SMALL AMPLITUDE OSCILLATORY SHEAR STUDIES ON MOZZARELLA CHEESE PART II. RELAXATION SPECTRUM

The frequency dispersion of dynamic mechanical spectra of a low-moisture, part-skim and a low-fat, part-skim Mozzarella cheese are presented. Small amplitude oscillatory shear measurements within the linear viscoelastic range (0.05% strain) were made over 12 weeks of storage. Proteolysis during storage led to softening of the cheeses and thus decreases in storage (G';) and loss (G") moduli. Master curves (at a reference temperature of40C) were obtained by shifting the temperature-dependent frequency dispersion of storage modulus. There was no significant change in G' after 4 weeks of aging. The variation of relaxation time and viscosity spectrum of both cheeses with age were obtained from the master curves using the generalized Maxwell model and nonlinear regression analysis. With maturation the viscosity distribution of corresponding Maxwell elements shifted towards smaller values, indicating that cheeses become softer and melt more easily.     

Effect of Ca and P Content,Residual Lactose,and Salt-to-Moisture Ratio on the Model Parameters of Process Cheese Linear Viscoelastic Properties

The main aim of this study was to investigate the influence of two different levels (high and low) of Ca and P (calcium and phosphorous) content, residual lactose, and salt-to-moisture (S/M) ratio on viscoelastic properties of eight different process cheeses. Frequency sweep was performed at 750 Pa on all experimental process cheese samples to determine the power-law model parameters. Process cheeses with high Ca and P content and high S/M ratio were significantly harder (P < 0.05) (higher storage and loss modulus, and lower creep and recovery compliance) compared to low Ca and P content and low S/M ratio process cheeses. However, no significant difference was observed (P > 0.05) for power-law parameters between high/low residual lactose content process cheese samples. Six-element Kelvin-Voigt model was used to predict the creep compliances for eight different process cheeses. This model described the affect of above treatment's retardation spectra (compliances, viscosities, and retardation times) obtained from creep tests. Both of these measurements indicated the similar trend on linear viscoelastic properties for eight different process cheeses.     

EVALUATING RHEOLOGICAL PROPERTIES OF MOZZARELLA CHEESE BY THE SQUEEZING FLOW METHOD

We adapted the squeezing flow technique to make compression and relaxation tests on Mozzarella cheese at temperatures ranging from 30 to 60C during one month of refrigerated storage. The deformability modulus of the cheese decreased with aging and temperature but increased with deformation rate. The average decrease in the deformability modulus was 0.4 kPa/day and 0.5 kPa/C. Relaxation data also indicated a continuous increase in viscous character of Mozzarella with aging and temperature. Apparent relaxation time was less than 10 s. Relaxation parameters showed a strong temperature dependency in the range of 10-60C. Lubricated squeezing flow data showed that the resistance of Mozzarella to flow decreased with aging and temperature indicating an increased meltability.     

Use of time–temperature superposition to study the rheological properties of cheese during heating and cooling

The objective of this study was to investigate the time–temperature superposition behaviour of the rheological properties of cheese during heating and cooling. A standard part‐skim Mozzarella cheese and a fat‐free cheese were used for the study. Fourier transform mechanical spectroscopy was used to simultaneously study the rheological properties over a range of frequencies from 0.08 to 8 Hz while samples were being heated from 10 to 90 °C or cooled from 90 to 10 °C at the rate of 1 °C min^?1. Master curves of storage modulus (G′), loss modulus (G′′) and loss tangent were obtained using a reference temperature of 70 °C.     

Variations in Dextrose Equivalent and Dynamic Rheology of Dextrin Obtained by Enzymatic Hydrolysis of Edible Canna Starch

We aimed to evaluate the dextrose equivalent and the dynamic rheological parameters of dextrin obtained by hydrolysis of edible canna starch by using α-amylase enzyme. We found that the dextrose equivalent value and dynamic rheological properties, as presented by storage and loss modulus (G? and G″) values, varied with the incubation time (1, 3, and 5 h) and α-amylase concentration (0.03, 0.04, 0.05, and 0.06% w/w). Increase in the incubation time and α-amylase concentration increased the dextrose equivalent from 9.0 ± 0.2 to 21.3 ± 1.9 and decreased the storage modulus (G′) from 3747.4 to 18.0 Pa and the loss modulus (G″) from 659.4 to 5.5 Pa at 25°C. Meanwhile, G′ decreased from 27781.0 Pa to 11313.1 Pa and G″ decreased from 6647.2 Pa to 1826.4 Pa at 95°C.     

