Correlating mozzarella cheese properties to production processes by rheological,mechanical and microstructure study: Meltability study and Activation energy

Meltability is one of the most important properties of mozzarella cheese as it is generally used melted, and neither too high nor too low meltability can be accepted by consumers. However, there is no widely accepted objective method to evaluate cheese meltability. The most commonly used method, the Schreiber test, cannot be used as a standard evaluation method because of its varying test conditions. Another method based on the temperature sweep of Small Amplitude Oscillatory Shear analysis (SAOS) is rarely used for meltability evaluation. The aim of this study is therefore to study the Schreiber test and to develop the method of SAOS to evaluate cheese meltability. Based on SAOS, an Arrhenius plot is obtained from a temperature sweep and the activation energy (Ea) is calculated from the Arrhenius plot within the temperature range of 30 °C to 45 °C. This study compares these two methods on eleven mozzarella cheese samples with different stretching conditions, pH, fat or calcium content. It is found that the meltability of mozzarella cheese produced with different stretching conditions has no significant difference; high fat and low fat samples have the highest and lowest meltability respectively; and samples with low draining pH have similar meltability with the ones with low calcium content, and vice versa.     

Changes in the rheological properties of Iranian UF-Feta cheese during ripening

The frequency sweep test was used to evaluate storage modulus (G′), loss modulus (G′′) and loss tangent [tan (δ)] of Iranian UF-Feta cheese during ripening period (3, 20, 40 and 60 days). With development of ripening, storage and loss moduli increased at varying rates. The rate of increase in G′ was greater than that in G′′ resulting in a reduction in tan (δ). That is, storage modulus was dominant to loss modulus and as a result the elasticity nature was greater than the viscous nature of cheese samples. Due to the disruption of fat globules and proteolysis, protein matrix rearranged and formed a more compact texture containing aggregates of casein. Ripening did not influence the pH level and also the concentrations of dry matter, fat, salt, and total nitrogen in dry matter. However, water soluble nitrogen increased significantly (P < 0.05).     

Camembert干酪凝乳过程中微观结构与流变特性的变化

利用流变仪和激光共聚焦扫描显微镜追踪和观察牛乳凝乳的形成过程,通过研究经不同条件处理的Camembert干酪在凝乳时的流变特性和微观结构的变化,来探讨TG酶和CaCl2对干酪品质的影响机制.随着TG酶添加量的增大,凝块聚集交联在一起,凝乳聚集胶团更小,并形成较致密的网络结构;而添加CaCl2引入Ca2+,可显著缩短凝乳时间,提高凝乳凝胶强度.     

Insoluble calcium content and rheological properties of Colby cheese during ripening

Colby cheese was made using different manufacturing conditions (i.e., varying the lactose content of milk and pH values at critical steps in the cheesemaking process) to alter the extent of acid development and the insoluble and total Ca contents of cheese. Milk was concentrated by reverse osmosis (RO) to increase the lactose content. Extent of acid development was modified by using high (HPM) and low (LPM) pH values at coagulant addition, whey drainage, and curd milling. Total Ca content was determined by atomic absorption spectroscopy, and the insoluble (INSOL) Ca content of cheese was measured by the cheese juice method. The rheological and melting properties of cheese were measured by small amplitude oscillatory rheometry and UW-Melt Profiler, respectively. There was very little change in pH during ripening even in cheese made from milk with high lactose content. The initial (d 1) cheese pH was in the range of 4.9 to 5.1. The INSOL Ca content of cheese decreased during the first 4 wk of ripening. Cheeses made with the LPM had lower INSOL Ca content during ripening compared with cheese made with HPM. There was an increase in melt and maximum loss tangent values during ripening except for LPM cheeses made with RO-concentrated milk, as this cheese had pH <4.9 and exhibited limited melt. Curd washing reduced the levels of lactic acid produced during ripening and resulted in significantly higher INSOL Ca content. The use of curd washing for cheeses made from high lactose milk prevented a large pH decrease during ripening; high rennet and draining pH values also retained more buffering constituents (i.e., INSOL Ca phosphate), which helped prevent a large pH decrease.     

