SYSTEM FOR CONTINUOUSLY TREATING FOOD

Technical Field The present invention relates to system for treating food with a volatile biocide.

Background Art

The preservation of perishable products continues to be the focus of considerable commercial interest. By extending the shelf life of a food product, eg, a processed or cured meat, considerable economic value can be added to that product. Approaches to this end are many and varied, eg, tight control of production and storage conditions, packaging, post and in situ applications of preservatives, and various combinations of these and other techniques are known and in practice to one extent or another. In the context of smallgoods such as hams, bacon, sausages, cured meats, pressed chicken, turkey roll, frankfurts, etc, and baked goods all of these techniques are in use, eg, frozen or refrigerated storage, modified atmosphere packaging, and the addition of preservatives either to the starting material or mix from which the food product is prepared, or the application of a preservative to the finished food product. With respect to the latter, the application of a small amount of preservative to a finished baked good, can extend the shelf life of the baked good from a typical 6-8 days to an extended 14-16 days (all other conditions, eg, packaging, storage conditions, etc, being ■ equal). These preservatives can include a wide variety of biocides (ie, microbiocidal substances, antimicrobial substances, etc) such as acetic acid, lactic acid, carbonic acid, mixtures thereof, and the like.

One problem, however, in the application of a preservative to a food product is to apply the preservative in a manner that does not interfere with the natural organoleptic properties of the product, eg, taste, smell, texture, etc. In the case of applying the preservative to a finished smallgood, too much preservative can impart an unwanted tartness to the product or discolour the product.

Another problem with the application of a preservative to the finished smallgood is consistent application of the preservative in a production line setting. Commercially distributed smallgoods, along with most other commercially manufactured and

distributed perishable goods, are made in large quantities, and consistency from one item to the other is important to the commercial success of the product line. In the case of applying preservative to smallgoods, the amount of preservative applied to the first itemsmallgood in the production cycle should be essentially the same as the amount of preservative applied to the last item in the production cycle (and all items throughout that production cycle, for that matter). This can be difficult to control over extended periods of time due to, among other things, variations in the temperature of the equipment, the preparation and delivery of the preservative to the finished product, and the like. The present applicant has found that this problem is particularly the case with gaseous biocides applied to food products such as smallgoods.

Hitherto, conventional gaseous processes aimed at extending the shelf-life of materials prone to microbial spoilage have relied on modified atmosphere (MAP) procedures. In such procedures, the oxygen gas atmosphere surrounding the material is replaced with a food grade carbon dioxide and/or nitrogen atmosphere, and high barrier co-laminate packaging is used to maintain the exclusion of oxygen from the package. However, MAP processes have disadvantages. That is, whilst it has been found that an extension of the shelf-life can be achieved in respect of materials treated by the procedures, the extension is often limited. Furthermore, considerable costs are involved including the cost associated with the requirement for specialised co-laminate film packaging and the necessity to slow packaging lines to ensure that totality of heat sealing is achieved.

In AU 730402 and US 6224930 (incorporated herein by reference), the present applicant described an alternative method for extending the shelf-life of materials prone to microbial spoilage involving treating a material with a volatile biocidal substance(s) such as a natural food acids (eg. acetic acid) entrained in a defined carrier gas within an evacuated treatment vessel. Subsequently, the present applicant found that it was not necessary to evacuate the treatment vessel in order to achieve a satisfactory extension of shelf-life. This 'no-vacuum' method is described in AU 734421 and US 6265006 (incorporated herein by reference). The process and apparatus described in the above mentioned patent specifications for the generation of the biocidal gas comprised the bubbling of the carrier gas through the liquid volatile biocidal substance or a solution thereof. In the case where the biocidal substance is carbonic acid and the carrier gas carbon dioxide, the carbonic acid was formed in situ by bubbling the carrier gas through water.

The present inventors have now developed a system which provides improved continuous treatment of food with volatile biocides.

Disclosure of Invention In a first aspect, the present invention provides a system for gaseous treatment of food applied in a continuous mode comprising: vessel adapted to receive a volatile biocide and food; entry port for introducing food into the vessel; exit port for removing food from the vessel; means for conveying food through the vessel from the entry port to the exit port; treatment zone for treating food in the vessel with a volatile biocide entrained in a gas stream; means for introducing the volatile biocide containing gas stream into the vessel and substantially evenly distributing the volatile biocide at least across the treatment zone; and means for removing volatile biocide from the vessel, such means being adapted to also remove ambient air entering the vessel through the entry port and the exit port.