Linear Viscoelastic Properties of Regular- and Reduced-Fat Pasteurized Process Cheese During Heating and Cooling

The rheology of process cheese during heating and cooling was examined by measuring the transient and dynamic linear viscoelastic properties of regular fat, lower moisture and an 80% reduced-fat, higher moisture pasteurized process cheese from 10 to 50°C. The dynamic (stress and frequency sweep) and transient (creep and recovery) rheological properties of the reduced-fat process cheese were found to be higher than that of regular-fat process cheese, indicating that fat content changed rheological properties more than moisture content. The temperature-dependent frequency dispersions of storage and loss moduli (dynamic mechanical spectra) were fitted with a power-law model, and master curves (at a reference temperature of 30°C) and shift factors were obtained by shifting the temperature-dependent frequency dispersion of dynamic mechanical spectra. The relaxation spectra (moduli, viscosities and relaxation times) of both cheeses were obtained from the master curves using the generalized Maxwell model and nonlinear regression. The viscosity distribution of corresponding Maxwell model elements were higher for the reduced-fat cheese by a factor of 1.6–4.7 compared to the regular-fat cheese, indicating that the higher moisture content in the reduced-fat process cheese did not loosen the protein matrix or soften the cheese even though higher moisture is recommended to cheese manufacturers in order to compensate for some textural defects in reduced-fat cheeses.     

Nuclear magnetic resonance study of water mobility in pasta filata and non-pasta filata mozzarella

Changes in molecular mobility of water in pasta filata and non-pasta filata Mozzarella cheeses were investigated during the first 10 d of storage using nuclear magnetic resonance (NMR) relaxation techniques. Water in pasta filata Mozzarella was classified into two fractions by spin-spin relaxation times, T21 and T22, and corresponding proton intensities, A1 and A2, representing low and high molecular mobility, respectively. Increase in A1 (and decrease in A2) suggested that, there was a redistribution of water from more- to less-mobile fraction (from T22 to T21 fraction) during the first 10 d of storage. The NMR data did not indicate the two-state behavior of water molecules in non-pasta filata Mozzarella. However, the T2 values of non-pasta filata Mozzarella were comparable to the T21 values of pasta filata Mozzarella indicating that the molecular mobility of water in non-pasta filata Mozzarella is comparable to that of the less mobile water fraction in pasta filata Mozzarella. Generally, T2 and T1 values of pasta filata and non-pasta filata Mozzarella cheeses increased during the 10-d storage. This is believed to be due to structural changes in the protein matrix.     

Effect of frozen storage on physical properties of pasta filata and nonpasta filata Mozzarella cheeses

The effects of 1) ripening 2, 7, and 14 d at 7 degrees C before freezing; 2) tempering 7, and 14 d at 7 degrees C after freezing; and 3) frozen storage for 1 and 4 wk at -20 degrees C, on the meltability, stretchability, and microstructure of pasta filata and nonpasta filata Mozzarella cheeses were investigated. Cheeses were cut into 5 x 10 x 7-cm blocks and vacuum-sealed 1 d after manufacture. The results were compared to the corresponding results obtained with unfrozen control samples, aged at 7 degrees C between 2 and 21 d. The changes in physical properties of frozen-stored pasta filata and nonpasta filata Mozzarella cheeses were consistent with critical damage to the cheese microstructure as compared to the unfrozen control samples. Generally, aging before and tempering after freezing resulted in increased meltability of both frozen-stored pasta filata and nonpasta filata Mozzarella cheeses. The stretchability of frozen-stored pasta filata Mozzarella cheese increased during tempering, but that of nonpasta filata Mozzarella cheese decreased during aging and tempering. In most cases, one-week frozen stored pasta filata Mozzarella cheese had higher meltability and stretchability than 4-wk frozen-stored sample. For 1-wk frozen-stored nonpasta filata Mozzarella cheese, the meltability increased but stretchability decreased when it was frozen-stored for 4 wk.     

