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.     

The compositional and functional properties of commercial mozzarella, cheddar and analogue pizza cheeses

The compositional and functional properties of commercial retail and/or wholesale samples (n = 8) of low-moisture mozzarella, cheddar and analogue (pizza) cheeses were compared. Inter-and intravariety differences were evident with intravariety differences in composition being relatively large for the analogue cheese. Cheddar had the lowest mean pH and level of expressible serum and the highest mean levels of proteolysis, expressible fat, and serum calcium and nitrogen (p < 0.05). Compared to mozzarella, the analogue cheeses had significantly lower (p < 0.05) mean levels of total protein and serum calcium, higher levels of total calcium and higher cheese pH. The mean stretchability of the melted mozzarella cheese was significantly higher than that of the melted cheddar or analogue cheeses. The melted cheddar had the highest mean flowability and lowest mean apparent viscosity (p < 0.05). The mean flowability and apparent viscosity of the analogue cheese were numerically lower and higher, respectively, than those of mozzarella.     

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.     

Evaluation of oxidative damage in mozzarella cheese produced from bovine or water buffalo milk

Technological processes are the main sources of protein and lipid oxidation in food. The oxidative status was determined in a soft Italian cheese, namely mozzarella, produced from water buffalo or bovine milk. The amount of protein-bound carbonyls, dityrosine and α-lactalbumin aggregates were measured to evaluate the extent of protein oxidation. The α-tocopherylquinone/α-tocopherol ratio and the trolox-equivalent antioxidant capacity were used as redox markers in the fat fraction. The levels of protein-bound carbonyls and α-lactalbumin aggregates were found significantly higher in bovine mozzarella than in buffalo mozzarella. On the other hand, higher amounts of redox markers were found in buffalo mozzarella. The levels of dityrosine aggregates were similar in the two types of cheese. The data suggest that protein and fat are more protected against oxidative structure alterations in buffalo mozzarella than in bovine mozzarella.     

Test for measuring the stretchability of melted cheese

A test for measuring the stretchability of cheese was developed by adapting a texture-profile analyzer to pull strands of cheese upwards from a reservoir of melted cheese. Seven different cheeses were analyzed using the Utah State University stretch test. The cheeses were also analyzed for apparent viscosity with a helical viscometer, for meltability using a tube melt test, and for stretch using the pizza-fork test. Cheese was placed into a stainless steel cup and tempered in a water bath at 60, 70, 80, or 90 degrees C for 30 min before analysis. The cup was then placed in a water-jacketed holder mounted on the base of the instrument. A three-pronged hook-shaped probe was lowered into the melted cheese and then pulled vertically until all cheese strands broke or 30 cm was reached. This produced a stretch profile as the probe was lifted through the reservoir of melted cheese and then pulled strands of cheese upwards. Three parameters were defined to characterize the stretchability of the cheese. The maximum load, obtained as the probe was lifted through the cheese, was defined as melt strength (F(M)). The distance to which cheese strands were lifted was defined as stretch length (SL). The load exerted on the probe as the strands of cheese were being stretched was defined as stretch quality (SQ). There was a correlation between F(M) and apparent viscosity. There was also some correlation between SL measured by the fork test and SL when the cheese was tested at 90 degrees C, but no correlation occurred at lower temperatures.     

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.     

莫扎雷拉干酪的工艺介绍

探讨制作莫扎雷拉干酪的制作工艺及拉伸工艺中的影响因素。经过试验,发现要获得优良的拉延特性,干酪凝块的最佳pH应控制在5.2~5.4,产品的钙/非脂乳固体比例约为3.1%±0.1%,水分含量为55%±2%,无脂干酪的水分含量为70%±3%,残糖含量按半乳糖计为7 g/kg,无乳糖残留。     

Improvement of low fat mozzarella cheese properties using denatured whey protein

Mozzarella cheese was made from buffalo milk (6% fat) or from partially skimmed buffalo milk (2 and 4% fat) with 0.5 and 1% denatured whey protein. Adding whey protein to buffalo milk decreased rennet coagulation time and curd tension whereas increased curd synaeresis. Addition of whey protein to cheese milk increased the acidity, total solids, ash, salt, salt in moisture, also some nitrogen fractions. The meltability and oiling‐off values increased but the calcium values of mozzarella cheese decreased. The sensory properties of low fat mozzarella cheese were improved by addition of whey protein to the cheese milk.     

