METHOD FOR MAKING YOGURT OR ANOTHER FERMENTED MILK- BASED PRODUCT

Technical field

The present invention relates to a method for making yogurt or another fermented milk-based product. In particular, the invention proposed herein may be used in the dairy industry for producing yogurt, animal or vegetable cream (with fat content of up to 15%) and fermented milk.

Background art

As is known, the industrial production of yogurt starts with the "maintenance" step, during which the milk is heated, filtered to remove any impurities and cooled to a temperature of below 5°C. The maintenance step allows the lipid and protein characteristics of the milk to stabilise in order to measure them and guarantee correct preservation during the subsequent processing steps.

After the maintenance, the milk is pasteurised, i.e. subjected to a thermal treatment that aims to eliminate pathogenic microorganisms, promote the development of the microbial flora subsequently inoculated, make the curd more compact and reduce the phenomenon of the separation of whey.

For the production of set yogurt (i.e. full coagulation) the pasteurisation consists of maintaining the temperature at about 90°C for 5 minutes.

The pasteurisation is followed by the homogenisation wherein the particles of fat are broken up to contrast the formation of agglomerates and to uniform their dimensions. The homogenisation pressure is typically comprised between 200 and 250 bar.

To increase the compactness of the yogurt a "concentration" step may be envisaged, wherein the solid substance content of the milk is increased to 15% through evaporation, ultra-filtration and, often, powdered milk addition.

This is followed by the fermentation step, during which the temperature of the milk is brought up to about 40°C and a mixture of bacteria is inoculated, for example the colony of Steptococcus thermophilus and Lactobacillus bulgaricus in equal proportions. For example, the inoculation takes place in a simple tank.

In the production of set yogurt, i.e. with full coagulation, the inoculated milk must be transferred into the pots quickly, for example, 30 minutes - one hour at the most.

The inoculated bacteria multiply using lactose as a source of energy, therefore the concentration of the latter is reduced while lactic acid is produced in parallel, which is responsible for the lowering of the pH from 4 to 5, with consequent precipitation of casein and formation of curd.

The pots are kept in a warm chamber for an amount of time comprised between 3 and 6 hours, according to the inoculated mixture and the fermentation temperature set.

Alternatively, the transfer time can be increased by lowering the temperature to about 20°C, therefore the multiplication speed of the bacteria is reduced.

Once the curd has formed and the desired acidity has been reached, the pots are transferred into a blast chiller where they are cooled to below 18°C to stop the fermentation process.

Subsequently, the pots are moved into a refrigeration cell for further cooling to 4°C and for storage.

The addition of liquid flavourings takes place directly in the inoculation tank, whereas fruit or solid additives are dosed directly into the final containers.

The main drawback of the production cycle described above lies in the high energy expenditure of some steps. In particular, to reach high viscosity and good consistency of the final product the homogenisation pressure must be at least 200-250 bar. These are relatively high values which imply high energy consumption, as well as wear on components and reduction of the life span thereof.

Moreover, compounds are often added (such as enzymes or proteins) to the standard product which improve its rheology properties but imply an overall increase in the costs of the recipe.

Disclosure of the invention

In this context, the object of the present invention is to provide a method for making yogurt or another fermented milk-based product, which uses less energy than the known solutions.

In particular, the object of the present invention is to propose a method for making yogurt or another fermented milk-based product, which allows the viscosity and texture of the final product to be increased without increasing the cost of the recipe.

The technical task set and the objects specified are substantially attained by a method for making yogurt or another fermented milk-based product that comprises the following steps (which are not in chronological order):

- pasteurising the milk;

- adding to the milk an enzyme preparation based on transglutaminase at a concentration of 0.5-3 units per gram of proteins contained in the milk, the transglutaminase being supported on vegetable fibres;

- homogenising the pasteurised milk by forcing the milk through a gap afforded between a lower annular chamber and an upper annular chamber of a homogenising valve;

- subjecting the homogenised milk to fermentation.

For example, the addition of the enzyme preparation to the milk takes place before the step of pasteurising the milk, with transglutaminase at a concentration of 2-3 units per gram of proteins contained in the milk.

