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.     

RHEOLOGICAL AND CHEMICAL PROPERTIES OF MOZZARELLA CHEESE

Dynamic viscoelastic parameters and chemical properties of Mozzarella cheese produced using a "no-brine" cheese making method with 3 different cooking temperatures (38, 41, and 44C) were determined. Samples were stored for 3 weeks at 4C before dynamic mechanical analysis at 22C. G', G" and tan δ were 5.8 – 6.4 × 10⁵ dyne/cm², 1.9 – 2.1 × 10⁵ dyne/cm², and 0.33 – 0.35, respectively, at 1% strain and 10 rad/s. The percentage of intact α_s-casein and β-casein were 38–40% and 33–35% of total protein in the cheese, respectively. The range of cooking temperatures used in this experiment had little effect on dynamic viscoelastic properties or the amount of intact protein for the cheese.     

DYNAMIC RHEOLOGICAL PROPERTIES OF NATURAL AND IMITATION MOZZARELLA CHEESE

Suitability of Mozzarella cheese for various products involves the measurement of rheological properties of the cheese related to its meltability. The rheology in this work is determined dynamically with a Rheometrics RDA 700 mechanical spectrometer using 25 mm diameter parallel plates fabricated from aluminum. Bonding the cheese specimen directly to the plates with cyanoacrylate ester adhesive proved the most effective in countering the problem of specimen slip. Viscosity proved sensitive to addition of calcium casenate, following an Arrhenius relationship with temperature. Both elastic and viscous components of the shear modulus increased with a 1% addition but a 2% addition decreased the elastic component below that observed for natural Mozzarella under the same conditions.     

RHEOLOGICAL PROPERTIES OF UF-FETA CHEESE DETERMINED BY UNIAXIAL COMPRESSION AND DYNAMIC TESTING

Rheological characteristics of three Feta cheeses produced from ultrafiltered milk (UF-Feta cheeses) with different textures were evaluated using uniaxial compression and dynamic testing (strain and frequency sweeps). Stress at fracture was 20–46 kPa, Hencky strain at fracture was 0.20–0.35, modulus of deformability was 176–465 kPa, and work up to fracture was 4.4–6.7 kj/m³, depending on the type of cheese and the strain rate. Stress at a given strain, and stress at fracture increased with strain rate: the slope of the log (stress at fracture) versus log(in-itial Hencky strain rate) plot was 0.06–0.21, indicating a partially viscous behavior. Stress at fracture discriminated between all three Feta textures, and Hencky strain at fracture discriminated a Tin Feta texture from two Brick Feta textures at every compression rate. In dynamic testing the complex modulus was 40–173 kPa, and tan (δ) was 0.17–0.25 depending on the type of cheese and the frequency of oscillation. The slope of log(complex modulus) or log(storage modulus) versus log (frequency) was 0.12–0.14, and the slope of log(loss modulus) versus log (frequency) was 0.07–0.11 for all three types of cheese. The complex modulus from strain and frequency sweeps in the dynamic testing distinguished the Tin Feta texture from the Brick Feta textures, and the phase angle (δ) measured in strain sweep could differentiate the Blue Brick Feta texture from the Red Brick Feta texture in the strain interval 0.0003–0.024.     

RHEOLOGICAL PROPERTIES OF A PROGEL FORMED FROM A SOY-GELATIN MOZZARELLA CHEESE ANALOG

Progels formed from aqueous dispersions of an imitation mozzarella cheese containing soy protein isolate, gelatin, fat and GFS gum (mixture of xanthan, guar and locust bean gums) at a total solids of 8% w/v exhibited pseudoplastic behavior. The data could be fitted to the power law equation for shear rates above 100 s⁻¹. Below this shear rate, deviations from the model were observed such that the experimental apparent viscosity (v_a) was greater than the predicted v_a values. At 25deg;C, the progel's power law consistency coefficient (K) and v_a increased with increasing gelatin content and/or decreasing soy isolate content while the power law index (n) decreased. The reverse occurred when measurements were made at 40, 60 and 80deg;C. Soft gels formed when the progels were aged for 24 h at 4deg;C. Texture profile analysis and electron micrographs of the gels further emphasized the role of individual components in structural integrity and molecular interactions.     

