GB2409958A

GB2409958A - Method for opening stomata and disinfecting vegetable material

Info

Publication number: GB2409958A
Application number: GB0507168A
Authority: GB
Inventors: Malcolm Read; Charlotte Mcluskie; Michael Hind; Sean Boland
Original assignee: TELFER FOODS Ltd
Current assignee: TELFER FOODS Ltd
Priority date: 2001-08-09
Filing date: 2001-08-09
Publication date: 2005-07-13
Anticipated expiration: 2021-08-09
Also published as: GB0119455D0; GB2378631B; GB2378631A; GB0507168D0; GB2409958B

Abstract

A method for disinfecting a plant leaf, plant stem, or part thereof, said method comprises the steps of providing a plant leaf, plant stem, or part thereof; in a first zone causing stomata to open on the plant leaf, plant stem or part thereof using a stomata opening agent; and in a second zone treating the plant leaf, plant stem or part thereof from step (ii) with a disinfectant whilst the stomata opened in step (ii) remain open. The agent used to open the stomata may be ozone or potassium chloride. The sterilisation may be done by exposure to a variety of chemicals, including ozone, but is preferable done by exposing a suspension of vegetable material to ultra-violet radiation.

Description

METHOD FOR DISINFECTING VEGETABLE MATERIAL

Background to the invention

Herbs, salad vegetables and other vegetable material need to be disinfected before they are used in the manufacture of food products, especially if they are to be used in chilled food products, or before they are packaged for sale to the consumer as ready-to-eat products. This is because they are known to be carriers of bacteria, yeasts and moulds, and other micro-organisms. These can include pathogenic bacteria and viruses which can cause food poisoning in the consumers of the foods. The micro-organisms may also cause spoilage of the herbs and salad vegetables or of the foods in which they may have been used.

Techniques for treating (decontaminating or disinfecting) herbs, salad vegetables and other vegetable material for use as foods or in prepared foods are well known, but none appear to be really suitable for providing properly disinfected herbs and salad vegetables, especially those destined for use in the manufacture of chilled foods.

This can be for any of the following reasons: (a) because they result in vegetable material that are no longer considered fresh; (b) because the techniques are not legal; (c) because the techniques are not liked by consumers) (d) because the techniques do not result in vegetable material that has a sufficient degree of disinfection; or (e) because the techniques may cause organoleptic defects in the vegetable material.

Treatments such as drying, and pasteurizing or sterilizing by the application of heat or steam or microwaves will produce vegetable material that would not be considered to be fresh and therefore would be unsuitable for use in chilled foods. Treatment with ethylene oxide as a sterilising agent is no longer legal in many countries, including those of the European Union. Treatment with ionising irradiation, while it is now legal in many countries and is capable of producing sterile vegetable material that would still be considered fresh in appearance and taste, is regarded with great suspicion by many consumers.

Other known treatments such as washing in baths of disinfecting solutions (e.g. solutions of acetic acid, vinegar, or chlorine) with or without the incorporation of aeration such as in a jacuzzi-type bath, do not produce a great enough microbiocidal action if the vegetable material is to be used in chilled products. At certain high concentrations, they may also introduce organoleptic defects, such as a residual vinegar or chlorine taste.

UV-C radiation has been suggested to provide effective surface disinfection of food products. UV-C is a disinfective mechanism because UV-C radiation is absorbed by the nucleic acids of a cell, to change the cell structure and destroy the genetic information and kill the cells.

"Innovations in Food Technology", May/June 2001, "UV Disinfection in the Food Industry" describes a UV disinfection system for packaging whereby two UV spot lamps are retro-fitted to existing packaging machines. Also, a product on the market by UV Systems Plc is disclosed to disinfect the surface of various food products. The process involves mounting UV lamps across a conveyer belt and passing the food product along the conveyer belt under the l lamps. Both of these methods have the disadvantage that only the upper surface of the food product that is exposed to the UV radiation will be disinfected. This is because the UV lamp(s) is mounted on one side only of the food product. Where the food product exists as more than one layer on the conveyer belt, the lower layer of food product will not be exposed at all to the UV-C radiation and thus will not be disinfected.

In view of the above, the present inventors have identified that there exists the need to develop a new method for disinfecting vegetable material that is safe and effective.

Accordingly, it is an aim of the present invention to provide a new, safe, and effective method for disinfecting fresh or individually quick frozen vegetable material.

Furthermore, it is an aim of the present invention to provide apparatus for carrying out the new method.

The present inventors have addressed the above need in fact by providing two new methods, as well as apparatus for carrying out the new methods.