Phase structures impact the rheological properties of rennet-casein-based imitation cheese containing starch

The dynamic rheological and microstructural properties of rennet-casein-based imitation cheeses containing various concentrations of potato starch were investigated using a stress-controlled rheometer and confocal laser scanning microscopy. The influence of added starch on the size of the oil droplets in the imitation cheeses was also examined. Imitation cheeses with 0–15% protein replaced by starch were processed in a Rapid Visco Analyser (RVA) at 90 °C for 10 min at a shear rate of 800 rev/min and were then evaluated using oscillatory shear measurement and a temperature sweep (20–90 °C). The storage modulus (G′) of the rennet casein imitation cheeses increased abruptly at added starch concentrations >4%. In the temperature range 20–90 °C, tan δ of the imitation cheeses decreased with increasing starch concentration and was <1 at added starch concentrations >4%. A binary continuous phase consisting of a protein phase and a starch phase was observed in systems containing >4% starch, whereas the starch was dispersed in the protein matrix as small particles of irregular shapes at added starch concentrations ≤4%. As the dispersed phase, the size of the oil droplets increased with starch addition in the imitation cheeses. The marked increase in G′ and the reduction in tan δ may be attributed to the formation of a binary continuous separated phase structure in imitation cheeses containing added starch that is driven by thermodynamic incompatibility between rennet casein and starch.     

Microstructure and rheological properties of Iranian white cheese coagulated at various temperatures

The effect of milk coagulation temperature on the composition, microstructure monitored using scanning electron micrographs, opacity measured by a Hunter lab system, and rheological behavior measured by uniaxial compression and small amplitude oscillatory shear were studied. Three treatments of Iranian White cheese were made by applying coagulation temperatures of 34, 37, and 41.5°C during the cheese-making procedure. A higher coagulation temperature resulted in increased fat and protein contents, and decreased the moisture content and ratio of moisture to protein. The highest temperature (41.5°C) had a significant effect on the opacity of Iranian White cheese. Milk coagulation at this temperature decreased the whiteness index (Hunter L value) and increased the yellowness index (Hunter b value) of the aged product compared with cheeses coagulated at lower temperatures. Microstructure of the cheese coagulated at 41.5°C was more compact and undisturbed, reflecting the higher values of stress at fracture and storage modulus measured for this treatment.     

The influence of moisture content on the rheological properties of processed cheese spreads

Model processed cheese spreads were prepared from rennet casein, sunflower oil, water and a trisodium citrate/citric acid chelating salt system. The samples were cooked using a laboratory‐scale processed cheese cooker. The moisture content of the samples varied from 49.1 to 55.6%. The samples were characterized by dynamic rheology, rotational viscometry and fat particle size analysis. With increasing moisture content, the rheological behaviour of the samples changed from solid‐like (concentrated solution) to liquid‐like (dilute solution). The moduli decreased and the frequencies at which G′‐G′′ crossed over increased with increasing moisture content. Increasing moisture content resulted in an increase in pH and increase in the volume‐to‐surface diameter of the fat droplets. Rotational viscometry indicated that all the samples were shear thinning. The flow curves fitted a power law relationship (r² = 0.993). Thixotropic behaviour was displayed by all samples except those above 54% moisture. The shear stress at any particular shear rate increased with decreasing moisture content, indicating a stronger network structure in the low moisture samples.     

Effect of selected Hofmeister salts on textural and rheological properties of nonfat cheese

Three Hofmeister salts (HS; sodium sulfate, sodium thiocyanate, and sodium chloride) were evaluated for their effect on the textural and rheological properties of nonfat cheese. Nonfat cheese, made by direct acidification, were sliced into discs (diameter = 50 mm, thickness = 2 mm) and incubated with agitation (6 h at 22°C) in 50 mL of a synthetic Cheddar cheese aqueous phase buffer (pH 5.4). The 3 HS were added at 5 concentrations (0.1, 0.25, 0.5, 0.75, and 1.0 M) to the buffer. Post-incubation, cheese slices were air dried and equilibrated in air-tight bags for 18 h at 5°C before analysis. Small amplitude oscillatory rheology properties, including the dynamic moduli and loss tangent, were measured during heating from 5 to 85°C. Hardness was determined by texture profile analysis. Acid-base buffering was performed to observe changes in the indigenous insoluble (colloidal) calcium phosphate (CCP). Moisture content decreased with increasing HS concentration. Cheeses incubated in high concentrations of SCN⁻ softened earlier (i.e., loss tangent = 1) compared with other HS treatments. Higher melting temperature values were observed for cheeses incubated in high concentrations of SO₄²⁻. Hardness decreased in cheeses incubated in buffers with high concentrations of SCN⁻. The indigenous CCP profile of nonfat cheese was not greatly affected by incubation in Cl⁻ or SCN⁻, whereas buffers with high concentrations of SO₄²⁻ reduced the acid-base buffering contributed by CCP. The use of high concentrations (1.0 M) of SCN⁻ for incubation of cheeses resulted in a softer protein matrix at high temperatures due to the chaotropic effect of SCN⁻, which weakened hydrophobic interactions between CN. Cheese samples incubated in 1.0 M SO₄²⁻ buffers exhibited a stiffer protein matrix at high temperatures due to the kosmotropic effect of SO₄²⁻, which helped to strengthen hydrophobic interactions in the proteins during the heating step. This study showed that HS influenced the texture and rheology of nonfat cheese probably by altering the strength of hydrophobic interactions between CN.     

