WO2015074709A1

WO2015074709A1 - A method and a device for heat treatment of a liquid food product

Info

Publication number: WO2015074709A1
Application number: PCT/EP2013/074473
Authority: WO
Inventors: Kristina PETERSSON; Birgitta Svensson; Anders Löfgren; Christer Lanzingh; Sandra NILSSON
Original assignee: Tetra Laval Holdings and Finance SA
Current assignee: Tetra Laval Holdings and Finance SA
Priority date: 2013-11-22
Filing date: 2013-11-22
Publication date: 2015-05-28
Anticipated expiration: 2016-05-22

Abstract

A method for heat treatment of a liquid food product, comprises the steps of, in a counterflow heat exchanger, directing the liquid food product into the heat exchanger at a first product temperature (t_i1), leading the food product through the heat exchanger and allowing it to exit at a second product temperature (t_o1), directing the heating medium into the heat exchanger at a first heating medium temperature (t_i2), leading the heating medium through the heat exchanger and allowing it to exit the heat exchanger at a second heating medium temperature (t_o2), wherein the temperature difference (dT) between the liquid food product and the heating medium exceeds 5 °C.

Description

A METHOD AND A DEVICE FOR HEAT TREATMENT

OF A LIQUID FOOD PRODUCT

TECHNICAL FIELD

The present invention relates to a method and a device for heat treatment of a liquid food product.

BACKGROUND

In modern liquid processing systems heat treatment is often desirable for making the final product stable during subsequent processing and storage. Such heat treatment, i.e. pasteurization, is normally performed by heating the liquid product to an elevated temperature, which temperature is sufficient to at least prevent microbial growth in the liquid product, as well as keeping the liquid product at that particular temperature for a specific period of time before the liquid product is cooled.

In liquid food processing it is a well known fact that excessive heat load on the food product should be avoided, since heat treatment of the food product may affect the food product negatively, e.g. by causing losses in vitamin and mineral content. At the same time it is critical to ensure sufficient heat load for not jeopardizing food safety. Therefore it is of major importance to control the heating as well as the subsequent cooling of the food product during such heat treatment.

Furthermore, heat treatment of a liquid food product is an energy consuming operation, so energy consuming that a measure of improving (increasing) the efficiency may have a considerable impact on the overall energy consumption during processing of liquid food products.

The present disclosure relates to such improvements.

SUMMARY

It is, therefore, an object of the present disclosure to provide a method and a device for heat treatment of a liquid food product which results in an improved energy efficiency and an associated reduced energy consumption. As a further beneficial effect one or more embodiments also may result in an increased versatility of the device or method, which is elucidated in the detailed description of embodiments.

To this end a method for heat treatment of a liquid food product, comprises, in a heat exchanger, directing the liquid food product into the heat exchanger at a first product temperature, leading the food product through the heat exchanger and allowing it to exit at a second product temperature, directing the heating medium into the heat exchanger at a first heating medium temperature, leading the heating medium through the heat exchanger and allowing it to exit the heat exchanger at a second heating medium temperature,

wherein the temperature difference dT between the liquid food product and the heating medium exceeds 5 'Ό.

In one or more aspects the temperature difference exceeds or equals a temperature selected from the group comprising: 6, 7, 48, 49, 50 'Ό or any interval formed within that group, where denotes all integers between 7 and 48

According to still other aspects a process temperature equals a temperature selected from the group 75, 76, 98, 99 °C or any interval formed within that group, where "..." denotes all integers between 76 and 98. The process temperature may in several embodiments equal the outlet temperature of the product leaving the heat exchanger, yet it may also differ, for example if the temperature is boosted further before the product enters a holding cell. For most embodiments the process temperature may be said to equal the temperature of the product when being in a holding cell.

In one or more aspects the temperature difference is about constant.

The liquid food product may be selected from the group comprising, juice, nectar or still drinks.

In one or more aspects the method may comprise switching from a first liquid food product to a second liquid food product and the step of adjusting the temperature difference based on properties of the second food product for obtaining an optimal heating.