Accordingly a first aspect of the present invention provides a method for disinfecting vegetable material, said method comprising the steps of (i) providing a vegetable material as a suspension in a fluid, (ii) flowing the suspended vegetable material along an axis and irradiating substantially all of the surface of the suspended vegetable material with UV-C radiation from a UV-C light source so that substantially all of the surface is disinfected, characterized in that the UV-C light source comprises an array of UV-C lamps disposed about the axis to irradiate the axis during use.

Furthermore, the first aspect of the present invention provides apparatus for disinfecting vegetable material suspended in a fluid, comprising an inlet port for introduction of the vegetable material into the apparatus, a UV-C light source for irradiating substantially all of the surface of the vegetable material during use, first means for flowing the suspension along an axis and an outlet port for delivering the vegetable material to the outside of the apparatus, characterized in that the UV-C light source comprises an array of UV-C lamps disposed about the axis.

The first aspect of the present invention also provides the use of an array of UV-C lamps disposed about a central axis for the purpose of disinfecting a suspension of vegetable material.

In addition, a second aspect of the present invention provides a method for disinfecting a plant leaf, plant stem, or part thereof, said method comprising the steps of: (i) providing a plant leaf, plant stem, or part thereof; (ii) in a first zone causing stomata to open on the plant leaf, plant stem or part thereof using a stomata opening agent) and (iii) in a second zone treating the plant leaf, plant stem or part thereof from step (ii) with a disinfectant whilst the stomata opened in step (ii) remain open.

The second aspect of the present invention also provides apparatus for disinfecting a plant leaf, plant stem or part thereof comprising an inlet port for introduction of the plant leaf, plant stem or part thereof into the apparatus; means for exposing the plant leaf, plant stem or part thereof to a stomata opening agent) means for treating the plant leaf, plant stem or part thereof with at least one disinfectant after exposure to the stomata opening agent and an outlet port for delivering the disinfected plant leaf, plant stem or part thereof to the outside of the apparatus.

The second aspect of the present invention further provides the use of a disinfectant for the purpose of disinfecting the open stomata of a plant leaf, plant stem or part thereof. Furthermore, the second aspect of the present invention provides the use of a stomata opening agent in a method for disinfecting a plant leaf, plant stem or part thereof.

Referring to the first aspect of the present invention, the term "vegetable material" can be taken to include fruits, vegetables, other plant leaves, other plant stems or parts thereof. The term "vegetable" includes all parts of a vegetable plant that are edible, for example, roots, tubers, and bulbs, as well as leaves and stems. The vegetable material may be fresh or individually quick frozen.

In the method according to the first aspect of the present invention, substantially all of the surface of the vegetable material is irradiated with UV-C radiation. Thus, substantially all of the surface of the vegetable material is disinfected effectively. This has been achievable in the present method only by providing the vegetable material as a suspension in a fluid. The method provides a process for disinfecting vegetable material such as herbs and salad vegetables for use in chilled food products that provides an excellent microbiocidal action, and therefore reduces the possibility of the herbs or salad vegetables being the cause of a food poisoning outbreak.

The method according to the first aspect of the present invention can result in a 3-log kill of bacteria or higher.

UV-C irradiation will also kill viruses, yeasts and moulds.

In step (ii) the suspended vegetable material is flowed along an axis and is irradiated by a UV-C light source. The suspension may be flowed using a pump selected from the group consisting of double diaphragm pumps, sign pumps and lobe pumps. A double diaphragm pump is preferred because it causes the least damage to the suspended vegetable material.

Also, double diaphragm pumps are the most hygienic for operation and cleaning and are operated pneumatically which suits a wet environment.

The UV-C light source comprises an array of UV-C lamps disposed about the axis to irradiate the axis during use.

This arrangement maximises the irradiation of the surface of the vegetable material by the UV-radiation.

Important criteria for disinfection using UV-C radiation are the intensity of radiation and the irradiation dose necessary to kill the relevant microorganisms. Knowing the irradiation dose necessary to kill the relevant microorganism, with a fixed value of the intensity of radiation, the skilled person will be able to determine the necessary period of irradiation. Each lamp in the array of lamps preferably radiates at an intensity of from 0.032 to 0.040 W/cm2. Suitable equipment is available from companies that manufacture systems for the disinfection of water and other liquids, which typically provide ultra-violet irradiation in the range of 240 to 280 nm wavelength at an intensity of about 0.032 to 0.040 W/cm2.