Effect of chitosan on the rheological and sensorial characteristics of Apulia spreadable cheese

The effect of chitosan on the rheological and sensorial properties of Apulia spreadable cheese during storage time was evaluated. The investigated spreadable cheese samples were stored at 4°C. Storage modulus (G′), loss modulus (G″), tanδ, and the overall sensorial quality of the spreadable cheese were monitored for 24 d. Moreover, moisture content, pH, color, and lactic acid bacteria during storage time were evaluated. Results indicate that statistically significant differences in G′, G″, and tanδ values and in the sensorial scores exist between the control sample and the spreadable cheese samples with chitosan. In particular, chitosan improved the rheological and sensorial properties of the spreadable cheese, particularly its softness. Moreover, its addition influenced the physicochemical properties of the investigated spreadable cheese during storage time, without affecting the dairy microflora.     

Effect of freezing on the rheological, chemical and colour properties of Serpa cheese

The effect of freezing on the properties of a raw ewes'-milk semi-soft cheese (Serpa cheese) was studied using small amplitude oscillatory (SAOS) and texture measurements, colour and chemical parameters. The freezing was introduced at three different stages of the ripening process (28, 35 and 42 days), and the cheeses were maintained frozen for 12 months. Cheeses were submitted to a slow or fast freezing method, and to different storage temperatures: -10 and -20°C (three replicates for each set conditions). Chemical data showed that only the proteolysis indicators exhibited differences between frozen and non-frozen samples; frozen samples showed higher values of NPN than the non-frozen samples, indicating that the freezing process did not prevent the secondary proteolysis of cheese. Frozen samples showed a significantly (P<0·05) stronger structure than the non-frozen, as indicated by hardness. However, the differences between the frozen and non-frozen samples were not significantly for storage modulus (G' 1Hz) and loss tangent (tan δ 1Hz) (P>0·05). Freezing affected mainly colour parameters: frozen samples were more luminous, and more yellow-green. The results allowed us to conclude that the damages caused by freezing to cheese properties could be minimized if this type of storage is introduced at the end of ripening (42 d) using a freezing temperature of -20°C.     

Composition,structure, rheological properties,and sensory texture of processed cheese analogues

Processed cheese analogues were made with different fat and moisture in nonfat solids (MNFS) contents and used to study relationships between composition, microscopic structure, rheological properties and sensory texture. Fat contents ranged from 58 to 230 g kg^?1 and MNFS from 487.6 to 603.3 g kg^?1. Regressions showed that those rheological parameters measured by uniaxial compression at large deformations and moderately high rates were best explained by linear combinations of MNFS, protein and fat. The moisture in the protein network acted as a plasticiser lowering the rheological parameters. Fat alone had little direct effect on the rheological characteristics under these conditions but at small deformations and low deformation rates it formed elastic inclusions that contributed to the properties. Examination of fracture surfaces in the SEM suggested that, during fracture, fat was squeezed out and acted as a lubricant. Maximum stress and work to maximum stress measured at moderately high deformation rates related best to the sensory results and described fracture of the cheeses. From the regressions, for 95% confidence limits, sensory analysis could theoretically measure changes within the range of composition tested of <0.1% in MNFS or fat. Of the rheological parameters only work to maximum stress was as sensitive. However, interaction between these compositional factors reduced the sensitivity in practice.     