An extended method may also comprise guiding the product to a holding cell, and maintaining the product in the holding cell for a predetermined period of time, and in still other embodiments the product may be redirected through the heat exchanger, now as the heating medium.

The product is maintained in the holding cell

at a at a temperature of about 80 °C for < 15 s, and/or

such as to obtain a pasteurization unit (PU) of at least 0.05 min as determined according to Formula (I):

T-80

PU = t X l(r * ^} (I), wherein t is the holding time in minutes,

T is the effective holding time, °C,

z is the temperature, in °C, and

obtaining a pasteurized liquid food product. According to a related aspect T_HC is about 15 s and t_Hc is about 80 °C.

According to a related aspect T_HC is 15 s and t_Hc is 80 'Ό.Ιη any of the above embodiments the method may be performed when heating a liquid food product as a part of a second pasteurization of the liquid food product.

By using a counterflow heat exchanger the temperature difference may more readily controlled.

According to another aspect the disclosure relates to a control unit for controlling a heat exchanger so as to perform the method according to any

embodiment thereof, as well as to a heat exchanger configured to perform the method according to any embodiment thereof, suggestively controlled by the recently described control unit.

BRIEF DESCRIPTION OF DRAWINGS

The above, as well as additional objects, features, and advantages of the present disclosure, will be better understood through the following illustrative and non- limiting detailed description of preferred embodiments of the aspects of the present invention, with reference to the appended drawings, wherein:

Fig. 1 is a schematic view of a prior art pasteurization system;

Fig. 2 is a flow chart of a method according to an embodiment;

Fig. 3 is a schematic view of a heat exchanger in which embodiments may be applied, as well as illustrative temperature profiles; and

Fig. 4 is a view similar to that of Fig. 3 of yet a further embodiment. DETAILED DESCRIPTION

In an effort to put the present disclosure into its proper context reference is first made to Figs. 1 and 2.

Starting with Fig. 1 a prior art pasteurization system 10 is shown. The system 10 includes a batch tank 1 1 enclosing a certain amount of liquid product to be heated. Upon heating, the liquid product is transported through a heat exchanger 12 wherein the temperature of the liquid product is elevated to a predetermined pasteurization temperature. The liquid product is thereafter kept at the elevated temperature during transportation through a holding cell 13 for ensuring the desired pasteurization. After pasteurization is completed, the liquid product is typically transported through a further heat exchanger 14 for cooling down the liquid product. During heating, a temperature sensor 15 provides a measurement signal representing the current temperature of the liquid product. Additionally, a flow meter 16 provides a measurement signal representing the current flow of the liquid product. The measured temperature is compared with a reference value in a control unit 17 for determining if the actual liquid product temperature is within an allowed pasteurization temperature interval.

Correspondingly, the measured flow is compared with a reference value in a control unit 18 for determining if the actual liquid product flow is within an allowed

pasteurization temperature interval.

Fig. 2 illustrates a flow chart of a method 20 of determining the degree of heat treatment of a liquid product in a liquid product processing system according to an embodiment. The method comprises the step of measuring 21 at least a first real-time value representing the temperature of the liquid product within a first time period. The method further comprises the step of measuring 22 at least a second real-time value representing the flow of the liquid product within the first time period. The method is characterized by the step of calculating 23 at least a first heat treatment index value based on said first and second real-time values, wherein said heat treatment index value is associated with a current degree of heat treatment of the liquid product.

An object of utilizing a heat treatment index value is to replace the individual values of the temp and flow etc, which can be confusing for the operators, as usually numerous flow meters and temperature sensors are provided along the liquid processing system. A further technical effect of the heat treatment index value is that it allows for a lowering of the heat treatment temperature, which normally is set based on a rather large margin of error. The margin of error takes into account position errors of the sensing units, sensor unit deviations, etc. For example, when the liquid product is a beverage it is crucial that the final pasteurized liquid product is fully suitable for drinking, leaving no risk for microbiological growth.

Each calculated heat treatment value may be compared 24 to a heat treatment reference value in order to calculate 25 a value representing a momentary degree of heat treatment of the liquid product for the first time period in view of the heat treatment reference value.