Galactose concentration in pizza cheese prepared by three different culture techniques

A study was conducted to determine the most suitable lactic culture combinations and the techniques for the preparation of low moisture part skim (LMPS) mozzarella cheese (pizza cheese) with a low level of galactose. The cheesemaking time tested for all 12 culture combinations was less than 3 h and hence was found suitable for pizza cheesemaking. The initial accumulated galactose concentration was lower in unstretched curd followed by no-brine curd and stretched curd in ascending order. During storage of the cheese for 7 days, the galactose percentage in the cheeses prepared using cultures comprising galactose-fermenting strains of Lactobacillus helveticus and Streptococcus thermophilus was 0.30 in stretched curd, 0.04 in unstretched curd and 0.03 in no-brine curd. The degree of reduction in the level of galactose in pizza cheese during storage was maximum with the no-brine curd technique followed by the unstretched and stretched curd techniques in that order. This study provides information regarding selection of starter culture combinations and techniques for pizza cheesemaking based on consumer preference for low or moderate browning mozzarella cheese as a result of its galactose concentration.     

Composition,microstructure and chemical interactions during the production stages of Mozzarella cheese

Changes in chemical composition, microstructure and chemical interactions before and after the stretching stage of mozzarella cheese processing were investigated. The increased acidity and the decreased pH resulted in the solubilisation of total calcium. The protein matrix became more compact and the size of the fat globules decreased with the incorporation of small individual fat globules, aggregates and fat globules of irregular form into the matrix. The predominant bonds in the curd before the stretching stage were hydrophobic interactions, whereas the number of calcium bonds was minimal. After the stretching stage, the primary bonds responsible for maintaining the cheese structure were calcium bridges, electrostatic interactions and hydrogen bridges. These results clarify important aspects of the bonds involved in the production of this type of cheese.     

Correlating mozzarella cheese properties to its production processes and microstructure quantification

Production processes influence both the composition and microstructure of cheese. Frequently the relationship between property, processing and structure has been studied empirically and the complex interactions between all parameters have not been quantified. This is often due to the limited number of production processes used to produce samples which may potentially produce biased correlations. In this study mozzarella cheeses were manufactured with a range of compositions and production processes to give three groups of cheeses with different fat contents, draining pH or calcium contents, and stretching conditions, i.e. stretching temperature and speed. Principal Component Analysis was applied to the analysis of correlations within each group of cheese samples. In this study, we found that a positive correlation exists between the diameter of fat globules and meltability, as well as free oil. In addition, we also found a positive correlation between the protein content and stretching parameters.     

剪切条件下制备的肉糜中脂肪微粒的微观结构特点

研究在剪切条件下制备的肉糜中脂肪微粒分布规律及微观结构特点。以猪背最长肌为原料,绞碎斩拌3min后再加入背膘斩拌5min。分别用光学显微镜和电子显微镜对肉糜和凝胶进行电镜观察。结果表明：在剪切过程中,背膘被剪切成大小形状各不相同的液态脂肪滴和固态脂肪颗粒,有的脂肪滴和脂肪颗粒能够聚集形成脂肪微粒簇。其表面都包被着一层蛋白膜,或单独地或相互交联分散在蛋白基质中。     

Sarcomere length determination using front-face fluorescence polarization

Tryptophan is the major intrinsic fluorophore in muscle and is a constituent of proteins that have two preferential alignments both parallel and perpendicular to muscle fibre direction. A simple theoretical model and an experimental method based on front-face fluorescence polarization technique for tryptophan fluorescence anisotropy measurements were used for the estimation of post-rigor sarcomere length in beef in the range 1.6-3.4μm. Fluorescence anisotropy and structure-related model variables displayed changes in cold-shortened samples compared with normal and stretched ones. The anisotropy of contracted samples was lowered by misalignment of fibres in the sample. This method can therefore be used for in-line detection of cold shortening which has meat toughness as a consequence.     

