GB2528045A

GB2528045A - Thermal treatment of food products

Info

Publication number: GB2528045A
Application number: GB1412019.0A
Authority: GB
Inventors: Richard Geoffrey Walden; John David Emanuel
Original assignee: Zinetec Ltd
Current assignee: Zinetec Ltd
Priority date: 2014-07-06
Filing date: 2014-07-06
Publication date: 2016-01-13
Also published as: GB201412019D0

Abstract

A thermal treatment process for the in-container sterilisation of liquid-based foods and beverages (including those containing particles) wherein sufficient agitation in a heating phase results in sterilization values (F0s) with a ratio of maximum F0 to minimum F0 in the range of 1.0 to 2.0. The foods and beverages may have viscosities that, in the absence of agitation, would result in heating largely by conduction. These foods may be soups, sauces, ready meals, baby foods, milk or protein based beverages, desserts and pet foods. Preferably the agitation is horizontal reciprocal agitation. A method to establish appropriate sterilization values (F0s) is also disclosed. Heating data is established for a test container equipped with a plurality of thermocouples located in predetermined positions. The test container is filled with the food product of interest. The F0 values are determined in different parts of the test container. Thus the ratio between the values of the maximum and minimum F0 within the container for the given food or beverage can be calculated.

Description

THERMAL TREATMENT OF FOOD PRODUCTS

TECHNICAL FIELD

This invention is concerned with the thermal treatment of food products to achieve sterilisation by heat to provide for the foods to be preserved in sealed containers safely and indefinitely. Such treatment has been known for some two hundred years and retorts that provide for the heat treatment of cans, jars, pouches, or other containers under pressure are widely used in the food industry around the world.

BACKGROUND ART

Retorts currently in use for food processing fall into two main categories, static and agitating. Most agitating retorts are rotary'. Each of these subdivided into batch and continuous. The most common retorts are static' and in batch format is the simplest and least expensive type. They are heated by steam and/or hot water under pressure and cooled by cold water. In static retorts the heat is conducted into conduction products' causing a gradation in temperature from the product in contact with the inside wall of the container to the product at the centre farthest from the source of heat.

At the start of the heating phase the temperature of the product against the wall of the container will quickly approach the retort temperature whereas the temperature of the product located towards the centre of the container will rise only slowly as the heating phase proceeds. In order to safely sterilise the whole of the contained product (with a pH>4.5) a suitable sterilisation value (Fo), defined below, must be achieved in the coldest region, the cold spot' of the container, usually close to the centre. The hotter regions closer to the wall of the container will thus be subject to unnecessarily high Fo's.

During the cooling phase a gradation in temperature occurs and cooling faster in the hotter regions provides some reduction in the ratio between the values of the highest and lowest Fo's. Many food products including soups, sauces and dips, ready meals', ground meats, baby foods and pet foods are conduction products' but liquid to a greater or lesser extent.

Thinner liquid products heat by convection Convection products' so the differences in heating and cooling rates and in Fo's can be less marked but nevertheless significant. These products include consommés and other thin soups, some vegetables in brine, milk based beverages and the like.

Definition -Sterilisation Value (Fo') The degree of sterilisation for a wide range of products for which pH is above 4.5 (low-acid), is expressed as rT-12u Fo=flOL Z di Where: 121.1°C is reference temperature, T°C is the sterilisation temperature, t is the sterilisation time (mm), and z is temperature difference required for a 10-fold change in thermal death time. The usual reference organisms are spores of Clostridium Botulinum giving z =10°C.

It is essential for safety to determine the temperature and time necessary to produce a sterile product. For low acid products (pH>4.S) this means achieving a set minimum Sterilisation Value (Fo), often to a minimum value of 6. Depending on the exact nature of the product, Sterilisation Values in the range Fo = 3 -20 would generally be necessary to ensure food safety.] Rotary retorts are the other major category of retort in common use.

In these, the containers are rotated inside the retort to induce some mixing and thus reduce the temperature differences within the container during both the heating and cooling phases, reducing the ratios between the values of the highest and lowest Fo's. The difference in Fo between the product at the at the colder regions, generally towards the centre, and that in other areas of the container is less marked than with static retorts, though generally it is still undesirably high.

In an ideal thermal process there would be little or no difference between the sterilisation values, Fo's, of all the food or beverage within the containers both at the end of heating and during and after cooling.

All the food would receive the same degree of sterilisation; none would be over-sterilised with the likelihood of overcooking and degradation.