The measurements of the first real-time values and the measurements of the second real-time values as well as the calculations of the first heat treatment index values may be conducted on a continuous basis or at regular predetermined intervals. This results in a set of first real-time values, a set of second real-time values, and a set of first heat treatment index values.

In addition to, or as an alternative to the calculated momentary degree of heat treatment a value representing an accumulated degree of heat treatment of the liquid product may be calculated 26 by performing an integration or summation of at least a first calculated heat treatment index value and a second calculated heat treatment index value over time.

An alternative value representing an accumulated degree of heat treatment of the liquid product may be calculated 26 as a summation of a number values each representing a momentary degree of heat treatment.

The heat exchanger 12 and optionally the holding cell 13 may be said to form a heat treatment device. When applicable the two are arranged in series such that the elevated temperature may be maintained for a predetermined time.

The heat treatment device may preferably be configured for a liquid food product, such as a juice or similar low acid beverage. In case of orange juice the current standard temperature for pasteurization is 95 °C, while the holding cell is configured to maintain the elevated temperature for approximately 15-30 s. However, it has been shown that embodiments of the system will allow a decrease in temperature to 80 °C, without increasing the heat treatment time significantly. Though not being the key for the present invention these effects to will lead to a significant reduction in energy consumption.

Fig. 3 illustrates a heat exchanger 12 which may be used to realize the present invention according to one or more embodiments thereof. Fig. 3 is very schematic and it will also be used to describe a general operation of a heat exchanger as well as some parameters in such operation. Apart from the constructional illustration in the lower portion of Fig. 3, the upper portion of Fig. 3 illustrates the temperature profiles for the product as well as for the heating medium as it passes through the heat exchanger, also in a schematic manner.

In Fig. 3 the product to be heated enters from the right and flows to the left through the central pipe 27, whereas the heating medium enters from the left and flows to the right in the surrounding pipe 28. The illustrated heat exchanger 10 thus utilizes a countercurrent flow, which is particularly beneficial for the purposes described herein. A shorts summary of the denotation used in Fig. 3 reads:

t_M - product temperature when entering heat-exchanger step.

t₀i - product temperature when leaving heat-exchanger step.

t_i2 - temperature of heating medium when entering heat-exchanger step. t_o2 - temperature of heating medium when leaving heat exchanger step

At_m - temperature difference between heating medium and product as a function of position.

The product entering from the right will have a lower temperature t_M

(compared to t₀i ) and as it passes through the inner pipe it will gradually absorb heat from the heating medium conducted through the walls of the inner pipe and have a gradually increasing temperature. As a consequence the heating medium will be cooled as it travels from the left to the right. By balancing the flows it is possible to maintain an almost constant temperature difference At_m (dT in the following for increased readability) between the product and the heating medium for each position in the heat exchanger. A reason for obtaining an as constant dT as possible may be that it may be desired to have a maximum dT while not exceeding a maximum value. A constant dT will then make it possible to obtain an optimal effect. Depending on the flows dT will be higher in the region of the product inlet or in the region of product outlet. For a co-flow heat exchanger, which may be exemplified by switching the flow direction of one of the flows in Fig. 3, it is apparent that the maximum dT is found at the product inlet of the heat exchanger, where the temperature of the product is as low as possible and the temperature of the heating medium is as high as possible.

In one or several embodiments the heating medium may consist of a product to be cooled, thus forming a regenerative heat exchanger with even more beneficial energy efficiency, this may be referred to as product/product heating (or cooling, since the product being the heating medium will be cooled correspondingly, see in particular the upper portion of Fig. 3). In alternative related embodiments the temperature of the heating medium may be adjusted up or down before entering the heat exchanger.

