Influence of selected hydrocolloids on triticale starch rheological properties

The aim of the study was to define the influence of selected nonstarch polysaccharides (guar gum, xanthan gum and arabic gum) on several rheological properties of triticale starch pastes/gels, at constant polysaccharide concentration (6.5 g/100 g). These included pasting characteristics, flow curves at 50 °C and mechanical spectra at 25 °C. It was found that the presence of a gum in a system modified the rheological properties of triticale starch gels/pastes, depending on the type and concentration of the gums. In the case of guar and xanthan gums, higher pasting viscosity was observed and the shear stress was increased compared with native starch. The presence of guar gum reduced the degree of thixotropy hysteresis, negative values for this being found for systems with xanthan in spite of their shear‐thinning behaviour. Systems containing arabic gum displayed lower values of pasting and flow viscosity. The type and concentration of gums added to the polysaccharide influenced the viscoelastic properties of the gels.     

Influence of pH and added gums on the properties of konjac flour gels

The gel strength and texture of konjac gel and mixed gels of konjac and various gums were measured after gelation at various concentrations of alkali. A selection of different alkaline reagents was used. Regardless of alkali concentration, increasing konjac levels caused a decrease in pH but an increase in hardness and strength of konjac/gellan gum mixed gels. The highest gel strength and hardness were given by mixed konjac/gellan gum gels using sodium carbonate as the gelling medium. Under similar gelling conditions, the addition of gellan gum resulted in the greatest gel hardness. Of the gums examined, a possible synergistic effect on konjac/gellan gum mixed gel texture was observed.     

Insolubilized Whey Protein Concentrate and/or Chicken Salt-Soluble Protein Gel Properties

Properties of gels prepared from five whey protein concentrates (WPC) with protein solubilities ranging from 27.5% to 98.1% in 0.1M NaCl, pH 7.0, chicken breast salt-soluble protein (SSP), or a combination of SSP and WPC at pH 6.0, 7.0 or 8.0 were compared. WPC did not form gels when heated to 65°C. SSP gels heated to 65°C were harder than those heated to 90°C at all pHs and hardness decreased as pH was increased. Hardness of combination gels heated to 65°C increased as WPC solubility decreased at all pHs; however, the opposite trend was observed at 90°C. Combination gels of the same WPC solubility at 65°C were more deformable than those heated to 90°C.     

Modification of rheological properties of whey protein isolates by limited proteolysis

Whey protein isolate (WPI) was subjected to limited tryptic hydrolysis and the effect of the limited hydrolysis on the rheological properties of WPI was examined and compared with those of untreated WPI. At 10% concentration (w/v in 50 mM TES buffer, pH 7.0, containing 50 mM NaCl), both WPI and the enzyme-treated WPI (EWPI) formed heat-induced viscoelastic gels. However, EWPI formed weaker gels (lower storage modulus) than WPI gels. Moreover, a lower gelation point (77 °C) was obtained for EWPI as compared with that of WPI which gelled at 80 °C only after holding 1.4 min. Thermal analysis and aggregation studies indicated that limited proteolysis resulted in changes in the denaturation and aggregation properties. As a consequenece, EWPI formed particulated gels, while WPI formed fine-stranded gels. In keeping with the formation of a particulate gel, Texture Profile Analysis (TPA) of the heat-induced gels (at 80 °C for 30 min) revealed that EWPI gels possessed significantly higher (p < 0.05) cohesiveness, hardness, gumminess, and chewiness but did not fracture at 75% deformation. The results suggest that the domain peptides, especially β-lactoglobulin domains released by the limited proteolysis, were responsible for the altered gelation properties.     

