Rheology of mozzarella cheese

The rheological properties of mozzarella cheese were studied by using a parallel plate, a sliding plate, an extensional and a capillary rheometer over a temperature range of 25–60 °C. While mozzarella cheese behaves as a semisolid at room temperature, it behaves mostly as a liquid at higher temperatures (typically greater than 40 °C). The rheological data obtained from the various pieces of rheometers were compared. Differences among the various data sets were observed and these were demonstrated to be due to the inherent changes to the material structure during testing and to the changes in the physical properties of the cheese at different temperatures. Mozzarella cheese is a viscoelastoplastic material at room temperature, which becomes viscoelastic at about 60 °C. Its yield stress gradually decreases with increase of temperature pointing to structural changes that occur at elevated temperatures. A Herchel–Buckley viscoplastic rheological model was found to describe adequately its rheology.     

Effect of Curd Washing Level on Proteolysis and Functionality of Low-Moisture Mozzarella Cheese Made with Galactose-Fermenting Culture

Abstract: The effect of curd washing on functional properties of low-moisture mozzarella cheese made with galactose-fermenting culture was investigated. A total of 4 curd washing levels (0%, 10%, 25%, 50% wt/wt) were used during low-moisture mozzarella cheese manufacture, and cheeses were stored for 63 d at 4 °C and the influence of curd washing on proteolysis and functionality of low-moisture mozzarella cheese were examined. Curd washing had a significant effect on moisture and ash contents. In general, moisture contents increased and ash contents decreased with increased curd washing levels. Low-moisture mozzarella cheese made with 10% curd washing levels showed higher proteolysis, meltability, and stretchability during storage than other experimental cheeses. In general, galactose contents decreased during storage; however, cheeses made with 25% and 50% curd washing levels had lower galactose contents than those with control or 10%. L*-values (browning) decreased and proteolysis increased in low-moisture mozzarella cheeses during storage.     

Rheology of mozzarella cheese: Extrusion and rolling

A capillary rheometer was used to determine the processability and rheology of mozzarella cheese over the temperature range of 25–60 °C. End pressure corrections, which are corrections associated with the entry and exit of the mozzarella cheese in and out of the capillary die, were found to be significant. Surprisingly, wall slip was found to be insignificant up to shear stress values of 30 kPa. Capillary extrusion at low temperatures (<50 °C) resulted in extrudates that were distorted, while at higher temperatures (>50 °C), the extrudates were fairly smooth. Rolling experiments at 25 °C indicated that rolling can be used to shape mozzarella cheese (at a reduction ratio <2.1) without fracturing. Based on the extrusion and rolling experiments, mozzarella cheese can be described as a power law fluid with an index of about 0.24, while at higher temperatures (30 °C<T<60 °C), the power law index is about 0.4, indicating its increased flowability.     

A dual‐acidification process for the manufacture of direct‐acidified Cottage cheese

A technology is described for manufacturing Cottage cheese which involved initial cold (4 °C) acidification of milk with HCl to bring down the pH to 5.3 followed by tempering slowly to 15 °C and subsequent acidification through slow hydrolysis of glucono delta lactone, resulting in a drop in pH to 5.0 and thereafter renneting at 20 °C followed by setting and cutting of curd and subsequent cooking at 35 °C for ~30 min. The method enabled manufacturing of Cottage cheese curd with average moisture, curd yield and curd hardness being 74.30%, 11.88% and 648.30 mN, respectively.     

Influence of the frozen storage period on the coagulation properties of caprine milk

Coagulation properties of caprine milk frozen for up to 60 days at −27 °C were investigated using a rheometer with a vane geometry tool. Coagulation time (CT) and aggregation rate (AR) were estimated during gel formation for 64 min at 1 Hz and 1% strain. Evaluation of curd firmness (CF) was done using frequency spectra of the resulting gels. The data were processed by ANOVA and linear regression (with frozen storage time as independent variable and pH, AR, CT and CF as dependent variables). No statistically significant changes in coagulation properties were found, although the milk pH decreased from 6.64 (non-frozen pasteurised milk) to 6.41 after 60 days of frozen storage. The results of this research showed that the coagulation properties of caprine milk were not significantly altered during 60 days frozen storage. It could be assumed, therefore, that the cheese-making processing properties of caprine milk would also not change.     