Heretofore thermocouples and equivalent probes have been deployed to determine the coldest spot in a container, the cold spot'. Adequate sterilisation at the cold spot, measured by Fo value, ensured that the entire product in the container had been sterilised. The degree of over-sterilisation of product away from the cold spot was rarely determined as no satisfactory method of avoiding such over-sterilisation was available. For many products, over-sterilisation results in over-cooking, possibly scorching or degrading a significant part of the product. Over-cooking is an important contributing factor to the less than excellent quality of many preserved foods.

By using a procedure in which a number of thermocouples, or equivalent devices, are deployed within single containers, minimum and maximum Fo's can be measured and used to help optimise the degree of agitation for a thermal process.

DISCLOSURE OF THE INVENTION

According to a first aspect of the present invention there is provided a thermal treatment process for the in-container sterilisation for long term storage at ambient temperature of liquid-based foods and beverages (including those containing particles) which without agitation would heat largely by conduction wherein the entire liquid contents of a single container is subject to sufficient agitation such that at the end of the heating phase sterilisation values (Fo's) are controlled to provide that within the container the ratio of maximum Fo to the minimum Fo lies in the According to a first preferred version of the first aspect of the present invention the entire liquid contents of a single container is subject to sufficient agitation in heating and cooling phases such that at the end of the heating and cooling phases total sterilisation values (Fo's) are controlled to provide that within the container the ratio of maximum Fo to the minimum Fo lies in the range of 1.0 -1.5.

According to a second preferred version of the first aspect of the present invention or of the first preferred version thereof the process provides for the controlled horizontal reciprocal agitation of the or each container sufficient to provide for the rapid achievement of even temperature distribution throughout the contents of the or each container.

According to a third preferred version of the first aspect of the present invention or the first preferred version thereof the process provides for some other form of agitation than horizontal reciprocal agitation.

According to a fourth preferred version of the first aspect of the present invention or any preceding preferred version thereof the or each container contains foods or beverages which has a pH >4.5.

According to a second aspect of the present invention there is provided a method to establish appropriate Fo values for the process of any preceding claim characterized by the establishment of heating data by utilizing a test container equipped with temperature sensors such as thermocouples and filled to an appropriate extent with the food product of interest to determine the values of Fo in different parts of the test container and thus the ratio between the values of the maximum and minimum Fo within the test container for the given food or beverage.

According to a third aspect of the present invention there are provided contained products processed according to the first aspect of the present invention r any preceding preferred version thereof including soups, sauces, dips, ready meals', baby foods, milk-based and other protein-based beverages, desserts and pet foods.

According to a first preferred version of the third aspect of the present invention products produced by a process according to the first aspect including catering products and preserved ingredients for subsequent use in preparation of other food products.

According to a fourth aspect of the present invention there is provided a process according to the first aspect or any preferred version thereof wherein the sterilising step is replaced by a pasteurisation step.

According to a first preferred version of the fourth aspect of the present invention contained foods and beverages including soups, sauces, dips, ready meals', baby foods, milk-based and other protein-based beverages, desserts and pet foods.

According to a second preferred version of the fourth aspect of the present invention contained foods and beverages including catering products and preserved ingredients for subsequent use in preparation of other food products.

According to a fifth aspect of the present invention there is provided a method of establishing appropriate Fo values for the processing according to the first aspect of the present invention as hereinbefore described with reference to the accompanying figures.

This invention discloses an improved agitating batch retort process and control procedure to sterilise many fluid foods and beverages in containers for long term storage at ambient temperature. It also discloses preserved foods and beverages made by this improved process and that are essentially evenly sterilised or pasteurised throughout the contents of the containers to a desired degree of sterilisation or pasteurisation.

A process and control procedure is disclosed in which the process uses essentially horizontal reciprocal agitation or possible alternative forms of agitation of sufficient vigour to induce rapid and thorough mixing of the fluid content and the control procedure may include the use of multiple thermocouples or equivalent to determine the agitation conditions required to achieve sufficient temperature homogeneity within the fluid phase of the chosen product to produce essentially even sterilisation throughout that product. Different products with, for example, different viscosities will require different agitation conditions to achieve essentially even temperature distribution and thus even sterilisation.

Brief Description of Drawings

Exemplary embodiments of aspects of the invention will now be described with reference to the accompanying figures of which: Figure 1 shows two food container equipped with thermo couples; and Figure 2 is a table showing the effect of varying agitation on the containers of Figure 1 as revealed by the thermocouples including the relationship between maximum and minimum Fo.