THE EFFECT OF TEMPERATURE ON THE RHEOLOGY OF BUTTER, A SPREADABLE BLEND AND SPREADS

The texture of lipid-based food materials is an important topic for investigation. In this study, the rheological properties of five edible fats were determined. A puncture test was performed to investigate the rheological properties of the food materials at 5C and at 19C using a texture analyzer. The force-displacement measurements were converted to stress–strain by assuming incompressibility of edible fat food materials in a linear viscoelastic region (LVR). Young's modulus of each edible fat was calculated using stress–stain curves in a LVR. Shear elastic moduli of edible fats in a LVR were obtained using a rheometer. Further to that the effect of temperature on storage modulus and loss modulus and creep test were obtained using a rheometer. The tests showed good correlation between Young's modulus and shear elastic modulus for each material. The mechanical properties correlated well with the structural properties of each of the materials.

PRACTICAL APPLICATIONS

The texture of butter, blends and spreads is determined by temperature, rheological properties, processing conditions and the composition of the material. Our research investigated the effect of temperature on the rheological properties of these foods. The results may be used to model the relationship between the microstructure and mechanical properties of the fat crystal network.     

CHARACTERISATION OF A COMMERCIAL SOY ISOLATE BY PHYSICAL TECHNIQUES

The mechanical features of a partially denatured commercial soy isolate (PP 500E) have been explored for comparison with data available on the gelation characteristics of native globular proteins and to improve the understanding of its textural properties as a structuring ingredient in the production of low fat products. The soy sample was reconstituted at 30C and networks were developed either during cooling to 5C or on heating to 90C (complete denaturation of the protein) followed by cooling to 5C. Throughout the course of experimentation, dynamic oscillatory (time, temperature, frequency and strain sweeps) and creep testing (in aqueous or urea solutions) measurements were recorded. Reduction in the thermal energy of the system causes a monotonic increase in storage modulus (G′) whereas the temperature rise results in equilibrium G′ values well below the elastic response observed at 30C. The absence of a positive thermal transition, observed in the gelation of native globular proteins, indicates a different mechanism for structure formation in commercial soy isolates. Application of the cascade treatment to the concentration dependence of the storage modulus argues that the heated and cooled networks possess a higher degree of bond permanency than their cooled-only counterparts. Mechanical spectra in combination with the pattern of network breakage at high deformations suggests that disulphide bonds participate in the network formed by totally denatured soy protein (heated and cooled samples). Inclusion of urea in the aqueous preparations destabilises the predominantly physical forces of attraction in the unheated gels. By contrast, the heated and cooled samples achieve an equilibrium deformation whose storage modulus can be employed in the constitutive equation of rubber elasticity theory. On that basis the number of disulphide bridges per molecule was found to vary between 2.0 and 2.03. This result is consistent with the “string of beads” model proposed for the three-dimensional structure of globular protein gels, where a dendric network is built by the occasional cross-linking of corpuscular strands.     

Viscoelastic Characterization of Sage Seed Gum

Wild sage seed is a small, rounded, and mucilaginous seed, which comes from Salvia macrosiphon. The viscoelastic behavior of sage seed gum, at different concentrations (0.5–2%, w/w), was examined by measuring the transient (in-shear structural recovery and creep/recovery tests) and dynamic (stress and frequency sweeps) rheological properties. The mechanical spectra showed typical weak gel behavior at all concentrations, with storage modulus higher than loss modulus, and little variation with frequency. Both moduli greatly increased with increasing the concentration, and the concentration dependency was well described by the power-law model. The loss tangent was increased slightly with increasing the frequency in the range of 0.25–0.67, although it was not affected by an increase in gum concentration. Moreover, the complex viscosity was found to increase with the increase of sage seed gum concentration and to decrease linearly with the increase of frequency. All samples showed typical viscoelastic response to stress in creep/recovery tests, with recoverable strain increasing in direct proportion to sage seed gum concentration. Creep curves were adequately fitted with a Burger model of four parameters. The elastic and viscous contributions to the general viscoelastic behavior were analyzed through the obtained parameters. The concentration had no specific effect on the in-shear recovery properties of sage seed gum gels, and the gel structure was highly recovered after applying shear. The results of this article indicated that sage seed gum may offer an excellent alternative for commercial gums as a thickening/gelling agent.     

A Viscoelastic Model for Honeys Using the Time–Temperature Superposition Principle (TTSP)

The viscoelastic parameters storage modulus (G′) and loss modulus (G″) were measured at different temperatures (5 °C, 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, and 40 °C) using oscillatory thermal analysis in order to obtain a viscoelastic model for honey. The model (a 4th grade polynomial equation) ascertains the applicability of the time–temperature superposition principle (TTSP) to the dynamic viscoelastic properties. This model, with a regression coefficient higher than 0.99, is suitable for all honeys irrespective their botanical origin (monofloral, polyfloral, or honeydew). The activation energy (relaxation“ΔH _a” and retardation “ΔH _b”), and the relaxation modulus fit the model proposed. The relaxation modulus has a 4th grade polynomial equation evolution at all temperatures. The moisture content influences all the rheological parameters.     