Given that Fig. 3 is schematic it should be emphasized that inventive features may be applied to heat exchangers of various designs. In an actual design the heating may be conducted in several steps, and the product/product heating (or cooling) may e.g. be used in a first heating step or an intermediate heating step, wherein the last heating is performed using another heating media, such as hot water or steam to boost the temperature up to a desired temperature. The preferred relationship for dT may be applicable for any heat exchanger in this steps. A counterflow heat exchanger may preferred for maintaining a constant temperature difference dT, however within that specification there are numerous types of heat exchangers to chose from, such as plate heat exchangers, tube heat exchangers or scraped surface heat exchangers. A typical tube heat exchanger would, in contrast to the one of Fig. 3, typically comprise several parallel pipes for leading the product, even though Fig. 3 only illustrate a single pipe in each direction. A typical tube heat exchanger installation is shown in

WO0031489 to the present applicant. Further, a co-flow heat exchanger could also be utilized.

In the embodiment illustrated in Fig. 4 further features have been added. In this embodiment the product, once having reached the desired temperature, is guided to a holding cell. In the holding cell the product is maintained at a specific temperature or within a specific temperature interval for a specific period of time. The holding cell may be a container or vessel, yet for a well defined process it may be preferred for the holding cell comprises a specified length of pipe. It should be noted that there may be additional heat exchangers or heaters arranged to boost the temperature of the product before it enters the holding cell. In the holding cell a predetermined

temperature t_Hc is maintained for a predetermined period of time T_Hc- According to one aspect t_Hc is defined by75 °C < t_Hc < 95 °C and wherein the predetermined period of time T_HC is about 20 s or less. According to one specific embodiment t_Hc is about 80 °C and T_HC is <15 s, such as 15 s.

The concept, function and properties of a holding cell as such is well known in the art. After passing the holding cell the product is lead back to the heat exchanger such that the product having passed the holding cell is cooled as it passes its heat to the product travelling towards the holding cell.

Most heat exchanger systems used in liquid food processing are designed and dimensioned for processing of dairy products, and the same systems are utilized for juice, nectars, still drinks etc. For this reason the systems of today operates at a temperature difference of about 3-5 °C. In the present invention a method for heating a liquid product has been optimized for juice, nectars and still drinks having a pH of about 4.2 or less, for example 3.8 or less. Moreover the process is according to one or several embodiments limited to a second pasteurization, i.e. the pasteurization performed immediately before filling into consumer containers (as opposed to the first pasteurization which is generally performed prior to storage of the product). With this starting point the work leading up to the present invention according to many of its embodiments comprised several unexpected results. PRODUCT

The product selected was orange juice with a pH of 4.2 or less and 1 1 .5 °Brix. The orange juice was made from concentrate.

Orange juice, as well as most other juices, is pasteurised at least twice before it reaches the consumer (except for a small amount of NFC being filled directly into consumer packages). The first pasteurisation occurs immediately after extraction prior to bulk storage, and the second pasteurisation occurs before packaging. The first pasteurisation is necessary to inactivate the enzyme pectin methyl esterase (PME) which may otherwise cause cloud loss in liquid food products such as juice, nectars and still drinks. This is of even more concern when the liquid food product is a concentrate. Microorganisms of commercial interest, e.g. yeast, pathogens, mould etc are also killed by this process. The second pasteurisation destroys any

microorganisms that may have (re-)contaminated the liquid food product after the first pasteurisation step and survived bulk storage, as well as those which may have (re-)contaminated the liquid food product during its reconstitution from concentrate. As one example the concentrate is diluted with potable water.

Generally the first pasteurization step is performed close to the harvesting site, or even at the harvesting cite, i.e. juice extract is collected can be divided into juice from concentrate (FC) , juice not from concentrate (NFC), and freshly squeezed orange juice. Freshly squeezed orange juice is not pasteurized and thus has a rather short period in which it should be consumed. FC and NFC are generally subjected to a first pasteurization to inactivate/kill pectin methyl esterase, as well as other organisms. The juices are after the pasteurization optionally concentrated in order to obtain FC. FC is for example stored aseptically or frozen, for example at temperatures from -6 to - 25 °C. The demands depend on the type and quality of the juice and are within the capacity of the skilled person to control. NFC is after the pasteurization stored frozen, for example in drums at -18 °C or lower; or chilled (in large containers at around -1 to 1 ^<C).