Description of Embodiment

Trials were undertaken using a retort fitted with a horizontal agitating mechanism designed to agitate sample containers within the retort.

This retort, with the agitator switched off, acted as a static retort. With low speed agitation it acted as a relatively novel gentle motion' retort using a gentle back and forth motion. It could also employ more vigorous horizontal reciprocal agitation. In addition tests were carried out in an end-over-end rotary retort.

For each retort system 73mm diameter x 110mm high cans (Can 1, Can 2, Figure 1) were made up, each containing four thermocouples (Can 1 TO 2 -TC4; Can 2 TCS to TC8) and filled with 5% CoIflo 67 starch solution as a food simulant, leaving a 32m1 free space (F, Can 1). All agitating processes require a free space or headspace in the container to allow the product to move. Thermal processes were then run using each of the four retorting processes above at a variety of conditions as specified in the tables below to measure the variability of sterilisation values, Fo's, within each test container.

For the static', gentle motion' and vigorous horizontal' process trials, cans, each with four thermocouples, were mounted in the retort fitted with the horizontal agitating mechanism. In the first series cans with the thermocouples vertical and sensing tips down were used as per drawing Can 1. In the second series the thermocouples were positioned as per drawing Can 2 but rotated so that the thermocouples were horizontal. Thermal processes were then run with each of the above retorting systems using the same retort temperature (1 25°C) until a minimum sterilisation valve of FoG was reached before cooling the containers In the end-over-end rotary retort four thermocouples positioned in a single can as per drawing Can 1 were used and the can mounted in the retort with the thermocouples horizontal. Rotation speeds of 7 and 1 5 rpm were selected, around 7 being typical and 1 5rpm towards the high end of conditions commonly used. The thermal processes were run at 121°C due to the limitations of the equipment and the results then transposed to 125°C by calculation.

It is well established that, for a given product, the rotary process has an optimum speed of rotation for optimum agitation. Too slow, and the product could mix better; too fast and gravity does not have time to overcome the combination of product viscosity and centrifugal force to enhance mixing.

In static processing with conduction products large differences between the highest and lowest Fo's are to be expected and in fact are even larger than shown in these experiments in which thermocouples were positioned a minimum of some 9mm away from the inside wall of the container. During a process to generate Fo6 at the coldest spot, the product adjacent to the inside wall of the can will experience virtually retort temperature for the entire sterilisation period, giving in this case an Fo of around 120, and a ratio of 1 20:6 = 20:1. The drawing shows the position of the thermocouples within a test can.

Note that Can 2 was rotated so that the thermocouples were horizontal. The fastest heating thermocouple is that nearest the can wall (TC6) and the slower farther away. The variation in total Fo's was slightly less than at the end of heating as the fastest heating regions would also be the fastest cooling. It is likely that in many products the taste, colour, texture and vitamin retention will be adversely affected by the static process.

The "gentle motion" system which uses agitation rates in the range S -rpm, in these experiments showed Fo ratios similar to or even higher than those with static processing. It seems probable that the gentle agitation produces a degree of mixing towards the edges of the container (TC's 2,4,6 & 8) but leaves the product nearer the centre relatively undisturbed thereby increasing the ratio; further investigation is beyond the immediate scope of this patent application. However at 60rpm around a 1 5% reduction in total process time was noted compared with static processing. The quality of products sterilised by this process is also likely to be adversely affected by the variability of the sterilisation process throughout the products in the containers, with some of the product over-cooked.

End-over-end rotary processing showed less variation than static though in the worst case, at end of heating and higher temperature,

II

nevertheless a ratio of over 2:1. As with static processing the faster heating regions cooled the fastest and vice versa so after cooling there is less variation in total Fo. Similar results have been seen in previous experiments. Products sterilised by the rotary process are likely to be better than those processed in static or gentle motion processes but still far from ideal.

Using vigorous horizontal agitation and selecting conditions sufficiently vigorous to generate essentially homogeneous temperatures throughout the contents of the containers it was possible to reduce the ratio of maximum to minimum Fo within the containers very significantly in comparison with static, rotary and gentle motion retort processes. At agitation rates of 120 rpm the maximum to minimum ratio was 1.1:1.0 and at higher agitation conditions the ratio was 1.03:1.00, essentially ideal with respect to both Fo at the end of heating and at the end of the process after both S the heating and cooling phases. Unlike rotary retorting, where, as discussed above, the rate of agitation goes through an optimum, horizontal agitation appears to improve and then plateau.