Systematic approach to study temperature and time effects on yield of pasta filata cheese

A batch cooker‐stretcher for pasta filata cheese production was developed based on the kitchen machine ‘Thermomix’. With this batch model system, the effect of kneading time (180, 420 and 600 s) and temperature (55, 60 and 70 °C) on the chemical composition of the pasta filata cheese and the yield was investigated. An increase in temperature from 55 to 70 °C reduced the yield of the pasta filata cheese production from 0.88 to 0.59 g/g, compared to initial curd weight. A correlation between process temperature and the water‐holding properties of protein (casein micelles) is proposed.     

Non-invasive monitoring of curd syneresis upon renneting of raw and heat-treated cow's and goat's milk

Molecular mobility of water during curd syneresis was investigated in raw and heat-treated cow's and goat's whole milk by Time-Domain ¹H Nuclear Magnetic Resonance (TD-NMR). Rennet was added to raw and heat-treated (72 °C) milk inside the NMR magnet at 40 °C, and curd evolution was monitored non-invasively over time. Distributions of ¹H NMR spin–spin relaxation time constants (T₂) were obtained at time zero (just after rennet addition), after 30 min (complete curd coagulation) and during serum expulsion (syneresis), every 10 min up to 70 min. Relaxation times and abundances of detected ¹H populations were calculated at each time point. Although further statistical validation would require a larger sample number, raw and heat-treated milk and the corresponding curd samples showed different NMR behaviour. It can be concluded that TD-NMR is able to identify differences between the molecular dynamics characterising raw milk and curd, and their heat-treated counterparts.     

Rheological Properties of Mozzarella Cheese Filled with Dairy, Egg, Soy Proteins, and Gelatin

The Rheological behavior of mozzarella cheese filled with various proteins (whey protein, caseinate, egg white, soy protein isolate, gelatin) incorporated was determined by uniaxial compression at 10°C and the effect of temperature (10°C?60°C) by dynamic measurement. Mozzarella cheese with whey protein, caseinate, egg white, and soy protein isolate showed significant water retention during heating. Among the proteins, soy protein isolate induced the strongest gel network structure with mozzarella cheese. All proteins altered the viscoelastic properties of mozzarella cheese.     

Microbiological,chemical, textural and sensory characteristics of Hispánico cheese manufactured using frozen ovine milk curds scalded at different temperatures

Hispánico cheese is a semi-hard variety, manufactured in Spain from a mixture of pasteurized bovine and ovine milk. To study one strategy for overcoming a seasonal shortage of ovine milk in summer and autumn, curds made from ovine milk, scalded at 32, 35 or 38 °C, were pressed for 30 min and frozen at ?24 °C for 4 months. After thawing, they were added to fresh bovine milk curd for the manufacture of experimental Hispánico cheeses. Control cheese was made from a mixture of pasteurized bovine and ovine milk in the same (80:20) proportion. No significant effect of the addition of frozen ovine milk curd or scalding temperature was found for lactic acid bacteria counts, dry matter content, hydrophilic and hydrophobic peptides, 45 out of 65 volatile compounds, texture, and sensory characteristics throughout a 60-day ripening period. Differences between cheeses, of low magnitude and little practical significance, were found for pH value, aminopeptidase activity, proteolysis, free amino acids, free fatty acids, and the remaining 20 volatile compounds. Thus, the addition of frozen ovine milk curd to fresh bovine milk curd does not alter the main physicochemical and sensory characteristics of Hispánico cheese.     

A new method for producing superior set yogurt,focusing on heat treatment and homogenization