Effect of polysaccharides with different ionic charge on the rheological,microstructural and textural properties of acid milk gels

The effects of addition of polysaccharides with different ionic charge on rheology, microstructure, texture and water holding capacity (WHC) of acid milk gels were studied and compared to that of gelatin addition. Similar to gelatin, starch (neutral) and xanthan gum (anionic) did not prevent milk gelation in the first 30 min of the acidification stage, even at high concentrations, and the typical casein network in acid milk gels could still be seen from electron micrographs; gelling and melting of these hydrocolloids were observed during the cooling and heating stages at specific concentrations. On the other hand, two neutral polysaccharides, guar gum (≥ 0.05%) and locust bean gum [LBG] (≥ 0.1%) inhibited milk gelation from the beginning of the acidification stage; the microstructure of the gel was modified greatly and no gelling/melting was observed during the cooling or heating stages. Another anionic polysaccharide, carrageenan, induced earlier milk gelation at low concentration (≤ 0.05%), but inhibited gelation entirely at high concentration (0.2%); inflections at ~ 27 °C and 21 °C were also observed during the cooling and heating stages at 0.05% concentration. The gel microstructure was not changed greatly, but showed smaller particle size at a carrageenan concentration of 0.05% than control sample. None of the polysaccharides showed as much improvement in WHC of the milk gels as gelatin did. Hence, xanthan and starch were found to be closer to gelatin in their effect on acid milk gels compared to guar gum, LBG and carrageenan.     

The effect of pH and calcium ion on rheological behaviour of β‐lactoglobulin‐basil seed gum mixed gels

Effect of pH (4.5–7.5) and Ca²⁺ (0.01–0.5 m ) on gelation of single and mixed systems of 10% β‐lactoglobulin (BLG) and 1% basil seed gum (BSG) was investigated. The gelling point of BLG and BSG gels was strongly pH‐dependent, and stiffer gels formed at higher pH. The BLG gels were formed upon heating to 90 °C and reinforced on cooling to 20 °C; however, the gelation of BSG occurred at temperatures below 70 °C. By increasing Ca²⁺ concentration, storage modulus of BLG and BSG gels were increased, although pH had a greater effect than Ca²⁺. In contrast, mixed systems showed two distinct types of behaviour: BLG gel formation and BSG network, suggesting that phase‐separated gels were formed. In addition, higher strength was obtained for BLG‐BSG mixture at higher Ca²⁺ concentration.     

Effect of temperature and pH on the properties of skim milk gels made from a tamarillo (Cyphomandra betacea) coagulant and rennet

Reconstituted skim milk was gelled with a crude protease extract from tamarillo [Cyphomandra betacea or Solanum betacea (syn.)] fruit and compared with gels prepared with calf rennet. The effects of temperature and pH on the gelation of skim milk were investigated by small deformation oscillatory rheology. The tamarillo extract-induced gels had a faster rate of increase in the elastic modulus (G′) at the early stage of gelation than rennet-induced milk gels. This was probably due to the broader proteolytic activity of tamarillo protease extracts as shown by sodium dodecyl sulfate–PAGE analysis. Confocal microscopy also showed that the milk gels resulting from the addition of tamarillo extracts had larger voids than rennet-induced milk gels. The proteolytic activity of tamarillo extracts was found to be optimal at pH 11. For both rennet and tamarillo extracts, the aggregation time was similar between pH 6.7 and 6.5, but the aggregation time of rennet-induced milk gels was lower than that of milk gels obtained by the addition of tamarillo extracts at pH lower than 6.5. An increase in temperature was found to have a significant effect on aggregation time, particularly at 20°C, where rennet did not coagulate milk in 3 h but the tamarillo extracts coagulated milk within 2 h. The results of this study suggest that extracts from tamarillo fruit could be used for milk gelation, particularly under lower temperature or high pH conditions.     

Ca2+-Induced Gelation of Pre-heated Whey Protein Isolate

Addition of CaCl₂ to pre-heated whey protein isolate (WPI) suspensions caused an increase in turbidity when pre-heating temperatures were ≥ 64°C. Pre-heating to ≥ 70°C was required for gelation. WPI suspensions which contained CaCl₂ became turbid at 45°C and formed thermally induced gels at 66°C. Thermally and Ca²⁺-induced gels showed significant time/temperature effects but the penetration force values in the Ca²⁺-induced gels were always lower. However, Ca²⁺-induced gels were higher in shear stress at fracture. The Ca²⁺-induced gels had a fine-stranded protein matrix that was more transparent than the thermally induced gels, which showed a particulate microstructure.     

