Cheese, also known as cheese, is made by fermenting fresh milk and is a fermented dairy product. During the fermentation of milk, under the action of enzymes and microorganisms, proteins are gradually degraded into small molecules such as peptides and amino acids, which make them easier to digest. In addition, cheese is rich in nutrients and is known as “milk gold”.

Cheese

According to GB 5420-2010 National Standard for Food Safety Cheese, cheese is a ripened or unripened soft, semi-hard, hard or extra-hard dairy product that may be coated, and in which the ratio of whey protein/casein does not exceed the corresponding ratio in milk.

1.1 Cheese is obtained by the following methods:

(a) It is obtained by coagulating or partially coagulating the proteins of one or more of the raw materials in milk, skimmed milk, partially skimmed milk, thin cream, whey thin cream, buttermilk, in the presence of rennet or other suitable rennetting agent, discharging a portion of the whey from the curd. This process is a concentration of milk proteins (especially the casein fraction), i.e. the protein content of the cheese is significantly higher than the protein content of the raw materials used;

(b) A process which involves the coagulation of the proteins in milk and/or milk products and which confers on the finished product physical, chemical and organoleptic properties similar to those of the product described in (a).

1.2 Cheese is divided into ripened cheese, mold-ripened cheese and unripened cheese:

(1) Matured cheese ripened cheese

After production can not be immediately used (food), should be stored at a certain temperature for a certain period of time, in order to produce the characteristics of the type of cheese through biochemical and physical changes in the cheese.

(2) Mold ripened cheese mould ripened cheese

Cheese which is ripened mainly by the growth of characteristic molds on the interior and/or surface of the cheese.

(3) Unripened cheese

Unripened cheese (including fresh cheese) is cheese which is ready for use shortly after production.

Refined cheese

According to the provisions of GB 25192-2010 National Standard for Food Safety Refined Cheese. Refined cheese process(ed) cheese is made from cheese (proportion greater than 15%) as the main raw material, adding emulsifying salt, adding or not adding other raw materials, made by heating, stirring, emulsifying and other processes.

Difference between processed cheese and re-manufactured cheese

3.1 Nutritional content

Generally speaking, the nutritional content of cheese is higher than that of reconstituted cheese. The graph below shows data on the indicators of three natural Mozzarell cheeses and three reconstituted Mozzarell cheeses:

The protein mass fraction was significantly higher in the natural cheeses than in the reconstituted cheeses, the moisture mass fraction was significantly lower than in the reconstituted cheeses, and the pH value was significantly lower than in the reconstituted cheeses; the fat mass fraction in the natural cheeses and the reconstituted cheeses differed depending on the brand of cheese.

3.2 Differences in texture

Due to the addition of emulsifying salt, the solubility of casein is improved and a thin layer is formed on the surface of the fat. The fat globules with a thin layer of protein on the surface can be stabilized and not separated during the heating process, so the reconstituted cheeses can maintain a homogeneous state and a soft texture.

3.3 Shelf life

Although natural hard cheese can be stored for a period of time, when the proteolytic and lipolytic activities in the curd are too frequent, the curd will eventually deteriorate. Refined cheese has relatively good stability due to the heat treatment process, which destroys most of the residual microorganisms and enzyme activity.

3.4 Physical and chemical properties

3.4.1 Hardness

It can be seen from the table that the hardness of natural cheese is significantly higher than that of prepared cheese; there is no significant difference in the elasticity of the two types of cheese: the cohesion of natural cheese is higher than that of prepared cheese. There is no significant pattern of change in the adhesion of natural cheeses and the restructured cheeses.

The hardness of the cheese was determined by the non-fatty dry matter in the cheese, which was mainly reflected in the spatial mesh structure constructed by the casein proteins. The higher protein mass fraction in natural cheese increases the degree of cross-linking between casein molecules, resulting in higher cohesion. In contrast, a higher fat mass fraction can be able to interrupt the cross-links between caseins to some extent, significantly reducing the cohesiveness of the cheese.

Any factor that affects the interaction of proteins with water or with other substances affects the adhesion of cheese. There are significant differences in the physicochemical properties of natural and reconstituted cheeses, and different processing conditions also affect the interaction of proteins with water or with other substances; therefore, there are differences in the viscosity of different cheeses, and there is no obvious pattern of change in the viscosity of the two types of cheeses.

