996) which are responsible for the gel firmness (Goddard, 1996). However, other interactions between proteins can occur, such as hydrogen and hydrophobic bonds, especially at the initial stage of interactions (Haque et al. 1987; Haque &amp; Kinsella, 1988; Jang &amp; Swaisgood, 1990). It is therefore relevant to investigate a possible contribution of weak linkages to the gel structure and firmness.

Effect of Oil Content and pH on the Physicochemical Properties of Corn Starch‐Soybean Oil Composites

ABSTRACTStarch‐lipid composites are a new category of fat replacers. The physicochemical properties of reconstituted corn starch and soybean oil composites (CSSBOC) were evaluated and compared with the properties of reconstituted jet‐cooked corn starch (JCCS). Gel firmness, thermal properties, and hot pasting properties at two pH levels and two oil content levels were studied. Amylose content of CSSBOC was unaffected by processing. Buffer pH significantly affected the firmness of the gels made with JCCS. Gels appeared to have a more ordered structure and were firmer at pH 3.4 than at pH 6.0. The firmness of gels made with CSSBOC was not affected by pH or oil content. Retrogradation enthalpy of the gels made with JCCS was significantly affected by pH. Differences in the thermal characteristics of gels made with CSSBOC were attributed to pH and oil content. Peak viscosity, cold paste viscosity, and breakdown viscosity changed significantly when CSSBOC pastes were reconstituted in different pH buffers. Only hot paste viscosity and cold paste viscosity changed significantly when JCCS pastes were reconstituted in different pH buffers. Results establish critical parameters for processing decisions and for the understanding of the behavior of CSSBOC in food system models in which pH is an important factor.

Development of a fermented goat's milk containing probiotic bacteria

Abstract A set-type fermented milk manufactured from goat's milk was developed. Optimal curd tension was achieved by supplementation of milk with skim milk powder and whey protein concentrate (WPC). Milk was fermented employing a commercial probiotic starter culture (ABT-2), which contained Streptococcus thermophilus ST-20Y, Lactobacillus acidophilus LA-5, and Bifidobacterium BB-12. Supplementation of milk with 3% WPC reduced fermentation time by 2 h due to the increase in viable counts of S. thermophilus and Bifidobacterium by 0.3 and 0.7 log units, respectively. Addition of WPC increased the protein content (1%) as well as potassium and magnesium content (0.3 and 0.02 g kg −1 , respectively). Increase of the protein content led to an increase in the apparent viscosity and gel firmness of the product, and at the same time whey syneresis was reduced. As a consequence, the product received a high score for appearance, taste, aroma, texture and overall acceptance.

Rheological Characterization of Synergistic Mixtures of Carrageenan and Locust Bean Gum for Aqueous Gelcasting of Alumina

Previous works have shown that carrageenan can be successfully used in the aqueous gelforming of powders, because carrageenan forms a firm gel, similar to that formed by agarose, but at a much lower cost. In this work, the synergistic effect of carrageenan with locust bean gum is studied. The rheological behavior of 2 wt% solutions of these polysaccharides and their mixtures are measured under mixing conditions (60°C) and by recording the viscosity and elastic modulus on cooling. The effect of the addition of these solutions to 50 vol% alumina slurries up to a concentration of 0.5 wt% is studied. Although gelling time increases, the resulting gels are stronger than for carrageenan alone. Gelcast alumina bodies with green and sintered densities of 57% and 97.6% of theoretical have been obtained.

Thermosetting gels with modulated gelation temperature for ophthalmic use: the rheological and gamma scintigraphic studies.

For ophthalmic drug delivery, Pluronic F127 solutions have a phase transition temperature too low for them to be instilled into the eye at room temperature. Refrigerator storage is usually required to make administration easier, whereas the potential irritation of cold to the sensitive ocular tissues may result in poor topical bioavailability. The purpose of this study is to develop a thermosetting gel with a suitable phase transition temperature by combining Pluronic analogs and to examine the influence of incorporating mucoadhesive polysaccharide, sodium hyaluronate (HA-Na), on the ocular retention of the gel. Dynamic rheological method and single photon emission computing tomography (SPECT) technique were used to ex/in vivo evaluate the thermosetting gels, respectively. An optimized formulation containing 21% F127 and 10% F68 increased the phase transition temperature by 9 degrees C as evaluated by elasticity modulus compared to that of individual 21% F127 solution. Rheological behaviors of the Pluronic solutions showed that the combined Pluronic formulation was free flowing liquid below 25 degrees C and converted to a firm gel under the physiological condition. Furthermore, this formulation possessed the highest viscosity both before and after tear dilution at 35 degrees C. Gamma scintigraphic data demonstrated that the clearance of the thermosetting gel labeled with 99mTc-DTPA was significantly delayed with respect to the phosphate buffered solution, and at least a threefold increase of the corneal residence time was achieved. However, no further improvement in the ocular retention was observed when adding HA-Na into the thermosetting gel due to the substantially decreased gel strength.