On the temperature reversibility of the viscoelasticity of acid-induced sodium caseinate emulsion gels

Viscoelastic properties of acid-induced sodium caseinate emulsion gels have been investigated using a controlled shear stress rheometer. Gelation was introduced by addition of acidulant glucono-δ-lactone (GDL) at three different temperatures (5, 25 and 45°C). It was found that the gelation temperature has a significant effect on the rate of gelation and on the dynamic moduli of the emulsion gels. The rheology of these emulsion gels was investigated over the temperature range 5–45°C. The viscoelasticity of the emulsion gel prepared at 45°C was temperature reversible, suggesting that the temperature change only affects the strength of physical bonding within the network and not the gel microstructure. In contrast, the temperature-dependent viscoelasticity of the emulsion gel prepared at 5°C exhibited a highly irreversible character. This implies significant structural reorganization of the network during the heating stage from 5°C. Analogous temperature irreversibility has been observed in emulsion electrophoretic mobility measurements and in solution surface tension measurements of the corresponding caseinate systems at pH values near the isoelectric point of the protein.     

Storage Stability of Antioxidant-Washed Myofibrils From Chicken White and Red Muscle

Oxidation and gel-forming ability of chicken white (breast) and red (leg) muscle myofibrillar proteins during storage at 0°C were examined. Breast myofibril gels exhibited greater shear moduli than leg myofibril gels throughout 8 days storage. Shear moduli of both breast and leg gels in the intermediate temperature zone (45–55°C) decreased during storage, but at >55°C, they either increased or remained unchanged. Lipid oxidation was inhibited by washing myofibrils with antioxidants propyl gal-late, ascorbate, and tripolyphosphate. However, these antioxidants did not affect the content of protein carbonyls, and only slightly decreased the amine content during storage. Storage affected the kinetic process of myofibril gelation independently of antioxidant treatments.     

Influence of Gluten and Gum Additives and Cryogenic Treatment on Some Properties and Morphology of Wheat Starch Complex Gels

The influence of gums (guar and xanthan) and gluten additives on the physicochemical properties and structural features of wheat starch gels (8%, w/w) subjected to cryogenic treatment at various temperatures (−9°C, −20°C, −40°C) was studied. Shear modulus and breaking stress of the gels were measured, the gels' morphology was studied with optical microscopy and the local mobility of water in the gels was determined with ESR. The total concentration of polysaccharide additives did not exceed 1% (w/w), and a 65:35 (w/w) mixture of guar and xanthan gums proved to be the optimal additive, which caused a noticeable increase in rigidity and strength of the resulting complex gels. Shear modulus and breaking stress of the gels decreased with lowering the temperature of the cryogenic treatment. The heterogeneous morphology of thin sections of the gel samples was revealed via optical microscopy. ESR studies showed that the local mobility of water was much lower in the gels than in pure water.     

HEAT-INDUCED GELATION AND PROTEIN-PROTEIN INTERACTION OF ACTOMYOSIN1

Natural actomyosin (NAM) and “crude” actomyosin formed gels yielding maximum strengths (from back extrusion force) at pH 5.0 and 5.5, respectively. At pH 6.0, NAM gels had a least protein concentration endpoint (LCE) value of 6 mg/ml. Gel strength increased exponentially with an increase of NAM concentration from 3.75–10 mg/ml. With constant time (30 min)-temperature heating, NAM gel forces increased by 20.5% (NS, P>0.05) in the 30–80°C range. Arrhenius plots of NAM interaction in solution and in gelation at pH 6.0 indicated two different reaction mechanisms within the temperature zones above and below approximately 35°C for solutions and 40°C for gels. Similarity of interaction slopes above the 35–40°C region suggested one reaction mechanism for NAM molecular aggregation in solution and gelation.     