Alternatively, the addition of the enzyme preparation to the milk takes place after the step of pasteurising the milk, with transglutaminase at a concentration of 0.5-2 units per gram of proteins contained in the milk. Preferably, fermentation takes place by inoculating a predefined bacterial culture at a temperature comprised between 42°C and 44°C.

In the preferred embodiment, the vegetable fibres that support the transglutaminase enzyme are obtained from potato {Solanum tuberosum) and psyllium seeds {Plantago ovata).

Preferably, the vegetable fibres are in a weight percentage comprised between 5% and 10% of the enzyme preparation.

Preferably, the enzyme preparation comprises demineralized buttermilk. The enzyme preparation described above, in its preferred embodiment, is instantly soluble, a physical property obtained through a granulation production process wherein gum arabic is used as a processing aid.

Preferably, the homogenising valve comprises an annular passage head and an annular impact head interposed between the lower annular chamber and the upper annular chamber. The passage gap for the milk is defined between the passage head and the impact head.

Brief description of drawings

Further characteristics and advantages of the present invention will become more apparent from the following indicative, and hence non- limiting, description of a preferred, but not exclusive, embodiment of a method for making yogurt or another fermented milk-based product, wherein the homogenisation step is performed in a homogenising valve illustrated in figure 1 , in a sectional view.

Detailed description of preferred embodiments of the invention

In particular, the description proposed herein will refer to the production of yogurt. For example, the method can be used both for making set yogurt (i.e. full coagulation) and for making creamy yogurt. Furthermore, the method can also be used for making animal or vegetable cream or fermented milk.

The method comprises the steps of:

- pasteurising the milk;

- homogenising the pasteurised milk;

- subjecting the homogenised milk to fermentation.

In particular, the milk is pasteurised according to known techniques which are not the subject matter of the present invention.

The pasteurisation is followed by the homogenisation step, which is performed by forcing the milk through a gap afforded between a lower annular chamber 9 and an upper annular chamber 10 of a homogenising valve 1 .

In the preferred embodiment described and illustrated herein, the homogenising valve 1 comprises a valve body 2 defining a through hole with an axial extension with respect to the valve body 2.

Preferably, the valve body 2 is formed by the assembly of a lower valve body 3 and an upper valve body 4, which are axially aligned.

The valve 1 comprises a lower piston 5, inserted in a first section of the through hole at the lower valve body 3, and an upper piston 6, inserted in a second section of the through hole at the upper valve body 4. The lower piston 5 and the upper piston 6 are integrally coupled.

The valve 1 presents an inlet 7 for the fluid (in this case milk) at high pressure and an outlet 8 for the homogenised fluid at low pressure. The inlet 7 can be connected to a high pressure pump (not shown).

Between the valve body 2 and the lower piston 5, the lower annular chamber 9 is afforded, into which the inlet 7 for fluid at high pressure opens.

Between the valve body 2 and the upper piston 6, the upper annular chamber 10 is afforded, into which the outlet 8 opens. In particular, the upper annular chamber 10 transfers the homogenised fluid at low pressure to the outlet 8 of the valve 1 .

The valve 1 comprises an annular passage head 1 1 and an annular impact head 12, which have axial symmetry and are interposed between the lower annular chamber 9 and the upper annular chamber 10.

The passage head 1 1 is integral with the valve body 2.

The impact head 12 is integrally coupled to the lower piston 5 and to the upper piston 6 so as to form an assembled member. For example, the coupling is performed by means of a screw 13, which is part of the assembled organ.

The valve 1 is provided with means for moving the assembled organ in the axial direction towards the passage head 1 1 so that the impact head 12 defines with the passage head 1 1 a gap for the passage of fluid (in this case milk) from the lower annular chamber 9 to the upper annular chamber 10.

In particular, the movement of the assembled member towards the passage head 1 1 contrasts the pressure exerted by the fluid contained in the lower annular chamber 9 on the impact head 12.

Originally, the method also comprises a step of adding to the milk an enzyme preparation based on transglutaminase at a concentration of 0.5-3 units per gram of protein contained in the milk. The transglutaminase is supported on vegetable fibres.

The vegetable fibres supporting the enzyme have high water retention capacity coupled with the presence of glycoproteins. In fact, they contain a special quantity of specific amino acids (in particular lysine) which represent the optimal substrate for the transfer reaction performed by the transglutaminase.