BEHAVIOR OF MOZZARELLA, CHEDDAR AND PROCESSED CHEESE SPREAD IN LUBRICATED AND BONDED UNIAXIAL COMPRESSION

The response of a material under uniaxial compression depends both on the bulk material properties and on the frictional effects at the sample-platen interface. Three commercial cheeses (cheddar, mozzarella and processed cheese spread) were studied in uniaxial compression. Frictional effects at the sample surface were examined under three conditions: (1) lubrication of the sample-platen interface; (2) bonding of the sample to the instrument platens; (3) samples neither bonded nor lubricated. The forces required to deform the cylindrical sample to a given strain level were highest for the bonded cases and lowest under lubricated conditions. The stress in lubricated compression, ρ_L, was calculated from Fh(πR_ρ²h_ρ)     

低脂Mozzarella干酪品质的研究

通过设定不同脂肪含量,研究低脂Mozzarella干酪的蛋白水解、TPA质构、功能特性和微观结构.结果表明,低脂Mozzarella干酪的各个指标较全脂Mozzarella干酪均有所降低.其中,脱脂Mozzarella干酪的品质明显降低,接受性差;中脂Mozzarella干酪品质接近于全脂Mozzarella干酪,部分脱脂Mozzarella干酪介于脱脂和中脂Mozzarella干酪之间,具有可接受性.     

MEASURING ELONGATIONAL PROPERTIES OF MOZZARELLA CHEESE

A vertical uniaxial extension apparatus was developed for determining elongational properties of Mozzarella cheese over the course of one month of refrigerated storage. Cheese specimens suspended in hot oil (60C) first underwent melting and then stretching under the influence of a constant force. Samples did not break even after 400% extension. Strain rate and sample temperature both increased during a test. Transient elongational (TE) viscosity of Mozarella cheese decreased with increasing strain rate and sample temperature. Proteolysis of caseins in Moz-zarella, determined by gel electrophoresis, did not alter its TE viscosity to an extent measurable by our method.     

Mozzarella干酪拉伸机的设计

描述一种用于生产Mozzarella干酪的单螺杆拉伸机的设计,包括理论分析、机械设计以及试验论证.该拉伸机可以实现对凝乳颗粒的可控加热与拉伸,同时,为了直接获得直径20 mm～30mm的干酪块,在拉伸机出口处安装了小孔均匀分布的挤出板,使小尺寸的干酪块冷却时间缩短.该机试制的样品符合美国农业部关于Mozzarella干酪产品的标准.     

RHEOLOGICAL PROPERTIES OF MOZZARELLA CHEESE DETERMINED BY CREEP/RECOVERY TESTS: EFFECT OF SAMPLING DIRECTION, TEST TEMPERATURE AND RIPENING TIME

The viscoelastic properties of mozzarella cheese using a creep/recovery test considering different sampling directions (parallel and perpendicular to protein fiber orientation), test temperatures (20, 30 and 40C) and ripening times (1, 8, 15, 29 and 36 days) were studied. Creep data were interpreted by a Burger model of four parameters. A semiempirical approach was proposed to obtain the contribution of each main compliance to the total deformation of the system. Creep tests at different temperatures allowed gaining a better understanding of changes that occur in the cheese matrix during heating and ripening. Sampling direction did not affect any of the parameters studied. Finally, it was clearly observed that cheese matrix behaves as a quite different physicochemical system depending on temperature. Therefore, it is recommended to carry out the rheological tests at different temperatures to evaluate appropriately the viscoelastic properties of mozzarella cheese.

PRACTICAL APPLICATIONS

Mozzarella cheese must have certain characteristics to be used on pizzas and on other prepared foods that use the cheese in melted state. The protein chains in the mozzarella curds coalesce into large strands that are oriented in the direction of stretching. For this reason, mozzarella cheese has an anisotropic structure. Therefore, it is relevant to determine the effect of protein fiber orientation on the rheological properties. Valuable information may be obtained through the creep/recovery test of mozzarella cheese samples to study its rheological properties and to explain molecular mechanisms that occur during ripening or melting processes considering sampling direction.     

OBJECTIVE MEASUREMENT OF THE STRETCHABILITY OF MOZZARELLA CHEESE

Despite the great attention that has been devoted to cheese rheology to date no rheological analyses to characterize cheese stretchability by well-defined physical terms has been proposed. This paper illustrates the possibility of using a test commonly used to characterize polymer melt response to spinning to objectively measure cheese stretchability. The behaviour of cow milk Mozzarella cheese with varying temperature is presented. The results show that there exists a well-defined temperature range in which the cheese can be stretched, and that within this range there is a temperature at which the cheese stretchability reaches its maximum value.     