魔芋胶-黄原胶复配体系流变学特性及其凝胶形成动力学分析

为探究魔芋胶与黄原胶2 种食品胶复配使用后的协同作用,以魔芋胶和黄原胶为原料,控制总凝胶质量分 数为1%,以魔芋胶与黄原胶质量比分别为2∶8、4∶6、5∶5、6∶4、8∶2进行复配后,考察复配体系的流变学特性并对 其凝胶形成进行动力学分析。结果表明：魔芋胶-黄原胶复配体系具有假塑性,当魔芋胶的添加比例逐渐增大时, 复配体系黏度系数K增大,流体系数n减小,且复配体系的动态黏弹性质也随着魔芋胶与黄原胶的质量比不同而改 变,当魔芋胶与黄原胶质量比为6∶4时,复配体系的K值达到最大、n值最小,具有最强的假塑性及黏弹性。同时, 魔芋胶与黄原胶的不同质量比对凝胶形成速率有较大影响,当质量比小于6∶4时,凝胶形成显示出较慢的速率,且 形成的凝胶强度较弱;当质量比为6∶4时凝胶形成速率加快,SDRa曲线和G’曲线上升明显,形成的凝胶强度增大, 当质量比继续增加时,凝胶形成速率反而降低。采用阿伦尼乌斯方程对凝胶形成过程中的动力学参数进行拟合,决 定系数均在0.98以上,表现出较高的拟合精度;凝胶形成过程中的活化能在魔芋胶与黄原胶质量比为6∶4时有显著 增加（P＜0.05）,高温段与低温段间的活化能也表现出明显差异。     

Viscosity of guar gum and xanthan/guar gum mixture solutions

The viscosity of diluted guar gum solutions and the viscosity of xanthan and guar gum mixture solutions have been studied. Guar gum solutions showed pseudoplastic behaviour. Apparent viscosity increased with gum concentration and decreased with the temperature at which viscosity was measured. A maximum in the plot of viscosity versus increasing dissolution temperature was observed at 60 °C. This behaviour was related to differences in molecular structure of the polymers solved at different temperatures. Mixtures of xanthan and guar gum showed a higher combined viscosity than that occurring in each separate gum. This synergistic interaction was affected by the gum ratio in the mixture and dissolution temperature of both gums. The effect of polysaccharide concentration (1.0, 1.5 and 2.0 kg m⁻³), xanthan/guar gum ratio (1/5, 4/2, 3/3, 4/2 and 5/1) and dissolution temperature (25, 40, 60 and 80 °C for both gums) on the viscosity of solutions of mixtures were studied. The highest viscosities were observed when 2.0 kg m⁻³ gum concentration was used together with a ratio of xanthan/guar gum of 3/3 (w/w) and dissolution temperature of 40 and 80 °C for xanthan and guar gum, respectively. © 2000 Society of Chemical Industry     

Covalent Bonding in Pressure-Induced Fish Protein Gels

Surimi pastes were gelled by pressure, incubation at 25°C, cooking, or their combination. Differential scanning calorimetry and solubility measurements indicated that myosin denaturation and disulfide bond formation occurred during pressure-induced gelation. Time of pressure treatment had little effect on gel fracture properties. Nondisulfide covalent polymerization of myosin did not appreciably occur during pressure-induced gelation, but was prevalent in gels incubated at 25°C, even when such incubation followed pressure treatment. That combination treatment increased the stress value of cooked gels more than six times, indicating synergy of pressure with the endogenous enzyme transglutaminase, thought to be responsible for gelation of surimi pastes at 25°C.     

Gel properties of silver carp (Hypophthalmichthys molitrix) and chicken mixture gels as affected by setting temperatures

This study aimed to evaluate the effect of setting temperatures (30°C, 35°C, 40°C, 45°C, and 50°C) on gel properties and protein profiles of paste gels derived from silver carp (Hypophthalmichthys molitrix) and chicken meat. The mixture composed of 50% (w/w) chicken meat and 50% (w/w) silver carp meat, and the three paste gels, were assessed based on color, gel strength, TPA, water distribution, chemical interactions, and SDS-PAGE. Chicken gels had better gel properties and a higher content of immobilized water than the mixture or fish gels, regardless of setting conditions. On the other hand, an appropriate setting temperature for the three paste gels promoted aggregation of the myosin heavy chain (MHC) and the formation of hydrophobic interactions and disulfide bonds, which resulted in superior gel properties. Pre-incubation at 40°C enhanced gel properties of fish meat, but pre-incubation at 45°C and 50°C were appropriate for achieving better gels for the mixture and chicken, respectively. These results indicated that there is the potential to obtain mixed products and new meat products by utilizing chicken and fish meat that have improved gel properties.     