Foods and beverages sterilised in this way will be very evenly sterilised without the need to over-sterilise and thus over-cook any part and will therefor retain their taste, colour, texture, vitamins and other organoleptic qualities to a level largely unprecedented in batch thermal processing of conduction products.

With vigorous horizontal agitation it is also reasonable to assume that as the thermocouples in 7 different positions (1 and 5 being equivalent) in the container all give results very close to each other the maximum Fo spread will be only minimally greater than seen in these experiments. The other processes, by contrast, showed large differences in maximum and minimum sterilisation values; other positions showing even greater differences are therefore almost certain to exist. As discussed above this is certainly the case with static processing.

In separate experiments a largely transparent product simulant with indicator particles was packed in a glass container and mounted in the retort fitted with the horizontal agitating mechanism and a video camera was mounted on the mechanism so that the form of the agitation of the product simulant could be observed. Under static' conditions, no mixing could be seen. Under gentle motion' conditions, the product simulant moved back and forth in the container in a gentle wave-like manner with movement at the surface but with little observable mixing.

Under vigorous agitation' conditions, as the agitation rate increased, the product first stirred and then mixed in an increasing chaotic and much more thorough manner, no longer wave like but with the liquid shattering into rapidly changing drops and blobs'.

Similar experiments have been carried out, not by the claimant, for the rotary process and they show the optimum speed effect mentioned above. The experiments also showed that even at optimal conditions the degree of mixing falls far short of that seen under the vigorous horizontal agitating conditions.

INDUSTRIAL APPLICABILITY

Food processing in containers is a worldwide practice. The present invention provides means for the effective and efficient processing of foods offering benefit over existing processing methods. From the experiments described above it is evident that it is possible to in-container sterilise food in a manner that produces little variation in sterilisation value throughout the entire contents of each container.

In these experiments it was achieved using horizontal agitation of sufficient vigour but other agitation modes may possibly also be used.

Claims

CLAIMS1 A thermal treatment process for the in-container sterilisation for long term storage at ambient temperature of liquid-based foods and beverages (including those containing particles) which without agitation would heat largely by conduction wherein the entire liquid contents of a single container is subject to sufficient 25 agitation and sterilisation in a heating phase such that at the end of the heating phase sterilisation values (Fo's) are controlled to provide that the ratio of maximum Fo to the minimum Fo lies in the range of 1.0 to 2.0.
2 A process as claimed in Claim 1 wherein the entire liquid contents of a single container is subject to sufficient agitation and sterilisation in heating and cooling phases such that at the end of the heating and cooling phases total sterilization values (Fo's) are controlled to provide that the ratio of maximum Fo to the minimum Fo lies in the range of 1.0 -1.5.
3 A process as claimed in Claim 1 or Claim 2 wherein the process provides for sufficient controlled horizontal reciprocal agitation of the or each container to provide for the rapid achievement of even temperature distribution throughout the contents of the or each container.
4 A process as claimed in Claim 1 or Claim 2 providing some alternative form of agitation than horizontal reciprocal agitation.

A process as claimed in any preceding claim in which the, or each, container contains foods or beverages which have a pH > 4.
5.
6 A method to establish appropriate Fo values for the process of any preceding claim characterised by the establishment of heating data in which a test container is equipped with a plurality of thermocouples located in predetermined positions within the test container and filled to the appropriate extent with the food product of interest to determine the values of Fo in different parts of the test container and thus the ratio between the values of the maximum and minimum Fo within the test container for the given food or beverage.
7 Contained products produced by a process as claimed in any of preceding claims 1 to 5 including soups, sauces, dips, ready meals', baby foods, milk-based and other protein-based beverages, desserts and pet foods.
S Products produced by a process as claimed in any of preceding claims 1 -S including catering products and preserved ingredients for subsequent use in preparation of other food products.
9 A process as claimed in any of preceding claims 1 -8 in which the sterilizing step is replaced by a pasteurisation step.
Foods and beverages as claimed in claim 9 including soups, sauces, dips, ready meals', baby foods, milk-based and other protein-based beverages, desserts and pet foods.
11 Foods and beverages as claimed in claim 9 including catering products and preserved ingredients for subsequent use in preparation of other food products.
12 A method of establishing appropriate Fo values for the process of any preceding claim as hereinbefore described with reference to the accompanying figures.