The vegetable fibres therefore act as an active support for the enzyme becoming interposed and covalently bonding between the various caseins and whey proteins thanks to the action of transglutaminase, causing an increase in the water retention of the milk proteins as well as an improvement in the overall structure of the curd.

In the preferred embodiment, the vegetable fibres that support the transglutaminase enzyme are obtained from potato {Solanum tuberosum) and psyllium seeds {Plantago ovata). This choice allows the best performance levels to be obtained in terms of viscosity of the finished product.

Preferably, the vegetable fibres are present in a weight percentage comprised between 5% and 10% of the enzyme preparation.

Preferably, the enzyme preparation comprises demineralized buttermilk as a bulking agent.

In the preferred embodiment, the enzyme preparation is a commercial product known as Reactyn YO+ by the company Campus S.r.l. having its registered office in Via Sala Baganza 3, Quartiere Industriale "I Filagni", 43033 Collecchio (Parma), Italy.

In a first implementation of the method, the addition of this enzyme preparation to the milk takes place prior to the pasteurisation step. In this case, the concentration of transglutaminase is 2-3 units per gram of proteins contained in the milk.

In a second implementation of the method, the addition of this enzyme preparation to the milk takes place after the pasteurisation step. In this case, the concentration of transglutaminase is 0.5-2 units per gram of protein contained in the milk.

The method for making yogurt just described and the use of an enzyme preparation based on transglutaminase supported by vegetable fibres for making yogurt homogenised with a valve having the characteristics described above allows:

- the energy consumption and wear on the components of the homogenising valve to be reduced, thanks to a significant reduction in homogenisation pressure;

- the yogurt production times to be reduced;

the rheology characteristics of the yogurt (such as viscosity and texture) to be preserved without increasing the cost of the recipe.

Such properties have been demonstrated fully by the following three tests performed in a laboratory.

In a first test, the viscosity of the following products was compared:

A- fresh pasteurised semi-skimmed milk

B- fresh pasteurised semi-skimmed milk with the addition of the enzyme preparation based on vegetable fibres and transglutaminase at a concentration of 0.5-2 units per gram of proteins contained in the milk (after the milk pasteurisation step).

Specifically, the enzyme preparation is Reactyn YO+ by Campus S.r.l.

The aim of this first test is to check if the addition of the enzyme preparation based on transglutaminase supported by vegetable fibres allows the homogenisation pressure to be lowered with the same rheology characteristics.

The pasteurisation step, performed in a known way, is followed by the homogenisation step in the homogenising valve 1 described above.

During the subsequent fermentation step, the products were kept at the temperature of 42°C for about 7-8 hours, therefore the pH was lowered to 4.4-4.5. Subsequently, the products were brought to a temperature of about 4°C for storage.

Any curds were broken and smoothed with a 850 micron filter.

The comparison took place after the products had been homogenised in two steps:

- first homogenisation step at different pressures: 80, 150 and 300 bar;

- second homogenisation step at the pressure of 50 bar.

The viscosity, expressed in Cps in the table below, was measured every second for a minute using a Brookfield viscometer with RV03 probe, maintaining a constant temperature of about 4°C. The viscosity values expressed in the table represent the mean of the measured values.

As can be noted from the experimental data obtained, to increase the viscosity of product A (without the enzyme preparation based on transglutaminase supported by vegetable fibres) it is necessary to subject the product to higher homogenising pressures, up to 300 bar.

Instead, for product B, which contains the enzyme preparation based on transglutaminase supported by vegetable fibres, already at 80 bar a higher viscosity is obtained than that obtained with product A at 300 bar.

In a second test, the viscosity of the following products was compared: C- fresh pasteurised semi-skimmed milk with added proteins

D- fresh pasteurised semi-skimmed milk with added proteins and the enzyme preparation based on vegetable fibres and transglutaminase at a concentration of 2-3 units per gram of proteins contained in the milk

(before the milk pasteurisation step)

Specifically, the enzyme preparation is Reactyn YO+ by Campus S.r.l. The addition of proteins to products C and D took place as per the tables below.

The percentage of proteins in product D is equal to 3.51 .

The aim of this second test is to check if the addition of the enzyme preparation based on transglutaminase supported by vegetable fibres allows the homogenisation pressure to be lowered and the protein content to be reduced with the same rheology characteristics.