The system may further include: biocide measurement and control means to ensure correct amount of volatile biocide is provided and maintained in the vessel during treatment of food.

The system may further include: means to recirculate the biocide containing gas stream and air from the removing means to the introducing means after bleeding off enough gaseous mixture to compensate for air drawn in through the entry and exit ports and adding additional biocide to the gas stream to restore the concentration of the biocide in the gas stream to a desired level.

A proportional chemical dosing pump may be used to meter the biocide into the circulating gas stream to establish and replenish the circulating biocide concentration.

The vessel can be made of any suitable material such as stainless steel, food approved plastic or other suitable materiais for food contact. Typically, the vessel is rectangular in cross section which can assist in the even treatment of food. It will be appreciated that the vessel can have any suitable shape or cross section.

The system according to the present invention is adapted for continuous treatment of foods using a treatment gas containing a volatile biocide. Typically, the food is a substantially solid material for human consumption which is susceptible to microbial spoilage and which has an exposed surface having a water activity of greater than or equal to about 0.85. Preferably, the food is selected from smallgoods, baked goods, cheese, fresh fruit, dried fruit and nuts, fresh pasta, fresh poultry and fish and other manufactured or processed foods.

Preferably, the smallgood is ham, bacon, chicken or turkey or other processed meat. More preferably, the smallgood is ham or similar processed meat. Preferably, the baked goods are crumpets, bread loaves, or the like.

Preferably, the cheese is grated or shredded _, .

Preferably, the volatile biocide is selected from the group consisting of natural food acid, volatile chemical biocide, and mixtures thereof.

Preferably, the natural food acid is acetic acid, propionic acid or mixtures thereof. More preferably, the natural food acid is acetic acid.

Preferably, the concentration of acetic acid in air or carrier gas is between 0.0025 and 0.1 gm/litre. Similarly for other suitable food acids a value of 0.002 to 0.08 gm/litre is usually required for optimum results.

In order to overcome or minimise the risk of explosion in the case that the carrier gas is air the amount of volatile biocide should be less than about 80% of the Lower

Explosive Limit in air (LEL). For acetic acid, the LEL is quoted in the published literature at various levels, the lowest referenced by the present inventors is about 4% v/v or about 0.14 gm/litre.

For propionic acid, the LEL is quoted in the published literature at various levels, the lowest referenced by the present inventors is about 2.9 % v/v or about 0.09 gm/litre.

The application of acetic acid as a preservative to a food product typically begins with the conversion of liquid acetic acid to gaseous acetic acid. This conversion is accomplished by any one of a number of different procedures such as flash evaporation, atomisation, etc, and the gaseous acetic acid is then transported, typically by a carrier gas, to a treatment vessel.

Preferably, the volatile chemical biocide is hydrogen peroxide.

The volatile biocide can be in air or in a defined carrier gas such as nitrogen or carbon dioxide. Preferably, the volatile biocide is in air.

The present inventor has shown that in order to obtain consistent treatment of food, it is important to ensure that there is substantially even distribution of the treatment gas in the form of a volatile biocide to the treatment zone in the vessel. To achieve this aim, the vessel requires means for evenly distributing a volatile biocide to the treatment zone. Examples of suitable distribution means include, but not limited to, fans driven by external motors, equalising, distribution or deflection plenums or baffles, gas diffuser, and the like. Preferably, the distribution means is a gas diffuser, preferably a tunable gas diffuser in which the pressure differential across the diffuser can be adjusted to ensure that the flow of gas through the diffuser is uniform across its whole area. Biocide is preferably directed to the gas diffuser via a distribution plenum. Preferably, the gas ( diffuser is positioned substantially equidistant from the entry and exit ports of the vessel. Preferably, the gas diffuser is positioned across the width the vessel and substantially transverse to the direction of movement of the food through the vessel.

Preferably, the means for removing volatile biocide and air entering the vessel from the entry and exit ports are gas extraction ducts positioned proximal to the entry and exit ports.

Preferably, volatile biocide is added from the bottom of the vessel and removed via the from above the vessel. During use, there is typically a slight pressure differential between the air diffuser and the return ducts. The removed volatile biocide and air are typically recycled through the system and further volatile biocide is added to the gas to maintain the required volumes of gas in the treatment zone. Control of addition of the biocide to the recirculating gas stream can be done automatically using data acquired by online analysis of the biocide concentration in the circulating air (or carrier gas) and passing this data to a Process Logic Controller, or similar device, programmed to regulate the rate of dosage by the proportioning chemical dosing pump. Several methods are available for this analysis including solid state sensors and Near Infra Red (NIR) spectrophotometry. The present author has found that NIR is the preferred method and that both vaporous organic acids and vaporous hydrogen peroxide can be detected for this purpose by the application of ^' NIR spectrophotometry. A suitable analyser is a Servomex Xendos 2500 or similar analyser.

