Measurement of dynamic rheology during cooling of honey-invert sugar mixtures by small-deformation oscillatory rheometry

Dynamic rheological properties of honeys in the presence of invert sugar at different levels (0, 10, 20, 30, and 40%) were evaluated by small-deformation oscillatory measurements of dynamic moduli (G′ and G″) during cooling from 0 to ?14°C. The storage modulus (G′) and loss modulus (G″) thermograms of honey during cooling showed more pronounced G″ values when compared to G’, indicating that the presence of invert sugar in honey reduced G″. Such a reduction in G″ can be taken as a good indicator for the adulteration of honey with invert sugar. Therefore, dynamic rheometry for small-deformation oscillatory measurement in the cooling process at sub-zero temperatures appears to be a useful method for detecting the effect of invert sugar adulteration on the structural properties of honey.     

Steady and dynamic shear rheology of glutinous rice flour dispersions

The steady and dynamic shear rheological properties of Korean glutinous rice flour dispersions were evaluated at different concentrations (4, 5, 6, 7 and 8%). Glutinous rice flour dispersions at 25 °C showed a shear‐thinning behaviour (n = 0.487–0.522) with low magnitudes of Casson yield stresses (σ_oc = 0.056–0.339 Pa). The magnitudes of σ_oc, consistency index (K) and apparent viscosity (η_a,100) increased with the increase in concentration. The power law model was found to be more suitable than the exponential model in expressing the relationship between concentration and apparent viscosity. The apparent viscosity over the temperature range of 25–70 °C obeyed the Arrhenius temperature relationship, with high determination coefficients (R² = 0.982–0.998), indicating that the magnitudes of activation energies (E_a) were in the range of 9.05–11.89 kJ mol^?1. A single equation, combining the effects of temperature and concentration on η_a,100, was used to describe the flow behaviour of glutinous rice flour dispersions. Magnitudes of storage (G′) and loss (G′′) moduli increased with the increase in concentration and frequency. Magnitudes of G′ were higher than those of G′′ over most of the frequency range.     

Studies on fish and pork paste gelation by dynamic rheology and circular dichroism

ABSTRACT:  The muscle paste of fish, pork, and their mixtures were prepared to study the gelling characteristics by dynamic rheological measurement. The gelation mechanisms of muscle paste were also investigated by circular dichroism. Gel formation of fish paste occurred in 2 steps of 5 to 35 and 51 to 90 °C respectively, while pork paste mainly in 1 step of 49 to 72 °C. Gel formation was relative to the α-helix unfolding of myosin, which responded the melting temperatures of 40 and 50 °C for fish myosin and 50 and 60 °C for pork myosin, respectively. Alpha-helix unfolding of myosin was beneficial for gel formation. During gel formation, G ' of muscle paste was linearly related to α-helical content of myosin. The interactions of fish and pork proteins at high temperature (>35 °C) could change the gel forming characteristics of muscle paste. Mixed paste exhibited a similar gelation pattern to individual fish paste with 2 visible increases in G '. Addition of pork could suppress the breakdown of fish gel structure at approximately 50 °C. Mixing pork and silver carp in a certain ratio could improve the gel properties of silver carp products.     

The effect of shear on the rheology and structure of heat‐induced whey protein gels

The influence of mechanical shearing on the small deformation properties and microstructure of heat‐induced whey protein gel has been studied. The viscoelastic properties of these gels at different concentrations of 10% and 20% (w/w) exposed to different shear rates of 0, 50, 100, 200 and 500 s^?1 during gelation were measured using dynamic oscillatory rheometry. The structure of both the shear treated and unsheared gels was then investigated using light microscopy. The results showed that the storage modulus of the gels at both concentrations was increased by increasing the shear rate exposure during gelation while the shear‐treated gels were more elastic and showed frequency‐independent behaviour. As the total protein concentration of the gel increased, the viscoelastic properties of the gels also increased significantly and the gels showed greater elasticity. The gels obtained from the higher shear rate exposure were stronger with higher elastic moduli at both protein concentrations. Images of the gels obtained using light microscopy showed that shearing resulted in phase separation and some aggregation in the structure of the gels at both concentrations. However, the shearing rates applied in this study were not enough to cause aggregation breakdown in the gel network.     