Extended shelf life (ESL) processing (i.e., heat treatment at 130°C for 2 s) is usually not used for producing set yogurt because of the fragility of the curd structure. We investigated the effects of homogenization conducted at higher pressure than the conventional conditions (10 MPa for the first stage and 5 MPa for the second stage) on the curd structure of set yogurt, with a focus on the fat globule size. Each yogurt mix was adjusted at the range of fat globule sizes from 0.45 μm to 1.1 μm by a homogenizer and then heated at 95°C for 5 min (conventional heat treatment), 120°C for 2 s, ESL processing, or 140°C for 2 s. The yogurt mixes were fermented by a common yogurt starter, and the curd texture of the obtained yogurts was evaluated. We observed that the curd hardness and curd firmness of the yogurt were each negatively correlated with the fat globule size regardless of the heat-treatment temperature. Compared with the curd obtained with conventional heat treatment, the ESL-processed curd was extremely fragile, but significantly smooth. With ESL processing, a curd hardness >40 g, which is a sufficient strength for commercial transport systems, was obtained by making the fat particle size <0.6 µm, using 2-stage homogenization pressure: 35 MPa for the first stage and 5 MPa for the second stage. A microscopy analysis indicated that the smaller fat globules reinforce the network structure. The yogurt made by ESL processing and that created with 35 + 5 MPa homogenization had significant sensory evaluation scores. Our results indicate that the combination of ESL processing and 35 + 5 MPa homogenization is a novel and useful method for manufacturing set yogurt.     

Rheological Analysis of Sucrose Solution at High Temperatures Using a Microwave‐Heated Pressurized Capillary Rheometer

Thermal process design, optimization, and deviation require the knowledge of engineering properties of food, such as rheological behavior, which is highly dependent on temperature. If a process is calculated based on the parameters obtained by extrapolation, it might lead to over‐ or underprocessing. The long time required for the product to reach the desired temperature, which is usual in many rheometers, may induce unexpected changes on the product. Model solutions are often used in engineering projects in order to simulate characteristics of real products. Thus, the objective of this study was to obtain rheological data of sucrose model solution at the actual high UHT (ultra‐high temperature) process temperatures using a pressurized capillary rheometer, heated by a microwave system. The results provide the rheological behavior of the sucrose solutions and show that there is no deviation of the linearity of the Arrhenius plot above 100 °C for this product. This work was useful to illustrate the use of the applied methodology and to validate the newly built microwave‐heated capillary rheometer. The data obtained confirm the stability of nonsaturated sucrose solution when treated above 100 °C and presents an important contribution to the literature database, since sucrose solutions are used as models for many table syrups, such as maple and sorghum syrups.     

Influence of mixing temperature on xanthan conformation and interaction of xanthan–guar gum in dilute aqueous solutions

Dynamic viscoelastic and intrinsic viscosity properties of xanthan, guar, and xanthan–guar blends in dilute aqueous solutions were investigated by using an oscillating capillary rheometer. Influence of mixing temperature on xanthan conformation and interaction with guar is discussed. Synergistic interaction occurred at mixing temperatures of 25 and 80 °C, but a stronger synergistic interaction was observed at mixing temperature 80 °C. The viscous component for all gum solutions was greater than that of the elastic component, which indicated a liquid-like behavior in the dilute regime for the polysaccharide solutions. For both mixing temperatures, the relative viscosities and elasticities of xanthan and guar blends were higher than the relative viscosities and elasticities calculated for blends assuming no interaction. The intrinsic viscosities of xanthan and xanthan–guar blends were higher at 80 °C than at 25 °C. The intrinsic viscosities of xanthan and guar blends were lower than those calculated from the weight averages of the two, and significantly decreased as the xanthan fraction decreased, indicating that xanthan was crucial in controlling the blend viscosity, and that the molecular binding occurred between xanthan and guar.     

Tensile testing to quantitate the anisotropy and strain hardening of mozzarella cheese

We explored anisotropy of mozzarella cheese: its presence is debated in the literature. Tensile testing proved a good method because the location and mode of failure were clear. Mozzarella cheese cut direct from the block showed no significant anisotropy, though confocal microscopy showed good structure alignment at a microscale. Deliberately elongated mozzarella cheese showed strong anisotropy with tensile strength in the elongation or fibre direction ∼3.5× that perpendicular to the fibres. Temperature of elongation had a marked impact on anisotropy with maximum anisotropy after elongation at 70 °C. We suggest the disagreement on anisotropy in the literature is related to the method of packing the mozzarella cheese into a block after the stretching stage of manufacture. Tensile stress/strain curves in the fibre direction showed marked strain hardening with modulus just before fracture ∼2.1× that of the initial sample, but no strain hardening was found perpendicular to the fibre direction.     