For example, sensors or sampling points can be positioned to measure concentration of volatile biocide at various positions in the system to assist in the control of treatment.

In a second aspect, the present invention provides method for gaseous treatment of food in a continuous mode comprising: providing an system according to the first aspect of the present invention; passing food through the treatment zone of the vessel; and distributing a volatile biocide entrained in a gas stream to the treatment zone in the .vessel so as to evenly expose the food to the biocide for a desired period.

Preferably, the process according to the present invention results in an increase of the shelf life of a food product by about 100 to 400%, more preferably about 300%. With processed hams, for example, the shelf life can be extended to greater than 6 months compared with normally expected 2 month shelf life.

The present inventor has found that the sufficient contacting period is up to about 10 minutes. Preferably, the contacting period is about 5 minutes or less. More preferably, the contacting period is less than about 1 minute. It will be appreciated that the contacting period can depend on the solid material being treated, the type and size of the vessel, and the viable microbial content or bioburden of the material. From the findings of the present inventors, a suitable contacting period can be ascertained for a given food product.

The food may be further processed after treatment for example by slicing, dicing, shredding and packaging. Throughout this specification, unless the context requires otherwise, the word

"comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. Any discussion of documents, acts, materials, devices, articles or the like which ^■ has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed in Australia prior to development of the present invention.

In order that the present invention may be more clearly understood, preferred embodiments will be described with reference to the following drawings and examples.

Brief Description of the Drawings

Figure 1 shows a schematic of one preferred system according to the present invention.

Figure 2 is schematic of a preferred gas distribution means in the form of an air diffuser which is typically positioned to allow entry of the volatile biocide from the bottom of the vessel.

Mode(s) for Carrying Out the Invention Continuous Mode Figure 1 is a schematic representation of a system to facilitate the delivery of the process of this invention to large piece food product, such as, but not limited to, hams, etc in a continuous manner.

Vessel (1) is provided in which to effect the process by containing the treatment gas and is preferably insulated. A recirculating open mesh motorised conveyor (2), or other such means for moving food items (3) for treatment through the vessel (1 ) is employed.

Access and egress to and from the vessel (1) is facilitated by openings (4) at each end of the vessel (1). In-flowing ambient room air (5) is drawn in through the openings (4) to prevent substantial escape of the gaseous biocide. The in-flowing air (5) and the treatment gas containing the biocide is conveyed via a return duct (6) to a fan (8) which induces flow throughout the gas circuit. Balancing baffles (7) modulate the flow from each end (4) of the vessel (1 ) so that flow from each end (4) is evenly distributed. These baffles (7) can be manually set or continuously adjusted by automation provided by the control system. A release baffle (9) can also be adjusted to vent in-flowing air to waste (10) through a biocide eliminating scrubber (not shown). Such adjustment can be controlled automatically by computer software driven control.

Suitable biocide eliminating scrubber can comprise any device which can efficiently remove the biocide, for example a tower packed with media designed to enhance contact between upward flowing waste air carrying unabsorbed biocide and a falling film of water mist. The biocide is absorbed into the water containing an alkali which is neutralised before discharge to liquid trade waste.

Additional ducting (11) to contain and convey the recirculated component of the air, containing a reduced concentration of volatile biocide, is passed to a heater (12) which boosts the recirculated air temperature back to that prescribed for the treatment and on to a proportioning biocide dosing pump and misting nozzle (13) which draws biocide from an adjacent reservoir (14) and injects the biocide into the flowing heated air to facilitate vaporisation, returning the biocide concentration in the returned air to that prescribed for the treatment being undertaken.

A side loop (15) diverts a small portion of this flow to an online biocide analyser (16), the output from which in turn is used as feedback to the control system which adjusts the rate of the proportional pump (13).

The airfiow with the biocide is directed to a distribution plenum (16) via a continuation of the ducting (11) and is evenly distributed by a tuneable air diffuser (17). An example of a suitable tunable air diffuser is described more fully below.

Uniform distribution of the biocide in the carrier gas is a preferred requirement of the process. Numerous unsuccessful attempts were explored prior to achieving satisfactory uniformity of distribution of the biocide in the treating vessel. One means for achieving even distribution was achieved an arrangement for an air diffuser set out in Figure 2 which sits under the treatment vessel (1 ) in Figure 1.