The role of homogenization in the manufacture of halloumi and mozzarella cheese from recombined milk*

When halloumi and mozzarella cheese are made from normal recombined milk, neither product exhibits the characteristic stretch and melt behaviour of the fresh milk cheeses. The present study demonstrates that this problem may be overcome either by using low homogenization pressures to prepare the recombined milk or by coating the fat in the recombined milk emulsion with phospholipid and homogenizing at the usual pressure. The influence of homogenization of milk on the properties of the cheese is discussed in terms of a polymer network model.     

An approach to improve the baking properties and determine the onset of browning in fat-free mozzarella cheese

Compared with low-moisture part-skim mozzarella and mozzarella cheese, bake performance of low-fat and fat-free mozzarella on pizza has a lot to desire. We hypothesized that a water-soaking pretreatment step of low-fat and fat-free cheese shreds before baking would improve pizza baking performance. The study also examined the correlation of the onset of cheese browning with the rate of moisture loss, changes in cheese surface temperature, and 3-dimensional (3D) plot L* a* b* CIELAB color analysis. The pretreatment of soaking cheese shreds in water improved the baking properties of fat-free mozzarella cheese on pizza. Compared with the control sample, which demonstrated significant shred identity, poor shred melt, fusion, and stretch during a pizza bake with fat-free mozzarella, the soaked cheese (SC) sample demonstrated satisfactory cheese melt, fusion, and stretch. In addition, the SC sample had desired browning as opposed to the control sample's excessive browning. The additional moisture from the soaking pretreatment aided in delaying the onset of cheese browning in the SC sample when compared with the control sample. For both the control and SC samples, there was a strong correlation between the onset of cheese browning with the peak of moisture-loss rate, and an increase in cheese surface temperature (>100°C). The color analysis of the 3D plot confirmed the relationship between the onset of cheese browning and the shift in L* (lightness), a* (red-green color), and b* (blue-yellow) values. According to the study's findings, soaking cheese shreds before baking can help improve bake performance on pizza. Furthermore, 3 measurement tools used in the study, (1) moisture-loss rate, (2) cheese surface temperature, and (3) 3D plot CIELAB color, were useful in determining the onset of cheese browning and can be applied to different intervention strategies to control cheese browning during pizza baking.     

Environmental life cycle assessment of Italian mozzarella cheese: Hotspots and improvement opportunities

The present study investigated a cradle-to-grave life cycle assessment to estimate the environmental impacts associated with Italian mozzarella cheese consumption. The differences between mozzarella produced from raw milk and mozzarella produced from curd were studied, and differences in manufacturing processes have been emphasized in order to provide guidance for targeted improvements at this phase. Specifically, the third-largest Italian mozzarella producer was surveyed to collect site-specific manufacturing data. The Ecoinvent v3.2 database was used for secondary data, whereas SimaPro 8.1 was the modeling software. The inventory included inputs from farm activities to end of life disposal of wasted mozzarella and packaging. Additionally, plant-specific information was used to assign major inputs, such as electricity, natural gas, packaging, and chemicals to specific products; however, where disaggregated information was not provided, milk solids allocation was applied. Notably, loss of milk solids was accounted during the manufacture, moreover mozzarella waste and transport were considered during distribution, retail, and consumption phases. Feed production and animal emissions were the main drivers of raw milk production. Electricity and natural gas usage, packaging (cardboard and plastic), transport, wastewater treatment, and refrigerant loss affected the emissions from a farm gate-to-dairy plant gate perspective. Post-dairy plant gate effects were mainly determined by electricity usage for storage of mozzarella, transport of mozzarella, and waste treatment. The average emissions were 6.66 kg of CO₂ equivalents and 45.1 MJ of cumulative energy demand/kg of consumed mozzarella produced directly from raw milk, whereas mozzarella from purchased curd had larger emissions than mozzarella from raw milk due to added transport of curd from specialty manufacturing plants, as well as electricity usage from additional processes at the mozzarella plant that are required to process the curd into mozzarella. Normalization points to ecotoxicity as the impact category most significantly influenced by mozzarella consumption. From a farm gate-to-grave perspective, ecotoxicity and freshwater and marine eutrophication are the first and second largest contributors of mozzarella consumption to average European effects, respectively. To increase environmental sustainability, an improvement of efficiency for energy and packaging usage and transport activities is recommended in the post-farm gate mozzarella supply chain.     