3.4.2 Tensile strength

It can be seen from the figure that the stretchability of natural cheese is significantly higher than that of reconstituted cheese.

Stretchability is the ability of the casein mesh structure to remain unbroken after stretching, and is related to the interactions between the casein micelles in the cheese and factors such as moisture, calcium and fat content. The fraction of protein in natural cheese is higher than that in reconstituted cheese, and the casein intermolecular interactions are stronger and more resistant to stretching.

3.4.3 Meltability

The meltability of cheese is usually expressed in terms of the area of diffusion of the cheese at a given temperature; the larger the area of diffusion, the better the meltability of the cheese.

The meltability of cheese is related to the extent to which the protein system is destroyed by melting of the fat during heating, during which protein interactions are weakened, the protein system is moved and the cheese begins to flow. During processing of reconstituted cheese the fat globules in the cheese become smaller and more uniformly distributed in the casein mesh structure under the action of emulsifying salts and shear, and the ability of the fat to disrupt the casein mesh structure is reduced during the heating process, so that the melting properties of the reconstituted cheese deteriorate.

3.4.4 Grease precipitability

The fat precipitation of natural cheese is significantly higher than that of reconstituted cheese, and the occurrence of fat precipitation in cheese requires that the oil be released from the collapsed casein mesh, consolidated, and migrated to the surface of the cheese.

Therefore, the size and density of the fat globules, and the degree of incorporation of the fat into the casein mesh structure will have an effect on the fat separability of the cheese. As mentioned above, fat globules become smaller and more evenly distributed during the processing of reconstituted cheeses under the action of emulsifying salts, shear forces, etc., and the tendency of fat globules to merge during the heating process becomes smaller; therefore, the fat precipitation of reconstituted cheeses is significantly lower than that of natural cheeses.

The different processing techniques and composition of the raw materials are the main reasons for the differences in solubility and fat release between natural and reconstituted cheeses.

3.4.5 Modulus of elasticity, loss angle tangent

It can be seen from the figure that there is a significant difference in the trend of modulus of elasticity and loss angle tangent with temperature between natural cheese and reconstituted cheese.

Among them, the modulus of elasticity of natural cheese shows a decreasing trend with increasing temperature, and the loss angle tangent shows an increasing and then decreasing trend with increasing temperature, and the loss angle tangent reaches 1 at 50-60℃.

The modulus of elasticity of reconstituted cheese showed a tendency to decrease and then increase with temperature, and the loss angle tangent showed a tendency to increase and then decrease, but the loss angle tangent was always lower than 1 in the experimental temperature range.

Cheese is a viscoelastic object, in which the modulus of elasticity characterizes the solidity of the cheese mesh structure. the modulus of elasticity of natural cheese was higher than that of the reconstituted cheese at 20°C, which is consistent with the hardness results, suggesting that the casein mesh structure of natural cheese is more compact. During heating, the fat globules liquefied and deformed, the casein micelles contracted, and the bonds between the proteins were weakened, resulting in a decrease in the modulus of elasticity of the cheese.

As the temperature of the reconstituted cheese continued to increase, the modulus of elasticity tended to increase, probably due to the formation of additional forces between the proteins resulting in the strengthening of the cheese system.

The increase in loss angle tangent during heating indicates a phase transition of the cheese system from a more elastic system to a more viscous system. When the modulus of viscosity is greater than the modulus of elasticity, or the loss angle tangent exceeds 1, the cheese begins to melt. The larger the tangent of the angle of loss, the easier the bonds between proteins are broken and the easier the structural rearrangement occurs, which is reflected in the better melting and mobility of the cheese.

The low level of destruction of the protein mesh structure by fat during heating of the reconstituted cheeses is consistent with the results of the melting properties of the cheeses, and therefore the melting properties of the reconstituted cheeses are poorer than those of the natural cheeses, and the loss angle tangent never reaches 1.

In conclusion, there are significant differences in the physicochemical and functional properties of natural and reconstituted cheeses. Natural cheese is more suitable as an ingredient for foods that require baking such as pizza and risotto, while reconstituted cheese can be used as cheese slices in foods that do not require baking such as sandwiches.