Influence of lactic starter inoculation,curd heating and ripening temperature on Staphylococcus aureus behaviour in Manchego cheese

Growth and survival of Staphylococcus aureus were investigated in 52 lots of raw ewe's milk Manchego cheese manufactured and ripened under different conditions. A 5.8-fold reduction in S. aureus counts after 60 days of ripening was obtained by inoculating milk with 1% Streptococcus lactis culture, and a further 2.0-fold reduction could be achieved by adding 0.1% Lactobacillus plantarum culture. Curd heating temperature had a significant effect on S. aureus survival, with counts 4–5 times lower in cheese from 30° C curd than in cheese from curd heated at 36–40° C. Ripening temperature was the parameter with the greatest influence on S. aureus counts, which reached in cheese cured at 10° C or 20° C for 60 days levels 10 and 100 times lower, respectively, than in cheese held at 5° C.     

Effect of Air-Drying Conditions on Physico-chemical Properties of Osmotically Pre-treated Pomegranate Seeds

The drying of pomegranate seeds was investigated at 40 °C, 50 °C and 60 °C with air velocity of 2 m/s. Prior to drying, seeds were osmodehydrated in 55 °Brix sucrose solution for 20 min at 50 °C. The drying kinetics and the effects of osmotic dehydration (OD) and air-drying temperature on antioxidant capacity, total phenolics, colour and texture were determined. Analysis of variance revealed that OD and air-drying temperature have a significant influence on the quality of seeds. Both anthocyanin and total phenolic contents decreased when air-drying temperature increased. The radical diphenylpicril-hydrazyl activity showed the lowest antioxidant activity at 60 °C. Both chromatic parameters (L*, C* and h°) and browning index were affected by drying temperatures, which contributed to the discolouring of seeds. The final product has 22%, 20% and 16% of moisture; 0.630, 0.478 and 0.414 of a _w; 151, 141 and 134 mg gallic acid equivalent/100 g fresh matter (FM) of total phenolics; 40, 24, 20 mg/100 g FM of anthocyanins and 46%, 39% and 31% of antioxidant activity, for drying temperatures of 40 °C, 50 °C and 60 °C, respectively. In view of these results, the temperature of 40 °C is recommended as it has the lowest impact on the quality parameters of the seeds. Differential scanning calorimetry data provided complementary information on the mobility changes of water during drying. Glass transition temperature (Tg′) depends on moisture content and as consequence, on drying conditions. In fact, Tg′ of seeds dried at 60 °C (Tg′ = −21 °C) was higher than those dried at 50 °C (Tg′ = −28 °C) or 40 °C (Tg′ = −31 °C) and osmodehydrated seeds (Tg′ = −34 °C). During OD and drying process, the texture of seeds changed. The thickness of seeds shrank by 55% at 60 °C.     

Biocontrol of Staphylococcus aureus in curd manufacturing processes using bacteriophages

The ability of specific bacteriophages to inhibit Staphylococcus aureus growth in curd manufacturing processes was determined. Two lytic bacteriophages specific against S. aureus were obtained by DNA random deletion from the milk-isolated temperate phages, ΦH5 and ΦA72. A cocktail of these lytic phages, Φ88 and Φ35, at multiplicity of infection (MOI) of 100, produced a complete elimination of 3×10⁶ cfu mL⁻¹ of the pathogen in ultra-high-temperature (UHT) whole milk at 37 °C. Furthermore, the frequency of emergence of bacteriophage-insensitive mutants was reduced up to 200-fold in the presence of the two lytic phages compared with that detected with the combination of the temperate counterparts. The lytic phage derivatives, added to milk, were able to decrease rapidly the viable counts of S. aureus during curd manufacture. In acid curd, the pathogen was not detected after 4 h of incubation at 25 °C, whereas pathogen clearance was achieved within 1 h of incubation at 30 °C in renneted curd. These results indicate that lytic bacteriophages could be used as biopreservatives in the manufacture of particular dairy products.     