Rheological Characterization, Crystallization, and Gelation Behavior of Monoglyceride Gels

Saturated monoglycerides can form firm gels in water. These gels are networks of stiff plate-like β-crystals of monoglycerides (a “cardhouse”), grown from a space-filling lamellar liquid-crystalline phase. The molecular mechanism of crystallization is discussed in the light of network formation. The concentration dependence of gel development of (shear-cooled) monoglyceride gels has been studied by rheology. A gelation mechanism has been proposed, consisting of two steps: (i) After formation of a nucleus, rapid crystallization in a lateral direction occurs (probably within one bilayer) by which the first space-filling network is formed. (ii) This is followed by reinforcement of the network by which stacks of crystalline bilayers are formed. The plate-like crystals are linked in connective domains or junction zones, probably containing all the material (cosurfactants, diglycerides, etc.) that does not fit in the crystalline array. Small deformation rheology shows that above about 2 wt% monoglyceride a percolating network is formed. The large deformation rheology is typical for a particle gel with a relatively small strain at failure (both in shear deformation and compression). The connective domains or junction zones already fail when relatively small deformations are put on the system.

Properties of gels from whey protein concentrate and honey at different pHs

Structural and functional properties of heat-induced gels from whey protein concentrate (WPC)-honey prepared at pHs 3.75, 4.2 and 7.0 were analyzed. Gel structure was observed by scanning electron microscopy, and the apparent transition temperature for protein denaturation was determined by differential scanning calorimetry. The solubility of the protein components in different extraction media, and the water-holding capacity, firmness, elasticity, relaxation time, adhesivity, cohesiveness and color of gels were determined. Results show that disulfide interchange reactions are important in determining the elasticity, water-holding capacity, relaxation time and cohesiveness of WPC gels. Honey decreases the relaxation time of gels prepared at pHs 7.0 and 4.2, and increases the browning and the water-holding capacity of gels, the apparent transition temperature of WPC dispersions at the three pHs assayed, and the adhesivity of acidic gels. The solubility of the protein constituents of gels in a pH 8.0 buffer increases slightly at honey concentrations of 27.5% or more, which correlates with a decrease in the gel cohesiveness, having these gels a structure with smaller pores. The products obtained could be utilized in the formulation of different desserts, such as flans and cake and tart fillings.

Viscoelasticity of oxidized starch/low methoxy pectin mixtures in the presence of glucose syrup

The structural properties of mixtures of pectin, oxidized starch and glucose syrup were investigated using small deformation dynamic oscillation. In the absence of added calcium, preparations of low methoxy pectin with glucose syrup formed viscous solutions, which remained crystal‐free at subzero temperatures. Samples of oxidized starch and glucose syrup, on the other hand, exhibited solid‐like behaviour because of the crystalline nature of the amylose‐like helices. Mixtures of the two polysaccharides with the co‐solute clearly showed phase inversion from liquid to solid‐like behaviour with increasing amounts of starch in the formulation. The transformation was reflected in the textural properties of samples, which varied from thick solutions to firm gels. The viscoelasticity of the system was modified further by the introduction of high methoxy pectin. Preparations of high methoxy pectin and glucose syrup formed rubbery gels whose amorphous nature underwent a glass transition during cooling.

Textural and Physical Properties of Acid–Induced and Potassium–Substituted Low–Sodium Surimi Gels

ABSTRACT: Textural and physical properties of acetic acid‐induced and salt‐induced surimi gels were evaluated. The addition of 2 to 3% acetic acid significantly decreased the shrinkage and total expressible fluid and increased firmness compared to 0.5% acetic acid added. Acid‐induced gels without starch were significantly firmer than those with starch and salts. There was no peak in storage modulus with the addition of acid in the temperature range of 32 to 43 °C, suggesting that the acid‐induced gelation did not require setting as the salt‐induced one. Partial substitution (1%) of KCl for NaCl did not change the storage modulus of the sol during heating and gel firmness. However, KCl and NaCl weakened the firmness of the acid‐induced gel.