Enzyme catalyzed oxidative gelation of sugar beet pectin: Kinetics and rheology

Sugar beet pectin (SBP) is a marginally utilized co-processing product from sugar production from sugar beets. In this study, the kinetics of oxidative gelation of SBP, taking place via enzyme catalyzed cross-linking of ferulic acid moieties (FA), was studied using small angle oscillatory measurements. The rates of gelation, catalyzed by horseradish peroxidase (HRP) (EC 1.11.1.7) and laccase (EC 1.10.3.2), respectively, were determined by measuring the slope of the increase of the elastic modulus (G′) with time at various enzyme dosages (0.125–2.0 U mL⁻¹). When evaluated at equal enzyme activity dosage levels, the two enzymes produced different gelation kinetics and the resulting gels had different rheological properties: HRP (with addition of H₂O₂) catalyzed a fast rate of gelation compared to laccase (no H₂O₂ addition), but laccase catalysis produced stronger gels (higher G′). The main effects and interactions between different factors on the gelation rates and gel properties were examined in response surface designs in which enzyme dosage (0.125–2.0 U mL⁻¹ for HRP; 0.125–10 U mL⁻¹ for laccase), substrate concentration (1.0–4.0%), temperature (25–55 °C), pH (3.5–5.5), and H₂O₂ (0.1–1.0 mM) (for HRP only) were varied. Gelation rates increased with temperature, substrate concentration, and enzyme dosage; for laccase catalyzed SBP gelation the gel strengths correlated positively with increased gelation rate, whereas no such correlation could be established for HRP catalyzed gelation and at the elevated gelation rates (>100 Pa min⁻¹) gels produced using laccase were stronger (higher G′) than HRP catalyzed gels at similar rates of gelation. Chemical analysis confirmed the formation of ferulic acid dehydrodimers (diFAs) by both enzymes supporting that the gelation was a result of oxidative cross-linking of FAs.     

不同品种花生蛋白流变特性的研究

对8种花生蛋白的流变特性进行了探讨。静态流变特性测定结果表明,8种花生蛋白的流变模型为幂率模型,均为非牛顿流体。在同样的流动方式下,忠毅9616的黏度最大,花育16次之,其他几种变化无明显差别。动态流变特性测定结果表明,随着温度的升高,不同品种花生蛋白的贮藏模量、损失模量以及损失系数均呈现出不同的变化趋势。其中,忠毅9616品种蛋白的贮藏模量最大,红珍珠次之,花育16最小;红珍珠、奇山208、的损失模量高于其他几种,花育16最低;忠毅9616的损失系数最小,奇山208最大。     

酸奶对玉米淀粉流变特性的影响

乳酸菌发酵能够产生淀粉酶。为考察含有活性乳酸菌的酸奶对淀粉黏弾特性的影响,本文以玉米淀粉为原料,分别加入1%（v/v）的蒙牛酸奶、完达山酸奶、伊利酸奶,并在37℃保温1小时;用流变仪研究发酵后玉米淀粉的流变学性质。实验结果表明：剪切流变曲线服从Herschel-Bulkley模型 （R>0.90）。屈服应力τ0、粘度系数k增加,流动指数n减小（n<1）,显示发酵后的玉米淀粉仍然是非牛顿、屈服假塑性流体。震荡流变曲线显示添加酸奶的样品组的贮能模量G''与损耗模量G''均大于空白组、且均随着剪切频率的增大而增大。本项研究首次发现经乳酸菌发酵的玉米淀粉,具有更高的黏弹特性。     

Lactoperoxidase Effects on Rheological Properties of Yogurt

A mixed culture ( Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus ) was inoculated into reconstituted skim milk and incubated. When 0.45 Unit/g or more of lactoperoxidase (LPO) was added, the yogurts had softer and smoother texture than untreated yogurt. The apparent viscosity of yogurt was also reduced by addition of LPO. The storage modulus (G') of the gel of LPO-treated yogurt decreased but the frequency-dependency remained unchanged. The amount of exopolysaccharide or degree of proteolysis in yogurt was not changed by addition of LPO.     

解冻方式对冻结鸡汤流变与蛋白质的影响

探究解冻方式(微波、高温水浴、室温空气解冻)对冻结鸡汤(-20,-40℃冻结)流变与蛋白质的影响。结果表明:冻结鸡汤解冻后汤体具有假塑性;相同剪切速率条件下,-20℃冻结鸡汤室温空气解冻后黏度和剪切应力均大于-40℃冻结鸡汤,但微波、高温水浴解冻后的黏度和剪切应力趋势线几乎完全重合,且均低于室温空气解冻组。同一冻结鸡汤室温空气解冻后的胶原蛋白含量、可溶性蛋白含量、巯基含量和乳化活性均显著高于其他解冻方式(P0.05),但羰基含量显著低于其他解冻方式(P0.05)。因此,不同解冻方式的冻结鸡汤流变和蛋白质变化较大,且微波、高温水浴解冻对冻结鸡汤的影响比室温空气解冻更大。     