Deformation of collagenous, elastin and muscle fibres in raw meat in relation to anisotropy and length ratio

The influence of strain directions on the mechanical properties of raw meat samples in a compression test was analysed in relation to the contracted or stretched state and discussed in terms of connective network deformation. When the lateral deformation of a sample is in the direction of muscle fibres, the more the meat has been stretched ante-rigor, the smaller the strain range in which muscle fibres can be solicited alone and the lower the critical compression ratio at which collagenous fibres come under tension. Post-rigor contraction occurring in stretched muscles modifies the relations between muscle fibres and collagenous fibres and increases the critical compression ratio. The greatest post-rigor contractions have been observed in stretched slices of Semitendinosus and Lattissimus dorsi which are high elastin content muscles. This suggests that elastin has a major role in post-rigor contraction. In greatly contracted post-rigor samples, as muscle fibres are wavy, they are not involved at low strains, likewise collagenous fibres around muscle fibres cannot be stressed until the waviness of muscle fibres has been removed. Therefore, in greatly contracted post-rigor samples, the mechanical properties observed at low strains might belong mainly to elastin fibres. When the lateral deformation is perpendicular to the direction of muscle fibres these fibres are not involved and the more the meat has been stretched ante-rigor the higher the critical compression ratio.     

Investigation of stretch on air permeability of knitted fabrics part II: effect of fabric structure

The structure of a fabric plays vital role in determining its air permeability. So, the study and comparison of air permeability of various fabric structures have their own significance. A detailed study is carried out here on various fabric structures to understand the effect of fabric structure on air permeability at their dry, wet and fully relaxed states. An automatic fabric stretching device has been designed and fabricated as an attachment with air permeability tester to test the air permeability of fabric samples under dynamic condition for this investigation. It is a fully automatic stretching equipment to stretch the fabric samples as per the preset value. The stretching device can be set with a predetermined degree of fabric stretch either in percentage or in mm and rate of extension also can be preset in mm per minute. From the results, it is clear that fabric structure has explicit impact on air permeability both in the unstretched and stretched states of the samples. Loose fabric structure and porous fabric structure show maximum air permeability under both sedate state and incrementally stretched states and vice versa.     

Characterization of high pressure jet–induced fat-protein complexation

High-pressure-jet (HPJ) processing of various dairy systems has been shown to disrupt fat droplets and casein micelles and cause a strong association between fat and casein proteins. The present work seeks to better describe this association between fat and casein using a model milk formulated from confectionary coating fat (3.6% wt/wt), micellar casein (3.4% wt/wt), and water (93% wt/wt), which was then pasteurized, homogenized, and then either HPJ-treated (400 MPa) or not (non-HPJ-treated, control). Upon ultracentrifugation, fat in the non-HPJ-treated model milk creamed due to its low density. In the HPJ-treated model milk, fat precipitated with protein into a thick bottom layer upon ultracentrifugation, reflecting a strong association between protein and fat. Differential scanning calorimetry (DSC) and time-domain nuclear magnetic resonance of the non-HPJ-treated model milk revealed fat in 2 physical states: (1) fat that is physically similar to the bulk fat and (2) fat that was in smaller droplets (i.e., homogenized) and crystallized at a lower temperature than the bulk fat. In contrast, DSC of HPJ-treated model milks supported the presence of fat in 3 states: (1) fat that is physically similar to the bulk fat, (2) fat in small droplets that required substantial supercooling beyond the non-HPJ-treated model milk to crystallize, and (3) fat in such small domains that it crystallizes in a less stable polymorphic form than the non-HPJ-treated model milk (or does not crystallize at all). The state of fat within the HPJ-treated model milk changed minimally with acidification, indicating that the association is not dependent on the charge on the casein. Cryogenic transmission electron microscopy (Cryo-TEM) of the non-HPJ-treated model milk revealed uniform casein micelles, which likely adsorbed to the surface of fat globules post-homogenization. In contrast, Cryo-TEM of the HPJ-treated model milk revealed a porous protein aggregate that likely had dispersed fat throughout. Together, these results suggest that HPJ treatment causes fat to be entrapped by casein proteins in very small domains.     

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.