Viscoelasticity, texture and ultrastructure of cut apple as affected by sequential anti-browning and ultraviolet-C light treatments

The aim of this work was to analyze the effect of UV-C radiation (fluence: 11.2 kJ/m²), with or without an anti-browning pretreatment containing 1% (w/v) ascorbic acid plus 0.1% (w/v) calcium chloride, on the linear viscoelastic properties (oscillatory shear and creep/recovery), instrumental texture (TPA), sensory texture and ultrastructure (ESEM, TEM) of cut apple. Changes in structural features and viscoelastic parameters were mainly evidenced after refrigerated storage. All samples showed a viscoelastic solid behavior with the storage modulus (G′) dominating the viscoelastic response. Overall, both dynamic moduli decreased, and instantaneous compliance (J₀), decay compliances (J₁ and J₂) and fluidity significantly increased after treatments and storage at 5 °C, while retardation times were in general constant. Fracture properties proved to be the most highly correlated with sensory texture. The test panel only significantly differentiated stored untreated apple from the other samples regarding fracturability and juiciness. Mechanical spectra and creep parameters showed ability to evidence ultrastructural differences (rupture of membranes, swelling of cells, alteration of cell walls) in the surface of cut apples subjected to the different treatments.     

稻米-高筋小麦混合粉面团的静态和动态流变学特性

本实验研究了6 种稻米-高筋混合粉面团的静态和动态流变学特性。结果表明,随着稻米粉添加量的增加,在动态流变频率扫描中,混合面团的储存模量（G’）和损耗模量（G’’）整体呈上升趋势,损耗角正切（tan δ）整体呈规律性下降趋势;在静态流变的蠕变松弛实验中,最大蠕变应变量、最大蠕变柔量和瞬时恢复柔量逐渐减小,零剪切黏度和瞬间恢复比率逐渐增加,表明加入稻米粉后面筋蛋白有所稀释,但稻米粉中的淀粉吸水膨胀相互黏附,且与米蛋白相互作用赋予面团更高的弹性模量和更复杂的内部结构。在动态流变的温度扫描中,糊化温度前后混合面团的黏弹性变化明显,G’和G’’曲线类似淀粉糊化曲线,说明生面团加热的过程中,影响其流变学特性的主要成分为淀粉;降温过程中,稻米粉添加量的影响较小,高温区G’和G’’呈规律性增加,温度低于60 ℃后各项流变指标规律性差;在整个降温的过程中样品均具有类固体的性质。     

RHEOLOGICAL EVALUATION OF MOZZARELLA CHEESE BY UNIAXIAL HORIZONTAL EXTENSION

Rheological properties of low-moisture part-skim Mozarella cheese were evaluated as a function of storage time, test temperature, and deformation rate by uniaxial extension in a horizontal plane. Proteolysis of Mozzarella cheese caused marked decreases in the tensile strength and the deformability modulus, but not in the fracture strain. As the temperature increased from 10 to 40C, the fracture strain increased more than five-fold. The strength and the deformability modulus decreased about 60 and 85%, respectively, as the cheese temperature increased from 10 to 30C. The fracture strain of the cheese did not exhibit a clear trend with the deformation rate in the range of 50–500 mm/min. However, its strength and deformability modulus increased with the increasing deformation rate.     

Rheological Behavior of Frozen and Thawed Low-Moisture, Part-Skim Mozzarella Cheese

Stress relaxation and dynamic profiles of low-moisture, part-skim (LMPS) Mozzarella cheese cylinders refrigerated 14 days (control), frozen and thawed, and stored frozen and refrigerated up to 90 days were compared. Samples were frozen at ?30°C and stored at ?20°C. Thawing and refrigerated storage were at 5°C. Stress relaxation tests were conducted at 20°C and dynamic spectrometry at 20°C and 60°C. The frozen and thawed Mozzarella cheese tested at 20°C became harder and more elastic with storage time, while refrigerated stored samples became softer and more elasticoviscous with time. Upon melting, both go-day-frozen and go-day-refrigerated cheeses were less elastic and less viscous than 14-day-refrigerated samples.     