Parameters affecting the printability of 3D-printed processed cheese

In considering three-dimensional (3D) printing of food materials, fundamental understanding of the “printability” characteristics of different food materials is of vital importance to successfully meet user needs. In this study, a processed cheese formulation was 3D-printed with a modified 3D printer. Both intrinsic factors (i.e., pH and intact casein content) and measureable attributes (i.e., texture, printing accuracy, rheology and microstructure) were analysed. Using rheological methods, the optimal viscosity range (7.55–10.94 Pa.s) at which processed cheese will print successfully (i.e., simultaneously flow from the extrusion head uninhibited and build a layered structure) was identified. Processed cheese with a higher pH (5.8) was found to give a printed product that was significantly (P < 0.05) softer, gummier and more resilient in texture than the same recipe with a lower pH (5.4 and 5.6). Printed cheese containing exclusively fresh curd was significantly (P < 0.05) harder than that containing mild or mature Cheddar cheese. 3D printing at higher temperatures (60 °C) led to harder and more resilient cheese than printing at lower temperatures (40 °C). Overall, formulation and printing parameters for processed cheese significantly affect properties relating to “printability”.     

Microstructure and rheological properties of whipped cream as affected by heat treatment and addition of stabilizer

Whipping cream, 36% fat, was processed at 75°C for 16 s (high-temperature short time, HTST), and 140°C for 4 s, (ultra-high temperature, UHT) with and without added stabilizer. Following heat treatment and chilling for 24 h (5°C), cream samples were whipped to maximum overrun. Structural properties were assessed through low-temperature scanning electron microscopy (LTSEM) and dynamic oscillatory testing, using a controlled stress rheometer, immediately after the cream was whipped, and again after the foam was stored for 24 h at 5°C. No differences between fresh foam treatments were observed. However, aged foams exhibited changes in microstructure because of destabilization of the foam. Differences between aged foams resulted from the addition of stabilizers and the choice of heat treatment. Microstructural differences correlated well with measured changes in rheological properties.     

Multi-frequency power thermosonication treatments of clear strawberry juice: Impact on color,bioactive compounds,flavor volatiles,microbial and polyphenol oxidase inactivation

Strawberry juice is popular among consumers for its bright color, unique flavor and rich nutrition. The aim of this study was to explore the suitable multi-frequency power thermosonication (TS) treatments to meet the requirements of microbiological safety for strawberry juice while maximizing the preservation of its quality properties. The TS treatments included 60 °C /5 min and 55 °C /15 min under dual-frequency concentrated ultrasound (DCU) and 60 °C /15 min and 55 °C /20 min under sweep-frequency divergent ultrasound (SDU). The results showed that all treatments could meet the requirements of commercial sterility (at 90 °C for 1 min). Compared with thermal processing (TP) at 90 °C for 1 min, TS treatment significantly improved the color properties of strawberry juice. SDU-60 °C and SDU-55 °C greatly retained the active ingredients in the strawberry juice. TS treatments had a stronger ability to maintain the aroma compared to TP. Especially, SDU-60 °C was the best treatment at retaining quality properties of strawberry juice with the highest comprehensive sensory evaluation score (7.68). Therefore, the results can provide scientific basis for industrial production of strawberry juice.Industrial relevanceIn the current study, results showed that TS maximized the overall quality of strawberry juice while achieving the effect of sterilization and enzyme inactivation. Among them, SDU-60 °C was the best treatment method to maintain the quality characteristics of strawberry juice, which can effectively reduce the loss of approximately 70% of total phenolic content. Thus, it provides the theoretical basis and technical support for the industrial production of strawberry juice.     

Cheese made from instant infusion pasteurized milk: Rennet coagulation,cheese composition,texture and ripening

Milk subjected to instant infusion pasteurization (IIP) at 72 °C, 100 °C and 120 °C (holding time 0.2 s) exhibited increased rennet coagulation time and decreased curd firming rate for increasing heat treatment temperature, when compared with raw or high temperature short time pasteurized (HTST) milk. However, addition of 4.5 mm or 9.0 mm of calcium restored the impaired rennet coagulation ability. Open texture cheeses produced from IIP milk (100 °C and 120 °C) contained significantly more moisture, had lower pH and shorter texture than similar cheese from IIP at 72 °C and HTST pasteurized milk. Cheese ripening was also affected by heat treatment, and different patterns of casein breakdown and peptide formation resulted from cheeses made from milk treated to IIP at 100 °C and 120 °C compared with cheeses made using IIP at 72 °C or HTST.