What makes mozzarella stretchy

The liquid whey is drained off and you are left with the curd at a pH of 5. The curd is heated in boiling weak brine and taken out intermittently and stretched. Following this the curd is moulded into shaped blocks or balls and packaged for consumption.

Variables that can affect the stretchability of Mozzarella include the type of milk, temperature, pH at various stages of the process; mechanical forces, e. The research group compares samples from different manufacturers and looks at the microstructure of different products.

The microstructure gives a good indication of the changes occurring in the cheese. This kind of microstructure is related to the stretching. This contrasts with Cheddar cheese that has a microstructure more reminiscent of a web, where the fat is more evenly dispersed. Anita has always liked dairy. She started out studying food technology and worked at various dairy companies before embarking on her PhD.

Anita benefits from access to the instruments such as the Electron Microscopes and other Advanced Microscopy facilities at the Bio21 Institute, which help her to investigate dairy microstructure.

Immediately after manufacturing, mozzarella cheese undergoes significant structural rearrangement, and the free water that occupies the interstitial area around the fat channels is absorbed into the protein matrix Certain techniques can be used to study the changes that occur during the mozzarella manufacturing, including nuclear magnetic resonance NMR , which have been shown to be powerful methods of evaluating changes in the structure and mobility of mozzarella cheese components 11 , 26 , In addition to NMR, confocal microscopy is a tool with great potential to improve the understanding of milk and cheese microstructure, including the size and shape of fat globules 28 , and it has been successfully used to study the three-dimensional network of fat and protein in both cheese and curd During storage, the composition of water and fat channels changes as the protein absorbs the free water formed during curd stretching within the channels These changes have been observed in studies that have evaluated the microstructure of mozzarella cheese 3 , 21 , Microstructural images captured during cheese maturation show a continuum of proteins containing intact fat and coalesced fat droplets.

These observations together with the decrease in serum extracted during ageing support the hypothesis that the increase in paracasein volume is due to an increase in hydration, probably as a result of proteolysis and solubilization of insoluble calcium The increase in water-binding capacity in the matrix is an important phenomenon because it affects the water-holding capacity and consequently the ability of the cheese to flow and stretch during heating The milk composition, its treatment, pH, acidity, calcium content, stretching conditions stretching water temperature, stirring speed, mechanical treatment and the type of stretching manual or mechanical are some of the factors that influence the stretching of mozzarella cheese.

Studies have shown that changes in processing conditions, such as the pH at whey drainage, interact with changes in composition e.

There are considerable individual changes in the concentrations of fat, protein, casein, lactose and minerals associated with seasonality. These changes, in turn, affect the gelation characteristics of the rennet and its cheese-making properties. In addition to composition, seasonality also affects the state quality of milk protein and fat and its standardization for cheese processing 14 , The chemical composition, and microbiological and enzymatic quality of milk have a major impact on the quality and consistency of the cheese.

Mozzarella is traditionally manufactured using raw milk The heat treatment of milk to process mozzarella cheese is a relatively new phenomenon due to the opening of big manufacturing industries of mozzarella cheese.

There are still several dairies that do not treat the milk with heat for mozzarella production. Pasteurization of milk has become a step in cheese making due to a number of countries and governmental agencies having restrictions on the use of raw milk Moreover, for mozzarella cheese that is to consumed fresh, pasteurization of milk is recommended because the stretching process does not always destroy pathogens According to Patel et al.

According to Rowney et al. Lowering the pH favours a change in the distribution of casein-associated calcium to the soluble state 2. This may be due to a higher level of calcium in the curd that has been stretched at a higher pH value 3.

The development of acidity during mozzarella cheese manufacturing should be controlled so that the correct combination of total calcium content, pH and moisture content in the curd are achieved during stretching 7.

Calcium plays an important role during mozzarella cheese processing because it helps with coagulation and promotes crosslinking between casein micelles When the serum is removed, insoluble calcium is retained after cutting the curd, while most of the soluble calcium is lost in the serum The lower solubilization of calcium in cheese than in milk occurs due to changes in calcium solubilization in the protein matrix, which has a higher solids concentration and higher ionic strength 9.

Studies have shown that there must be an optimal casein-associated calcium insoluble or colloidal calcium content, which is normally achieved through solubilization of this mineral by acidification, so that curd stretching occurs during mozzarella cheese production. Calcium solubilization during mozzarella processing occurs due to a reduction in pH 8 , Insoluble calcium is available to form crosslinks in the paracasein matrix when the curd is heated Two parameters determine the amount of casein-associated calcium during the stretching: i the total calcium content in the curd, and ii the distribution of total calcium between the soluble and colloidal forms 2.