Generally any pasteurization temperature and time conventionally used for the particular liquid food product, i.e. necessary to achieve the desired level of

pasteurization, depend on the quality of the fruit and fruit extract. For example orange juices are pasteurized between 95-98 °C for 10-30 s. Generally the pasteurization should not be less than 72 °C for 15 s as otherwise pathogenic bacteria such as Salmonella, Listeria or E.coli may be present.As used herein "D-value" refers to decimal reduction time and is the time required at a specified temperature to kill 90% of the organisms being studied. When referring to D-values it is proper to give the temperature as a subscript of the "D".

As used herein "z-value" is a term used in thermal death time calculations.

The z-value of an organism is the temperature, in degrees Celsius, that is required for the thermal destruction curve to move one log cycle. It may be simplified as the temperature required for one log reduction in the D-value. While the D-value gives the time needed at a certain temperature to kill an organism, the z-value relates the resistance of an organism to differing temperatures.

As used herein a "heat exchanger" is a system built for energy transfer from one medium to another.

As used herein the term "juice" is naturally contained in fruit or vegetables. It is prepared by mechanically squeezing or macerating fresh fruits or vegetables. Juice is 100 % fruit juice. Examples of juices are orange and apple juice, another example is juices containing juice from multiple fruits, for example orange/pineapple. As used herein the term "nectar" refers to fruit or vegetables but with a 25-99 % juice content and usually with added sugar. Examples of nectar are orange nectar, and nectar containing multiple fruits such as apple, pineapple, orange, and

passionfruit.

As used herein "still drinks" contain 0-24 % juice content in fruit, vegetable or other flavours. Example of still drinks are energy drinks such as Powerade marketed by the Coca Cola Company, ice tea, fruit drinks such as Festis marketed by Carlsberg.

TESTS

Orange juice is normally processed with a dT of 3-5 °C and a process temperature of 95 °C. In the presents tests the orange juice was processed using standard equipment yet not with standard operating parameters.

A summary of the process parameters are found in the numbered list below. The first temperature is the process temperature of the liquid product, after heating, and dT is the temperature difference of the liquid product :

1 ) 80 ^<C / dT=3 ^<C

2) 80 ^<C / dT=15 °C

3) 95 °C I dT=5 °C (baseline, reference sample, normal processing)

4) 95 ^<C / dT=12 °C

5) 95 ^<C / dT=25 °C

VALIDATION

In the validation three parameters were selected. The baseline used for comparison was orange use treated in a conventional manner.

1 ) Vitamin C content

The vitamin C content was measured after 3.5 months and after 6 months using HPLC (High-Performance Liquid Chromatography).

2) Taste

A trained panel used the ISO norm 4120, 2004 in a "Sensory analysis- Methodology-Triangle test" to determine taste. This means that in a given test there is three samples. One sample is the test sample and the other two are reference samples. The task is to select the odd one out. The panel was trained according to international standards (ISO-8586) and the statistical evaluation was performed using a special data collection system. Evaluations were made immediate after production and the once a month. 3) Visual appearance

The visual appearance of all samples was compared during storage. Photos were acquired using a DigiEye camera, i.e. camera mounted in a photobox making it possible to take pictures under controlled and consistent light conditions in order to compare product appearance during storage.

RESULTS

1 ) Vitamin C content

There was no significant difference in vitamin C content between the tests and the baseline.

2) Taste

No significant taste difference detected during 7 months of storage.

3) Visual appearance

As expected there was a change in color over time, all samples had a darker yellow color after 7 month storage as compared to after 3 months storage, yet there was no difference between test samples and the baseline.

The tests and validations verify that the alterations made in the tests may be made without jeopardizing the quality of the product in question as compared to the baseline. This result was perceived as surprising, particularly since there is a long tradition in the business of using processing lines using parameters from the dairy business also for juice, nectars and still drinks.