The pasteurisation step, performed in a known way, is followed by the homogenisation step in the homogenising valve 1 described above.

During the subsequent fermentation step, the products were kept at the temperature of 42°C for about 7-8 hours, therefore the pH was lowered to 4.4-4.5. Subsequently, the products were brought to a temperature of about 4°C.

Any curds were broken and smoothed with a 850 micron filter.

The comparison took place after the products had been homogenised in two steps:

- first homogenisation step at different pressures: 80, 150 and 300 bar;

- second homogenisation step at the pressure of 50 bar.

The viscosity, expressed in Cps in the table below, was measured every second for a minute using a Brookfield viscometer with RV03 probe, maintaining a constant temperature of about 4°C. The viscosity values expressed in the table represent the mean of the measured values.

Compared to the first test, the viscosity differences are less marked. This is due to the fact that product C has about a 0.75% higher protein content than product D, whereas in the first test products A and B have the same protein content. Furthermore, the enzyme preparation based on transglutaminase supported by vegetable fibres was added prior to the pasteurisation step. In any case, it can be noted that - with the same pressure and homogenisation - product D still has a higher viscosity than product C. In particular, the increased viscosity effect for product D is more marked at the minimum pressure of 80 bar. This effect is however less evident at higher pressures since at such pressures the protein complexes formed by the added enzyme preparation are broken up, hence reducing the viscosity.

In a third test, the viscosity of the following products was compared:

E- fresh pasteurised semi-skimmed milk with added proteins

F- fresh pasteurised semi-skimmed milk with added proteins and the enzyme preparation based on vegetable fibres and transglutaminase (supported by vegetable fibres) at a concentration of 1 -2 units per gram of proteins contained in the milk (after the milk pasteurisation step, precisely during the inoculation of the bacterial mixture).

Specifically, the enzyme preparation is Reactyn YO+ made by Campus S.r.l.

The addition of proteins to products E and F took place as per the tables below.

The percentage of proteins in product E is equal to 4.41 . Ingredients of product F Percentage

Semi-skimmed milk (protein content 3.1 - 78.98

3.4%)

Semi-skimmed powdered milk 5.19

Cream 45% 8.33

Sugar 7.50

Enzyme preparation based on 0.06

transglutaminase supported on vegetable

fibres

The percentage of proteins in product D is equal to 4.41 .

Compared to the second test, here the two products E and F have the same protein percentage, therefore the only variable effectively comes from the addition of the enzyme preparation based on transglutaminase supported on vegetable fibres after pasteurisation.

The aim of this third test is to check if the addition of the enzyme preparation based on vegetable fibres and transglutaminase allows the homogenisation pressure to be lowered with the same rheology and protein characteristics.

The pasteurisation step, performed in a known way, is followed by the homogenisation step in the homogenising valve 1 described above.

During the subsequent fermentation step, the products were kept at the temperature of 42°C for about 7-8 hours, therefore the pH was lowered to 4.4-4.5. Subsequently, the products were brought to a temperature of about 4°C.

Any curds were broken and smoothed with a 850 micron filter.

The comparison took place after the products had been homogenised in two steps:

- first homogenisation step at the pressure of 180 bar;

- second homogenisation step at the pressure of 50 bar.

The viscosity, expressed in Cps in the table below, was measured every second for a minute using a Brookfield viscometer with RV03 probe, maintaining a constant temperature of about 4°C. The viscosity values expressed in the table represent the mean of the measured values.

For product E a viscosity of 21347 Cps was measured, whereas for product F a viscosity of 29773 Cps was measured.

From the tests performed, the characteristics of the method for making yogurt, according to the present invention, are clear, as are the advantages.

In particular, the addition to the milk of the enzyme preparation based on transglutaminase supported on vegetable fibres at the indicated concentration and the performance of the homogenisation step in a valve with a double annular chamber allows:

- processing at lower homogenisation pressures (e.g. 80 or 150 bar compared to 300 bar), hence reducing the energy expenditure and the wear on the components of the homogenising valve;

- the yogurt production times to be reduced;

- for the same homogenising pressures, the viscosity of the yogurt to be increased;

for the same homogenising pressures, the protein content to be reduced without affecting the viscosity (which is actually improved), hence also reducing the cost of the recipe.