As insoluble calcium content decreases, casein-casein interactions are fewer in number and weaker in strength, exhibiting a para -casein network with lower rigidity 8 and less thermal energy to obtain the gel-sol transition is needed Originally, mozzarella cheese was manually stretched 48 , and this process is still performed in small industries.

Mozzarella manufacturers use a wide range of industrial equipment for processing pasta filata cheese, including equipment with batch or continuous processes and single or double screw systems designed with different materials, geometries and heating systems, in which the process control parameters, such as the temperature, curd feed rate and screw speed, can be adjusted.

Consequently, thermomechanical treatments may differ considerably depending on the used equipment Mozzarella cheese can also be stretched using extruders, a method that is gaining significant commercial acceptance In this system, the plasticization gel-sol transition is influenced by the stretching temperature, residence time and curd composition, especially by the calcium content An advantage of the mechanical treatment is that individual curd particles are rapidly transformed into a heterogeneous but continuous flowable mass that can be easily moulded However, this treatment also causes a heterogeneous distribution of moisture in the mozzarella cheese 30 , and increased stirring speeds result in higher fat loss and lower moisture content With the objective of minimizing such problems, the development of systems for stretching mozzarella cheese without using water has been studied.

In this system, heating can be provided by direct steam injection, electromagnetic energy, heated auger bodies or a combination of these However, there is still a lack of studies dealing with equipment sizing or setting parameters based on the physical properties of cheese curd during the main stages of plasticization, conveying and texturization According to Fox et al.

If the stretching temperature is below the sol-gel transition temperature, which is also called the plasticizing temperature, the fibrous structure typical of the curd will not be obtained Regardless of the adopted type of stretching i.

Table 2 49 , 51 , 54 , 55 , 58 - 60 shows different stretching conditions employed in mozzarella cheese processing. The variations in temperature and pH depend on the conditions used in the mozzarella stretching and influence the cheese composition and thermophysical properties.

The curd stretching temperature influences the viability and activity of the starter bacteria in the final cheese. For this reason, a higher stretching temperature is sometimes desirable to increase the shelf life as it promotes greater thermal inactivation of microorganisms Yun et al. Depending on the extent of heat inactivation during stretching, the activity of the residual coagulant in low-moisture mozzarella cheese may also vary According to Yun et al.

The stretching temperature to which cheese is subjected influences the structure of cheese as it affects its components and their interactions, including changes in the physical state of fat and the molecular interactions between casein and fat 4. According to a study by Renda et al. At these temperatures, a corresponding increase in the strength of the hydrophobic interactions occurs within the protein matrix as the curd temperature increases, and this strengthening of the hydrophobic interactions results in the contraction of the protein matrix as the hydrophobic regions inside the protein get closer, which forces some of the water to change into a free state in the interstitial spaces around the fat globules According to Banville et al.

Smaller fat globules were observed in the cheese subjected to lower temperatures and lower stretching time, whereas larger fat globules and fat globule aggregation in the protein cavities in addition to the presence of free fat were observed in the cheese subjected to more severe stretching conditions. These results showed that the amount of mechanical energy supplied was directly proportional to the fat loss in the cheese and the amount of free whey was related to the thermal treatment intensity.

The authors concluded that thermomechanical systems impacted the cheese composition, loss of solids and microstructure. The stretching process is a heat treatment that profoundly affects the cheese composition and proteolysis during mozzarella storage. According to a study by Mulvaney et al. Rowney et al. Excessive and limited oil release are both considered defects 16 because they influence the appearance, taste and texture of mozzarella cheese when subjected to heating.

Traditionally mozzarella requires a maturation period between 7 and 21 days to develop optimal organoleptic and baking qualities During this period the distribution between casein-associated calcium insoluble calcium and soluble calcium is crucial for the functionality of mozzarella cheese 66 , A study by Joshi et al.

A partial solubilization of insoluble calcium during the first stage of maturation likely occurs due to a pseudobalance between the soluble and insoluble forms of calcium in the cheese The solubilization of insoluble calcium during mozzarella cheese storage has been previously reported 66 - 68 , and these changes are known to be of paramount importance for the hydration of the paracasein matrix and lead to changes in cheese texture during the first 10 days of storage Therefore, several strategies have been adopted for altering the calcium balance during cheese production.