Influence of intrinsic and extrinsic factors on rheology of pectin–calcium gels

Pectin was selectively demethoxylated by use of NaOH or pectinmethylesterase from plant or fungal origin in order to produce a library of pectins with varying degree and pattern of methoxylation. In addition, pectin was chemically depolymerised by a heat treatment. The resulting pectin products were characterised by studying the degree and pattern of methoxylation and the extent of depolymerisation. The pattern of methoxylation was estimated quantitatively by determining the “degree of blockiness” (DB and DB_abs). Pectin–calcium gels were prepared at varying concentrations of both components. Rheological properties of these gels were studied by performing small deformation oscillatory tests. Gel strengths were better explained by the pattern of methoxylation than by the degree of methoxylation. The relation between rheological properties and calcium or pectin concentration depended on the pattern of methoxylation. Depolymerisation had a detrimental effect on gel strength, especially at low calcium concentration.     

Molecular forces involved in heat-induced pea protein gelation: Effects of various reagents on the rheological properties of salt-extracted pea protein gels

The molecular forces involved in the gelation of heat-induced pea protein gel were studied by monitoring changes in gelation properties in the presence of different chemicals. At 0.3 M concentration, sodium thiocyanate (NaSCN) and sodium chloride (NaCl) showed more chaotropic characteristic and enhanced the gel stiffness, whereas sodium sulfate (Na₂SO₄) and sodium acetate (CH₃COONa) stabilized protein structure as noted by increasing denaturation temperatures (T_d) resulting in reduced storage moduli (G′). To determine the involvement of non-covalent bonds in pea protein gelation, guanidine hydrochloride (GuHCl), propylene glycol (PG), and urea were employed. The significant decrease in G′ of pea protein gels with the addition of 3 M GuHCl and 5 M urea indicated that hydrophobic interactions and hydrogen bonds are probably involved in pea protein gel formation. The increase in G′ with increasing PG concentration (5–20%), demonstrated hydrogen bonds and electrostatic interaction involvement. No significant influence was observed on G′ with addition of different concentrations of β-mercaptoethanol (2-ME), low levels of dithiothreitol (DTT), and up to 25 mM N-ethylmaleimide (NEM), which indicated that disulfide bonds are not required for gel formation, but data at higher DTT and NEM concentrations and slow cooling rates showed a minor contribution by disulfide bonds. Reheating and recooling demonstrated that gel strengthening during the cooling phase was thermally reversible but not all the hydrogen bonds disrupted in the reheating stage were recovered when recooled.     

低温贮藏对鸡胸肉肌原纤维蛋白结构及热诱导凝胶性能的影响

目的 研究4℃(冷藏)与-18℃(冷冻)贮藏条件对鸡胸肉肌原纤维蛋白(myofibrillar protein, MP)结构及热诱导凝胶性能的影响。方法 通过测定总巯基、钙离子ATP酶(calcium-ATPase, Ca2+-ATPase)活性、表面疏水性、凝胶质构、保水性等指标衡量MP结构及凝胶特性的变化,并从分子间作用力及蛋白质构象角度阐述贮藏条件对MP热诱导凝胶机制的影响。结果 在4℃与和-18℃贮藏环境下,随着贮藏时间的延长,MP总巯基含量减少,表面疏水性上升, Ca2+-ATPase酶活性降低。其次, MP热诱导凝胶中离子键及氢键作用力也随贮藏时间的延长而呈下降趋势,而疏水作用力呈上升趋势;凝胶中的α-螺旋和β-折叠含量呈下降趋势,而β-转角与无规则卷曲含量呈上升趋势。结论 低温贮藏期间MP结构发生劣变,蛋白凝胶结构由有序转向无序结构,导致凝胶质构、保水性下降;相较4℃贮藏,-18℃能够更好地长时间维持MP结构和凝胶特性。     

Rheological Characteristics and Morphology of Dialdehyde Starch/Meat Composites during Heating

ABSTRACT:  Dialdehyde starch (DAS) was added to pork ham batter. The effects of DAS on the meat protein gel during heating were investigated using thermal and rheological analyses. In this study, the degree of DAS oxidation was controlled by the reaction time. The DSC thermogram showed that increasing the degree of oxidation resulted in DAS having a higher gelatinization temperature and lower heat absorption. In dialdehyde starch/meat (DAS/M) composites, meat protein reduced the availability of water to starch and raised the gelatinization temperature and heat absorbed by the composites. The G '_max of the composites was greater than the linear combination of their components. The rheological properties of DAS were a major factor affecting the properties of its composites. Scanning electron microscopy and light microscopy with the aid of histologic technique revealed the network and distribution of DAS and DAS/M composites. The protein matrix formed the backbone of the network and gelatinized starch was trapped in the protein structure.     