ASSESSMENT OF COHESION IN GRUYERE-TYPE CHEESE BY RHEOLOGICAL METHODS

The quantitative assessment of cohesion in unripened hard cheese was studied using static methods (uniaxial compression and tension, 3-point bending, and cutting) and transient methods (stress relaxation and creep). The two levels of cheese cohesion (denoted as weak and strong, according to the judgement of the cheesemaker) were obtained by two different manufacturing procedures. Statistical analysis showed that all static methods can be used to discriminate various levels of cohesion. Uniaxial tension proved to be the most powerful test to assess quantitatively the cohesive properties of hard cheese since the values of all parameters (fracture stress, fracture strain, work to fracture, modulus of deformability, and apparent flow modulus) depend significantly (α < 0.01) on the level of cohesion. Stress relaxation and creep tests were not as powerful as the rapid static methods in distinguishing the two levels of cheese cohesion.     

EVALUATION OF GOUDA CHEESE FIRMNESS BY COMPRESSION TESTS

Cheese maturity, test temperature, crosshead speed, sample shape, sample height and surface area influence the force-compression behaviour of Gouda cheese in an Instron Universal Testing Machine. Introducing mineral oil or Emery paper between the sample's surfaces and the compression plates affects the shape of the compressed samples. Cine-film records indicate that deformation is barrel-shaped (convex) with Emery paper and under normal test conditions, and concave with mineral oil. In the first two test situations friction prevents the cheese surfaces from spreading to the same extent during sample compression as when using mineral oil. Compression as modified by friction may be the principal factor associated with the subjective evaluation of firmness by squeezing samples between the fingers. Firmness evaluation by chewing involves still higher percent compressions which, in Instron tests, lead to sample breakdown and crack propagation.     

马苏里拉干酪(Mozzarella Cheese)的生产工艺探讨

介绍生产马苏里拉Mozzarella干酪的制作工艺,研究和探讨了最佳工艺参数,可为国内准备实现马苏里拉干酪工业化的生产单位提供参考。     

RHEOLOGICAL, MELTING AND MICROSTRUCTURAL PROPERTIES OF CHEDDAR AND MOZZARELLA CHEESES AFFECTED BY DIFFERENT FREEZING METHODS

Three cheeses were treated by (1) blast, (2) precooling plus blast, (3) liquid nitrogen and (4) precooling plus liquid nitrogen freezing methods. Mozzarella I and Cheddar cheeses treated by all methods had lower shear strength than their controls, excepting Mozzarella I treated by (1) was similar to its control. Mozzarella II treated by (1) and (2) had higher shear strength than its control but by (3) and (4) it had less. The failure stresses of Cheddar and Mozzarella I cheeses treated by (1) and (2) were significantly lower than their controls, while treated Mozzarella II had opposite results. Mozzarella I treated by (2) had meltability similar to its control and by (1) had lower meltability. Mozzarella II meltability was significantly reduced by (1) and (2). Stretchability was greatly improved using both methods for Mozzarella I but not for Mozzarella II. Cryo‐stage Scanning Electron Microscopy (SEM) showed that the microstructural differences caused by (1) and (2) were apparent in Cheddar and Mozzarella II but not in Mozzarella I.     

PREDICTION OF SENSORY TEXTURE OF FETA CHEESE MADE FROM ULTRAFILTERED MILK BY UNIAXIAL COMPRESSION AND SHEAR TESTING

The ability to predict sensory texture properties of Feta cheese made from ultrafiltered milk (UF-Feta) from uniaxial compression, small shear deformation measurements (frequency sweep, strain sweep, relaxation) and indices of proteolysis was studied. In principal component analysis (PCA) some of the instrumental variables were highly correlated, e.g. the moduli from uniaxial compression and shear measurements; and strain at fracture from uniaxial compression and indices of proteolysis. PCA of the six sensory attributes determined by a trained panel showed that mainly one type of information was present in the sensory results. Partial Least Squares regression (PLS) of all results revealed that stress at fracture from uniaxial compression was the individual instrumental parameter having the highest correlation with the sensory texture attributes. Of these, the three firmness attributes were best predicted by the instrumental parameters. As the shear measurements were not very useful for prediction of sensory texture properties by themselves, and as the increase in prediction precision by inclusion of these measurements was marginal, it is suggested that either stress at fracture alone, or together with three other parameters from uniaxial compression should be used to describe texture properties of UF-Feta cheese.