In milk, changes in the fraction of insoluble calcium in total calcium have been made through preacidification, the addition of calcium chelating agents and acidification control. In cheese, the calcium content can be altered by modifying the process conditions Cheese with high total calcium content has a lower melting capacity than the cheese with a low total calcium content according to Lucey and Fox The concentration of total calcium in the cheese is one of the main factors that contribute to its melting because most of the calcium in the cheese is in an insoluble form that is capable of crosslinking with casein, involving phosphoserine groups These crosslinks help reinforce the entire protein network, thereby promoting greater stiffness and when heated, the melting of the cheese decreased 46 , A decrease in calcium mass fraction from 0.

Lucey and Fox 18 have suggested that insoluble calcium plays a much more significant role in determining the cheese textural properties than the total calcium content. According to Fathollahi et al. The insoluble calcium content plays an important role in the melting of skim mozzarella cheese.

Joshi et al. In another study, part-skim mozzarella cheese was obtained from the preacidification of milk, and cheese with a lower calcium content had a more homogeneous structure, a more hydrated protein matrix, a higher number of fat particles and higher emulsification, which resulted in increased melting of this cheese According to McMahon et al.

Table 3 18 , 21 , 31 , 44 , 46 , 52 , 55 , 69 , 72 , 73 summarises the processing variables and their impact on cheese functional properties. According to the discussed studies, the processing variables are not independent and have complex interactions.

If some aspect of the composition is changed, e. In addition, changes in processing conditions, for example lowering the pH, interact with changes in composition, for example calcium content, having a combined and complex effect on the functional properties of mozzarella cheese 7 , After the stretching stage, the hot curd is subjected to sufficient pre-cooling to maintain its shape when removed from the mould and immersed in cold brine.

Physicochemical changes of high-moisture mozzarella cheese during frozen storage and subsequent refrigerated storage after thawing were evaluated with NMR relaxometry and casein dehydration related to freezing was observable through changes in the water relaxation times within the matrix, which were confirmed by microstructural observations that showed the formation of larger serum channels surrounded by the protein matrix and formation of relatively bigger fat globule clusters in the samples submitted to freezing than in fresh cheese The formation of larger ice crystals during storage because of crystal growth and recrystallization can promote microstructural changes and the disruption of the casein matrix The cheese processed with a covering liquid had longer freezing times and showed water absorption phenomena during thawing.

Freezing may also be effectively applied to control or extend the functional shelf-life of low-moisture part-skim mozzarella cheese shipped to long-distance markets Proteolysis occurs through the action of residual enzymes present in cheese that hydrolyze casein, causing a breakdown in the protein matrix. However, the heating that occurs during stretching reduces the activity of the residual rennet in the curd, which reduces the extent of primary proteolysis during the storage of the mozzarella cheese Proteolytic changes in mozzarella curd influence melting, stretching and fat leakage characteristics Stretching is a key step for determining the cheese characteristics after manufacturing and during storage.

However, a few studies have separately evaluated the factors influencing the stretching process or stretching temperature by focusing on the reactions involved in the stretching step as well as the impact of these reactions on the functional properties of mozzarella throughout the refrigerated storage. A wide range of stretching water pH 4. Stretching under higher temperatures promotes more protein interactions, influences the viability and activity of the starter bacteria in the cheese, composition, yield, melting, water mobility, proteolysis and globule size, which may impact the release of oil in the cheese.

Throughout the storage period, the fraction of calcium is changed, and these changes influence the water mobility in the protein matrix. As the bacteria multiply, the whey liquid and curd solid milk proteins separate out.

This is a result of the pH, or acidity, dropping due to the bacterial metabolites. On a microstructural level, this is a jumble of protein and fat," Anita said. The liquid whey is drained off leaving the curd at a pH of 5.

Curd is then heated in boiling salty brine and taken out intermittently and stretched. Following this, the curd is moulded into shaped blocks or balls and packaged for consumption. Variables that can affect the stretchability of mozzarella include the type of milk, temperature, pH conditions for the lactic acid bacteria e.

The research group compares samples from different manufacturers and looks at the microstructure of the different products. The microstructure gives a good indication of the changes occurring in the cheese. In mozzarella the protein strands are lined up.

This kind of microstructure is related to the stretching. This contrasts with cheddar cheese that has a microstructure more reminiscent of a web, where the fat is more evenly dispersed. Anita has a scientific approach to her work and benefits from the access to the instruments such as Electron Microscopes and optical microscopes to investigate the dairy microstructure.

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