Characterization of potato starch fractions and their interaction with hydrocolloids

Commercial potato starch was separated through sedimentation into three fractions of the size < 25, 25–70 and >70 µm estimated with the laser particle meter method and <21.6, 21.7–30.6 and >30.7 µm according to the Sartorius balance method. Amylose and amylopectin content in particular fractions did not depend on the granule size. Number average and weight average molecular weight slightly decreased and phosphorus content increased with the size of granules in the fractions. Starch fractions and, for comparison, non‐fractionated starch were gelatinized in aqueous solutions of arabic, carob, karaya and xanthan gums and carrageenan. Except for the arabic gum, all tested hydrocolloids decreased onset temperature of gelation, T₀, of all starch fractions. Carob and xanthan gums and carrageenan the most remarkably decreased that parameter for large fraction, whereas other gums most considerably decreased T₀ of starch of the medium fraction. Effect of gums upon such parameters of the characteristics of gelation as η_max, η_min and η_25°C depended irregularly on the size of starch granules. In gels from gums and small granules, the role of G′ and G″ module differed from that in gels from the other starch fractions.     

Functional Properties of Myofibrillar Proteins from Cold-Shortened and Thaw-Rigor Bovine Muscles

Prerigor bovine sternomandibularis muscles were stored at 15, 0 and ?29°C to examine cold-shortening and thaw-rigor effects on myofibrillar protein extractability and gelation properties of myofibrils and salt-soluble protein (SSP). Frozen muscle that underwent severe contraction at thawing showed greater protein extractability (35%) than muscles stored at 0 and 15°C (27% extractability). Of the three tempered muscles, thaw-rigor muscle produced the strongest myofibril gel and cold-shortened muscle formed the most elastic SSP gel as determined by dynamic shear and penetration measurements. However, thermally induced changes in gel viscoelastic moduli for all protein samples followed similar patterns. Results indicated that physicochemical changes accompanying muscle contraction affected protein network formation during gelation.     

Sensory quality of low-sugar orange gels with gellan, xanthan and locust bean gums

Effects of reducing the sucrose content (from 55 to 30 ^°Brix in the final product) and of the use of gellan gum or a mixture of gellan, xanthan and locust bean gums (3:1:1) on the mechanical characteristics (maximum rupture force and deformation at rupture) of orange gels prepared with 15% w/w fruit pulp, sucrose and different amounts of hydrocolloids (0.25, 0.4, 0.55 and 0.7% w/w) were studied by uniaxial compression. The concentration of aspartame needed to compensate for sweetness loss was determined by a paired-comparison constant-stimulus method. Sensory characteristics (texture, appearance and flavour) of low-sugar orange gels (30 ^°Brix) with 0.5% w/w aspartame and different amounts (0.55 and 0.7% w/w) of gellan or the mixture of gums were analysed by the free choice profile method in comparison with the high-sucrose reference material (55 ^°Brix and 0.4% w/w gellan). Use of the mixture of gums permitted the obtention of low-sugar orange gels showing mechanical characteristics similar to those of the reference gel, though some differences in texture were perceived. The low-sugar gels were slightly lighter in colour and slightly more bitter and refreshing than the reference sample. Received: 29 November 1995/Revised version: 13 May 1996     

Thermal Aggregation Properties of Duck Salt-Soluble Proteins at Selected pH Values

Thermal aggregation properties of duck breast and leg salt-soluble proteins (SSP) were studied at pH 5.50, 5.75 and 6.00. At pH 5.50, a major transition for breast was observed at 60.3°C and for leg at 41.8°C. At pH 5.75, major transitions at 44.6 and 43.2°C were obtained, respectively, for the breast and leg SSP. Three transitions at 46.0, 53.0 and 59.0°C were exhibited by breast SSP at pH 6.00, whereas only two major transitions at 47.4 and 54.0°C were identified in leg SSP. Changes in transition peak heights and shifts in transition temperatures as a result of pH changes indicated that, depending on fiber type, pH may enhance or suppress the aggregation behavior of specific constituents of the myosin/actomyosin complex, thereby altering the overall aggregation pattern of the protein preparation.