Effect of freezing and frozen storage on microstructure of Mozzarella and pizza cheeses

Scanning electron microscopy was used to assess the effect of aging before (2, 7, and 14 days at 7 °C) or tempering after (1, 7, and 14 days at 7 °C) freezing, and frozen storage (1 and 4 weeks at −20 °C) on protein matrix of pasta filata Mozzarella and non-pasta filata pizza cheeses using unfrozen samples as controls. Pores and ruptures of reticular structure were observed in frozen-stored pasta filata Mozzarella cheese protein matrix, but cracks and clumps of bacteria were found in frozen-stored non-pasta filata pizza cheese. No obvious differences were discernable between the microstructures of pasta filata Mozzarella cheeses frozen stored 1 and 4 weeks. Formation of the reticular structure in frozen-stored pasta filata Mozzarella cheese progressed during tempering. Microstructure of non-pasta filata pizza cheese frozen stored for 4 weeks contained more extensive cracking and more areas of clumps of bacteria than that was frozen stored for 1 week. Aging of cheese before frozen storage was considered responsible for microstructural cracking; fewer cracks were found in the frozen-stored cheese tempered 1 and 2 weeks, but the clumps of bacteria were still observed.     

Thermal gelation of globulin from Phaseolus angularis (red bean)

The heat-induced gelation properties of red bean globulin (RBG) were studied under the influence of salts and several protein structure perturbants. The viscoelastic properties of the gels were evaluated by small amplitude oscillatory tests and creep experiments. Gel structure developed progressively when a protein dispersion (≈10% w/v) was heated from 25 to 95 °C, and both the storage modulus (G′) and loss modulus (G″) increased rapidly during cooling. The addition of NaCl at lower concentrations led to increases in G′ and G″ values, with decreased creep compliance, suggesting higher viscoelasticity. At higher salt concentrations, viscoelasticity was decreased, and the optimum NaCl concentration to produce maximum gel rigidity was 0.2 M. Sodium dodecyl sulfate and urea caused more pronounced reduction of the gel moduli than dithiothreitol and N-ethylmaleimide. The data suggest that hydrophobic interactions and hydrogen bonding play an important role in heat-induced gelation, while electrostatic interactions and a balance of attractive–repulsive forces are also important. The gels formed at 95 °C exhibited a homogenous microstructure with extensive cross-links and sheet-like network structures.     

Factors regulating cheese shreddability

Two sets of cheeses were evaluated to determine factors that affect shred quality. The first set of cheeses was made up of 3 commercial cheeses, Monterey Jack, Mozzarella, and process. The second set of cheeses was made up of 3 Mozzarella cheeses with varying levels of protein and fat at a constant moisture content. A shred distribution of long shreds, short shreds, and fines was obtained by shredding blocks of cheese in a food processor. A probe tack test was used to directly measure adhesion of the cheese to a stainless-steel surface. Surface energy was determined based on the contact angles of standard liquids, and rheological characterization was done by a creep and recovery test. Creep and recovery data were used to calculate the maximum and initial compliance and retardation time. Shredding defects of fines and adhesion to the blade were observed in commercial cheeses. Mozzarella did not adhere to the blade but did produce the most fines. Both Monterey Jack and process cheeses adhered to the blade and produced fines. Furthermore, adherence to the blade was correlated positively with tack energy and negatively with retardation time. Mozzarella cheese, with the highest fat and lowest protein contents, produced the most fines but showed little adherence to the blade, even though tack energy increased with fat content. Surface energy was not correlated with shredding defects in either group of cheese. Rheological properties and tack energy appeared to be the key factors involved in shredding defects.     

Effects of Starter Culture and Coagulating Enzymes on Viscoelastic Behavior and Melt of Mozzarella Cheese

ABSTRACT: Mozzarella cheeses were made with a single culture (SC) or a mixed culture (MC) using 1x or 6x of cheese coagulants chymosin or Cryphonectria parasitica (CP). Melt area increased only by approximately 80% in cheeses made with SC against 230% in the cheeses made with MC after 30 d of storage. Soluble nitrogen was also higher in MC cheeses as compared to SC cheeses. Both the elastic (G') and the viscous (G") modulus decreased with storage. Decrease in both moduli was greater in the MC cheeses at 6× enzyme level compared to SC cheeses at 1× enzyme level. The synergism between coagulating enzyme and starter culture was beneficial, which improved melt and flow of Mozzarella cheese and had profound effects on the viscoelastic properties of Mozzarella cheese.