This sub-assembly comprises a distribution plenum (21) which allows the uniform distribution of the air or carrier gas (22), laden with biocide and is further enhanced by a plug filter (23). The air diffuser is equipped with a means of compressing the filter media - a top perforated mesh (24) is pulled towards the supporting perforated . mesh (25) by tightening nuts (26) on threaded rod (27). By increasing the compression on the filter, slight but subtle increases in back pressure can be imparted to the treatment gas to ensure even distribution of the biocide to the treatment zone in the vessel.

Optionally, the entire air diffuser can be removed to facilitate sanitation of the system via a sealed and hinged port (28).

After passing through the air diffuser, the air (or carrier gas) and contained biocide enters the treatment vessel. To assist in the even distribution of the volatile biocide to the treatment zone, the air diffuser is positioned substantially equidistant from the entry and exit ports of the vessel. It has been found that good results can be achieved when the air diffuser is positioned across the width the vessel and substantially transverse to the movement of the food through the vessel.

To convey food through the vessel (1 ), a conveyer arrangement (2) is used. The conveyor preferably allows transmission of the treatment gas there-through. Mesh or gas-impervious materials are suitable in this regard.

The calculated dose of volatile biocide, for example 75% food grade acetic acid, can be generated by calibrated dosing pump, or other suitable means such as pressure displacement, from a reservoir through a spray jet onto evaporation media in an evaporator. Room air, heated to about 3O ⁰ C to 6O ⁰ C by the heater, entrains the volatile acetic acid and conveyed the gas mixture to the vessel via the air diffuser (17). Suitable treatment times were determined by experimentation with the particular product under test to ensure complete equilibration.

For propionic acid, the treatment gas is typically formed by the same method as described for acetic acid.

For hydrogen peroxide, the treatment gas is typically formed by the same method as described for acetic acid. The system of the present invention is particularly suitable for gaseous treatment of food in a continuous mode.

Such food treating process can result in an increase of the shelf life of a food product by about 100 to 400%, more preferably about 300%. With processed hams, for example, the shelf life can be extended to greater than 6 months compared with normally expected 2 month shelf life.

The present inventor has found that the sufficient contacting period in the system is up to ^' about 10 minutes. The contacting period can be about 5 minutes or less. For some food processing, the contacting period can be less than about 1 minute. It will be appreciated that the contacting period can depend on the solid material being treated, the type and size of the vessel, and the viable microbial content or bioburden of the material. From the findings of the present inventors, a suitable contacting period can be ascertained for a given food product.

The food may be further processed after treatment for example by slicing, dicing, shredding and packaging. The system according to the present invention is adapted for continuous treatment of foods using a treatment gas containing a volatile biocide. Typically, the food is a substantially solid material for human consumption which is susceptible to microbial spoilage and which has an exposed surface having a water activity of greater than or equal to about 0.85. The food can be selected from smallgoods, baked goods,

cheese, fresh fruit, dried fruit and nuts, fresh pasta, fresh poultry and fish and other manufactured or processed foods. Typically, the smallgood is ham, bacon, chicken or turkey or other processed meat. The baked goods can be crumpets, bread loaves, or the like. The cheese can be grated or shredded before treatment. The volatile biocide suitable for the system can be selected from natural food acid, volatile chemical biocide, or mixtures thereof. The natural food acid can be acetic acid, propionic acid or mixtures thereof. Acetic acid has been found to provide good treatment of food for the system.

The concentration of acetic acid in air or carrier gas can typically be between 0.0025 and 0.1 gm/litre. Similarly for other suitable food acids a value of 0.002 to 0.08 gm/litre is usually required for optimum results.

In order to overcome or minimise the risk of explosion in the case that the carrier gas is air the amount of volatile biocide should be less than about 80% of the Lower Explosive Limit in air (LEL). For acetic acid, the LEL is quoted in the published literature at various levels, the lowest referenced by the present inventors is about 4% v/v or about 0.14 gm/litre.

For propionic acid, the LEL is quoted in the published literature at various levels, the lowest referenced by the present inventors is about 2.9 % v/v or about 0.09 gm/litre.

The application of acetic acid as a preservative to a food product typically begins with the conversion of liquid acetic acid to gaseous acetic acid. This conversion is accomplished by any one of a number of different procedures such as flash evaporation, atomisation, etc, and the gaseous acetic acid is then transported, typically by a carrier gas, to a treatment vessel.

The volatile biocide can be in air or in a defined carrier gas such as nitrogen or carbon dioxide.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.