Effect of type and level of supplement on performance of dairy cows grazing on alpine pasture

An experiment was carried out on 32 dairy cows (average yield 21.9 ± 2.7 kg/d) grazing on summer alpine pasture, in order to examine the effect of two types of supplement - Starchy (42% of cereal) and Fibrous (41% of beet pulp) - both provided at two different levels - Low (1 kg of supplement per 5.0 kg of energy corrected milk (ECM)) and High (1 kg of supplement per 3.3 kg of ECM) - on herbage intake, milk yield and quality. The supplement was distributed twice a day, during milking, at a constant level throughout the experiment (July and August), as calculated according to the daily milk yield in a one-week preliminary period. Meteorological measurements, herbage quality and availability, herbage intake, animal body condition score (BCS), milk yield, chemical and rheological traits were determined. The herbage intake was higher (11.9 kg organic matter (OM)/d) with the Fibrous supplement at Low level. Even if the supplementation covered up to one third of the total intake of OM, none of the experimental groups increased BCS, and the Starchy-Low group showed a decrease in BCS significantly different from zero. The increase in the level of supplementation (from 3.5 to 5.0 kg OM/d in Low and High groups, respectively) improved the ECM yield by an average of 1.2 kg/d (P<0.05), without significant changes in the chemical composition of the milk, while the supplement type had no significant effects on either milk yield or composition. The mean coagulation properties were better with the Fibrous supplement as compared to the Starchy one – rennet clotting time (r): 16’24’’ vs 19’15’’ (P<0.05), time for aggregation (K20): 5’03’’ vs 6’45’’ (n.s.), gel firmness (a30): 26.1 mm vs 20.8 mm (P<0.05) - without significant differences derived from the level of supplementation.

Gelling agents, silver nitrate and sequestrene iron influence adventitious shoot and callus formation from Rubus leaves

Blackberry (Rubus spp.) cultivars Chester Thornless, Kotata, Marion, and Navaho were evaluated for morphogenic potential using the top one to four leaves from in vitro-grown shoots. In each experiment adventitious shoots were regenerated via organogenesis without an intervening callus phase. Rooting was spontaneous when shoots were transferred to a medium without growth regulators or with indole-3-butyric acid (IBA). Three gelling treatments (agar, Gelrite, and a combination) calibrated for equal gel firmness [110 g/(1.1 cm)2 π] did not affect explant regeneration or the number of shoots per explant, but did affect callus production. Significantly more callus (P≤0.05) was induced on regeneration medium (RM) with 10 μM N6-benzyladenine (BA), 0.5 μM IBA, and 0.19% Gelrite, than on medium containing either 0.71% agar, or the 0.35% agar/0.11% Gelrite combination. Explants on RM with 5 μM IBA produced significantly more callus, but fewer shoots, compared to zero or 0.5 μM IBA treatments for all gel treatments. Adding 200 mg l−1 sequestrene iron [sodium ferric ethylene diamine di-(O-hydroxyphenylacetate)] at the first transfer onto RM induced more shoots per explant than the control, but did not influence the amount of callus produced. Sequestrene iron in the second transfer on RM significantly increased the regeneration (caulogenesis) frequency from 30 to 40% for ‘Marion’ and from 23 to 43% for ‘Kotata’. Silver nitrate significantly reduced callus production for all treatments, but did not affect the frequency of caulogenesis or the number of shoots per explant.

Rheological properties of milk gels made with coagulants of plant origin and chymosin

The rheological properties of milk gels made using coagulants obtained from the plants Cynara cardunculus L. and Cynara humilis L. were compared with those of fermentation-produced chymosin, using dynamic low amplitude oscillation as well as large strain (yield) testing. Gelation experiments were performed at 321C using skim milk powder that had been reconstituted for 2 or 16 h at 321C. The storage modulus (G 0 ), loss tangent (tand) at low frequency (0.002 Hz) andyieldstress were higher for chymosin-induced gels than those of plant coagulants, when tested B6 h after coagulant addition. Plant coagulants were slightly more proteolytic than chymosin, andcasein hydrolysis may have resultedin lower gel firmness. Most of the rheological properties were similar for the two plant coagulants, in agreement with their similar enzyme contents. Gelation properties were different in milk reconstituted for 2 or 16 h. This behaviour was probably due to casein hydrolysis by plasmin, as milk reconstituted for 16 h at 321C hadsignificant levels of degradation of both as- and b-caseins. The addition of soybean trypsin inhibitor which inhibits plasmin activity resulted in similar gelation profiles for gels made from milk reconstituted for 16 and 2 h. r 2002 Publishedby Elsevier Science Ltd .

Gelling behaviour of polyose from tamarind kernel polysaccharide

Polyose was isolated from tamarind kernel powder (TKP) in 50% yield by alcohol extraction of an acidified boiled aqueous extract, which was subsequently dried and pulverised. The gelling behaviour of polyose vis-à-vis pectin, and its blends with pectin was studied in a 65°Brix sucrose solute as a function of pH and concentration. One percent pectin gave a good firm gel, while 80:20 and 60:40 blends of pectin/polyose gave a firm gel at 1.5 and 2.0%, respectively. A 40:60, 20:80 and 0:100 blend of pectin/polyose gave a good set at 2.0%, beyond which the jellies were hard and difficult to chew. From the values of gel strength, 2% polyose from TKP was found to adequately substitute 1% pectin in ready-to-eat jelly formulations.