壳聚糖溶液的Cross拟合和动态粘弹性分析

在25℃条件下运用Cross模型对壳聚糖溶液（0.005～0.025g/mL）的流动曲线进行了拟合,运用频率扫描和复合波温度扫描分析了壳聚糖溶液的动态粘弹性。结果表明:壳聚糖溶液（0.005～0.025g/mL）符合流变学的Cross模型,且浓度越高,其临界剪切变稀速率越小;损耗模量（G″）始终大于储能模量（G’）,且随着扫描频率的增大G″和G’值逐渐接近,低频率扫描条件下表现为类似于流体的粘弹性行为,高频率扫描下有网状交联结构形成。复合粘度随着温度的升高和频率的增大而降低,在温度和振荡频率同时变化的情况下建立了粘度-温度-频率的流变学模型。      

魔芋葡甘聚糖与大豆分离蛋白共混形成凝胶过程中的相互作用力研究

为研究魔芋葡甘聚糖(KGM)与大豆分离蛋白(SPI)在水和碱性促凝剂存在条件下的相互作用力,采用红外光谱、扫描电子显微镜和化学方法等手段进行分析。结果表明:在KGM-SPI共混凝胶形成过程中氢键为主要的分子作用力,其次为较弱的静电作用。碱性凝固剂的加入可使凝胶的韧弹性更好,氢键作用更强。此外,交互作用的强弱还与KGM和SPI的含量及配比密切相关。魔芋葡甘聚糖与大豆分离蛋白分子间可依靠多点氢键作用形成热不可逆性凝胶。     

Stabilization of oil-in-water emulsions by enzyme catalyzed oxidative gelation of sugar beet pectin

Enzyme catalyzed oxidative cross-linking of feruloyl groups can promote gelation of sugar beet pectin (SBP). It is uncertain how the enzyme kinetics of this cross-linking reaction are affected in emulsion systems and whether the gelation affects emulsion stability. In this study, SBP (2.5% w/v) was mixed into an oil-in-water emulsion system (4.4% w/w oil, 0.22% w/w whey protein, pH 4.5). Two separate, identically composed, emulsion systems were prepared by different methods of preparation. The emulsions prepared separately and subsequently mixed with SBP (referred as Mix A) produced significantly larger average particle sizes than the emulsions in which the SBP was homogenized into the emulsion system during emulsion preparation (referred as Mix B). Mix B type emulsions were stable. Enzyme catalyzed oxidative gelation of SBP helped stabilize the emulsions in Mix A. The kinetics of the enzyme catalyzed oxidative gelation of SBP was evaluated by small angle oscillatory measurements for horseradish peroxidase (HRP) (EC 1.11.1.7) and laccase (EC 1.10.3.2) catalysis, respectively. HRP catalyzed gelation rates, determined from the slopes of the increase of elastic modulus (G′) with time, were higher (P < 0.05) than the corresponding laccase catalyzed rates, but the final G′ values were higher for laccase catalyzed gels, regardless of the presence of emulsions or type of emulsion preparation (Mix A or Mix B). For both enzymes, rates of gelation in Mix A were higher (P < 0.05) than in Mix B, and higher stress was needed to break the gels in Mix A than in Mix B at similar enzyme dosage levels. These differences may be related to a lower availability of the feruloyl groups for cross-linking when the SBP was homogenized into the emulsion system during preparation.     

Structural and rheology properties of pea protein isolate-stabilised emulsion gel: Effect of crosslinking with transglutaminase

The microstructures and characteristics (water holding capacity (WHC) and rheological properties) of pea protein isolate (PPI) emulsion gels produced via transglutaminase (TGase) with different oil-weight fractions (φ, 20%~50%) were studied in the present work. The results showed that the WHC and gel strength (storage modulus) of PPI emulsion gel were raised with increasing of φ. Simultaneously, the proteins entrapped within the network gradually increase due to the enzymatic treatment, which resulted in a tighter internal structure of emulsion gel. At high oil-weight fractions (e.g. 50%), the network of the emulsion was essentially a coarse chain of particulate, mainly forming a ‘close-knit’ oil droplet. Therefore, the gelation mechanism is related to the state of proteins in the system, which are divided into proteins adsorbed and unadsorbed on the interface. The results will be of significant assistance in comprehending the theories of the gelation process and the protein emulsion gels immobilisation by the enzyme.