Influence of lamb rennet paste containing probiotic on proteolysis and rheological properties of pecorino cheese

Pecorino cheeses made from heat-treated ewes’ milk using traditional lamb rennet paste (RP), lamb rennet paste containing Lactobacillus acidophilus (LA-5; RPL), and lamb rennet paste containing a mix of Bifidobacterium lactis (BB-12) and Bifidobacterium longum (BB-46; RPB) were characterized for proteolytic and rheological features during ripening. Consumer acceptance of cheeses at 60 d of ripening was evaluated. Lactobacillus acidophilus and Bifidobacterium mix displayed counts of 8 log₁₀ cfu/g and 9 log₁₀ cfu/g, respectively, in cheese during ripening. The RPB cheese displayed a greater degradation of casein (CN) matrix carried out by the enzymes associated to both Bifidobacterium mix and endogenous lactic acid microflora, resulting in the highest values of non-CN N and water-soluble N and the highest amount of α_s-CN degradation products in cheese at 60 d of ripening. The RPL cheese displayed intermediate levels of lactic acid bacteria and of N fractions. The percentage of γ-CN in RP and RPL cheeses at 60 d was 2-fold higher than in the cheese curd of the same groups, whereas the mentioned parameter was 3-fold higher in RPB cheese than in the corresponding fresh curd according to its highest plasmin content. The lower hardness in RPB at the end of ripening could be ascribed to the greater proteolysis observed in cheese harboring the Bifidobacterium mix. Although differences in proteolytic patterns were found among treatments, there were no differences in smell and taste scores.     

Effect of frozen storage on the proteolytic and rheological properties of soft caprine milk cheese

Freezing and long-term frozen storage had minimal impact on the rheology and proteolysis of soft cheese made from caprine milk. Plain soft cheeses were obtained from a grade A goat dairy in Georgia and received 4 storage treatments: fresh refrigerated control (C), aged at 4°C for 28 d; frozen control (FC), stored at −20°C for 2 d before being thawed and aged in the same way as C cheese; and 3-mo frozen (3MF), or 6-mo frozen (6MF), stored at −20°C for 3 or 6 mo before being thawed and aged. Soft cheeses had fragile textures that showed minimal change after freezing or over 28 d of aging at 4°C. The only exceptions were the FC cheeses, which, after frozen storage and aging for 1 d at 4°C, were significantly softer than the other cheeses, and less chewy than the other frozen cheeses. Moreover, after 28 d of aging at 4°C, the FC cheeses tended to have the lowest viscoelastic values. Slight variation was noted in protein distribution among the storage treatment, although no significant proteolysis occurred during refrigerated aging. The creation and removal of ice crystals in the cheese matrix and the limited proteolysis of the caseins showed only slight impact on cheese texture, suggesting that frozen storage of soft cheeses may be possible for year-round supply with minimal loss of textural quality.     

Effect of protective atmospheres on physicochemical,microbiological and rheological characteristics of sliced Mozzarella cheese

Mozzarella cheese slices packaged in bags of polyvinylidene chloride under vacuum (V) and using a gas mixture of equal parts of CO₂ and N₂ (G) were stored at 4 °C for 8 weeks and analysed at different storage times by physicochemical, microbiological and rheological characterization. Expected values of moisture, total nitrogen, soluble nitrogen at pH 4.6, and chloride contents and of pH were observed. The degradation of α_s1-casein was greater than β-casein degradation, while no significant differences were observed due to the packaging methods. Coliform microorganisms were not detected, while levels of moulds and yeasts counts were acceptable. Expected values of total mesophile counts were obtained. The temperature at crossover moduli (T_c) was determined from temperature sweeps carried out by rheometry. Greater values of T_c were observed in samples G. The influence of temperature on complex viscosity was studied by an Arrhenius-type equation. Activation energy values were obtained from the solid-like region (20–40 °C) and liquid-like region (40–60 °C). A more rapid change in viscosity with temperature was observed when storage time increased and when storage method V was used.     

Impact of modifications in acid development on the insoluble calcium content and rheological properties of Cheddar cheese

Cheddar cheese was made from milk concentrated by reverse osmosis (RO) to increase the lactose content or from whole milk. Manufacturing parameters (pH at coagulant addition, whey drainage, and milling) were altered to produce cheeses with different total Ca contents and low pH values (i.e., <5.0) during ripening. The concentration of insoluble (INSOL) Ca in cheese was measured by cheese juice method, buffering by acid-base titration, rheological properties by small amplitude oscillatory rheometry, and melting properties by UW-Melt Profiler. The INSOL Ca content as a percentage of total Ca in all cheeses rapidly decreased during the first week of aging but surprisingly did not decrease below approximately 41% even in cheeses with a very low pH (e.g., ∼4.7). Insoluble Ca content in cheese was positively correlated (r = 0.79) with cheese pH in both RO and nonRO treatments, reflecting the key role of pH and acid development in altering the extent of solubilization of INSOL Ca. The INSOL Ca content in cheese was positively correlated with the maximum loss tangent value from the rheology test and the degree of flow from the UW-Melt Profiler. When cheeses with pH <5.0 where heated in the rheometer the loss tangent values remained low (<0.5), which coincided with limited meltability of Cheddar cheeses. We believe that this lack of meltability was due to the dominant effects of reduced electrostatic repulsion between casein particles at low pH values (<5.0).     