Benefits of the method according to one or more embodiments include that the increase temperature difference dT results in a more efficient heat transfer process, which reduces the energy consumption. The surprising result that the product quality in accordance with the used indicators was not affected by the quite large variation in dT as compared to a baseline also results in an increase versatility. Various products within the field of juices, nectars and still drinks may have different properties in terms of viscosity, specific heat etc, all affecting a heat transfer process. Instead of tailormaking systems for each of these products use may be made of a variation of dT. This means that transitions between operating conditions when changing from a first product to a second may be made swiftly and with ease.

In some embodiments the X< dT < Y °C, wherein X independently of Y is selected from the group consisting of 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, 14, 15, 16, 17,18, 19, 20, 21 , 22, 23, 24, 25, 26, 27, 28, 29, 30, 31 , 32, 33, 34, 35, 36, 37, 38, 39, 40, 41 , 42, 43, 44, 45, 46, 47, 48, 49, and Y independently of X is selected from the group consisting of 6, 7, 8, 9, 10, 1 1 , 12, 13, 14, 15, 16, 17,18, 19, 20, 21 , 22, 23, 24, 25, 26, 27, 28, 29, 30, 31 , 32, 33, 34, 35, 36, 37, 38, 39, 40, 41 , 42, 43, 44, 45, 46, 47, 48, 49, 50.

As used herein in connection with specified temperatures "about" is intended to mean +/- 3 'Ό. Generally whenever a specific temperature or interval or

temperatures are given without the wording "about" there is a tolerance allowing the temperature to vary slightly such as +/- 1 °C.

While the solution has been described with reference to specific exemplary embodiments, the description is generally only intended to illustrate the inventive concept and should not be taken as limiting the scope of the solution.

Claims

1 . A method for heat treatment of a liquid food product, comprising, in a heat exchanger,

directing the liquid food product into the heat exchanger at a first product temperature (t_M ),

leading the food product through the heat exchanger and allowing it to exit at a second product temperature (t₀i ),

directing the heating medium into the heat exchanger at a first heating medium temperature (t_i2),

leading the heating medium through the heat exchanger and allowing it to exit the heat exchanger at a second heating medium temperature (t_o2),

wherein the temperature difference (dT) between the liquid food product and the heating medium exceeds 5 'Ό.

2. A method according to claim 1 , wherein the temperature difference (dT) exceeds or equals a temperature selected from the group comprising: 6, 7, 48, 49, 50 'Ό or any interval formed by two individual temperatures within the group.

3. A method according to claim 1 , wherein a process temperature equals a temperature selected from the group 75, 76, 98, 99 °C or any interval formed by two individual temperatures within the group.

4. A method according to claim 1 or 2, wherein the temperature difference is constant.

5. A method according to any preceding claim, wherein the liquid food product is selected from the group comprising, juice, nectar or still drinks.

6. The method of any preceding claim, said method further comprising the step of switching from a first liquid food product to a second liquid food product and the step of adjusting the temperature difference (dT) based on properties of the second food product.

7. The method of any preceding claim, further comprising:

guiding the product to a holding cell, and

maintaining the product in the holding cell for a predetermined period of time.

8. The method of claim 7, further comprising redirecting the product through the heat exchanger, now as the heating medium.

9. The method of claim 7 or 8, wherein the product is maintained in the holding cell

at a at a temperature (T_HC) of about 80 °C and wherein t_Hc ≤ 15 s, and/or such as to obtain a pasteurization unit (PU) of at least 0.05 min as determined according to Formula (I):

T-80

PU = t X l(r * ^} (I), wherein t is the holding time in minutes,

T is the effective holding time, °C,

z is the temperature, in °C, and

obtaining a pasteurized liquid food product.

10. The method of claim 9, wherein T_HC is 15 s and t_Hc is 80 °C.

1 1 . The method according to any preceding claim, said method being performed when heating a liquid food product as a part of a second pasteurization of the liquid food product.

12. The method of any preceding claim, wherein the heat exchanger is a counterflow heat exchanger.

13. A control unit configured to perform the method steps of any of the claims 1 to 1 1 in a heat exchanger, such as a coflow heat exchanger or a counterflow heat exchanger.

14. A heat exchanger comprising a control unit of claim 13 and configured to perform the method of the claim selected from the group comprising: claim 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 and 12, or combinations thereof.