Effect of denatured whey protein concentrate and its fractions on cheese composition and rheological properties

The objectives of this study were (1) to assess the effect of a denatured whey protein concentrate (DWPC) and its fractions on cheese yield, composition, and rheological properties, and (2) to separate the direct effect of the DWPC or its fractions on cheese rheological properties from the effect of a concomitant increase in cheese moisture. Semihard cheeses were produced at a laboratory scale, and mechanical properties were characterized by dynamic rheometry. Centrifugation was used to induce a moisture gradient in cheese to separate the direct contribution of the DWPC from the contribution of moisture to cheese mechanical properties. Cheese yield increased and complex modulus (G*) decreased when the DWPC was substituted for milk proteins in milk. For cheeses with the same moisture content, the substitution of denatured whey proteins for milk proteins had no direct effect on rheological parameters. The DWPC was fractionated to evaluate the contribution of its different components (sedimentable aggregates, soluble component, and diffusible component) to cheese yield, composition, and rheological properties. The sedimentable aggregates were primarily responsible for the increase in cheese yield when DWPC was added. Overall, moisture content explained to a large extent the variation in cheese rheological properties depending on the DWPC fraction. However, when the effect of moisture was removed, the addition of the DWPC sedimentable fraction to milk increased cheese complex modulus. Whey protein aggregates were hypothesized to act as active fillers that physically interact with the casein matrix and confer rigidity after pressing.     

Yield, composition and rheological characteristics of cheddar cheese made with high pressure processed milk

High Pressure (HP) treatment of milk prior to cheese-making was shown to increase the yield of cheese due to increased protein and moisture retention in cheese. Cheeses were made with raw milk or milk treated with high temperature short-time (HTST) pasteurization, and HP treatments at two levels (483 and 676 MPa) at 10 °C, 483 MPa HP at 30 °C, and 483 MPa HP at 40 °C. Cheese yield, total solids, protein, fat and salt contents were evaluated, and fat and protein recovery indices were calculated. Cheeses from HP treatments of 676 MPa at 10 °C and 483 MPa at 30 °C exhibited wet yields of 11.40% and 11.54%, respectively. Protein recovery was 79.9% for HP treatment of 676 MPa at 10 °C. The use of slightly higher pressurization temperatures increased moisture retention in cheese. Visco-elasticity of cheeses was determined by dynamic oscillatory testing and a creep-recovery test. Rheological parameters such as loss (G″) and storage (G′) moduli were dependent on oscillation frequency. At high (173 rad/s) and low (2.75 rad/s) angular frequencies, cheeses made from milk treated at 483 MPa at 10 °C behaved more solid-like than other treatments. Creep tests indicated that cheeses from milk treated with 483 MPa HP at 10 °C showed the smallest instantaneous compliance (J_o), confirming the more solid-like behavior of cheese from the 483 MPa at 10 °C treatment compared to the behavior of cheeses from other treatments. Cheeses made with pasteurized milk were more deformable, exhibited less solid-like behavior than cheeses made with HP treated milk, as shown by the J_o value. With more research into bacteriological implications, HP treatment of raw milk can augment Cheddar cheese yield with better curd formation properties.     

Changes in rheological and viscoelastic properties and protein breakdown during the ripening of 'Port Salut Argentino' cheese

Changes in the rheological behaviour and viscoelastic properties during ripening at 10°C of a soft cheese (Port Salut Argentino) packaged in a plastic film (EVA-EVA) were analysed. Casein degradation was measured by electrophoresis slab gels; α_s1 casein degradation was rapid and striking compared with that of β casein. Rheological parameters obtained from uniaxial compression tests changed during ripening: hardness decreased, adhesiveness and cohesiveness increased.
An exponential decay equation with two maxwellian elements and one elastic in parallel was fitted to characterize stress relaxation curves. Viscoelastic parameters (elastic moduli and relaxation times) were obtained using non-linear regression analysis. The elastic equilibrium modulus decreased 80% during the ripening period and the viscosity of the element with the highest relaxation time decreased 20%. These parameters represented the changes observed in cheese hardness and elasticity during ageing time and were related to the extent of casein breakdown.