Preferably, in order to maximise the exposure of substantially all of the surface of the suspended vegetable material to the UV-C radiation, where the suspended vegetable material is flowed along an axis, the flow is nonlaminar. Thus, preferably, the flow of the vegetable material in suspension is turbulent as it passes through the irradiation equipment. If necessary, vanes can be incorporated into the circuit to ensure that the flow is sufficient turbulent. An optional step in the method according to the first aspect of the present invention is a step of increasing the turbulence of the flow.

Preferably, step (i) comprises the step of introducing the vegetable material through an inlet port and closing the inlet port after introduction. Usually, the vegetable material would not be introduced already in suspension.

The flow rate also has to be controlled so that the vegetable material receives an adequate amount of ultra- violet irradiation in order to disinfect them; in practice this is best done by recirculating the vegetable material through the irradiation equipment for a suitable number of passes. Thus, it is envisaged that step (i) will comprise irradiating the suspended vegetable material with UV-C radiation for a first time and then irradiating the suspended vegetable material with UV-C radiation again. In this regard, irradiation of the suspended vegetable material with UV-C radiation may be repeated for up to 40 times, typically 10 to 30 times.

Preferably, the UV-C radiation has a wavelength in the range 240 am to 280 nm. Radiation having a wavelength in this range has been found to be most effective in disinfecting

vegetable materials.

Referring to the suspension of the vegetable material in a fluid, it is preferred that the vegetable material is suspended in an aqueous solution. This has the advantage that it is possible to dissolve disinfectants in the solution. Accordingly, where the vegetable material is suspended in an aqueous solution, it is preferred that the solution contains a disinfectant. It is envisaged that in this case the treatment of the vegetable material by the disinfectant in the solution will be continuous throughout the method. In other words, the treatment zone would cover the entire fluid path of the suspension.

The combination of the use of a disinfecting solution and UV-C radiation provides a synegestic effect in terms of microbiocidal action. The combination of microbiocidal ultra-violet irradiation and use of a disinfecting solution gives a synergistic microbiocidal effect that can result in a 4 or 5-log kill of bacteria. This combination also has the advantage that mould spores or protozoan pathogens such as Cryptosporidium, which are relatively resistant to UV-C radiation, may be killed by the disinfectant, particularly if it is ozone. The kill resulting from the combined treatment is adequate to ensure that the loading of pathogenic micro-organisms is sufficiently reduced to ensure the safety of the product. It can also extend the possible shelf-life by up to a day, which is significant in terms of the short shelf-life that these products normally have.

Where a further disinfectant is used in combination with UV- C radiation, the present method has the advantage that the further disinfectant may be used at a lower concentration than would otherwise be effective. This has the advantage particularly with disinfectants such as vinegar or chlorine where the product may otherwise have had a disinfectant taste.

The disinfectant used may be a solution of any suitable disinfecting agent that has the required microbiocidal effect and is safe and legally allowed for use in vegetable material. Examples of known disinfecting agents are solutions of ozone, hypochlorites (particularly sodium hypochlorite), chlorine dioxide, hydrogen peroxide, organic acids including acetic acid or vinegar, and peroxyacids such as peracetic acid. There are also various proprietary solutions available for decontaminating vegetable material such as herbs and salad vegetables. Suitable ranges of concentration for using the disinfectant chemicals will be well-known to the skilled person, but the following ranges can be given as examples: (a) 0.1 to 40 parts per million of ozone, preferably about 1 part per million of ozone; (b) 20 to 200 parts per million of available chlorine for a sodium hypochlorite solution, preferably around 100 parts per million of available chlorine; (c) 1 to 5 parts per million of chlorine dioxide; (d) 1 to 13% of acetic acid, either as an acetic acid solution or as vinegar (diluted or neat); (e) 90 parts per million of peracetic acid; or (f) 2 to 5% hydrogen peroxide.

It should be noted that the use of chlorinated water is not allowed in some jurisdictions for organic vegetable material. Furthermore, alternatives are being sought to the use of chlorinated water alone in the decontamination of non-organic vegetable material because chlorine is rapidly inactivated by reaction with organic compounds and the reaction products are suspected of being toxic. The use of a solution of ozone in water as the disinfecting agent certainly will overcome these problems and, thus, is preferred.

Optionally, the method of the first aspect of the present invention includes a step of causing stomata to open on any plant leaf, plant stem or part thereof comprised in the vegetable material. This step may be carried out as described in the second aspect of the present invention.

Referring to the method of the second aspect of the present invention, the present inventors have identified that one problem to be considered in disinfecting plant leaves, stems and parts thereof, particularly herbs and salad vegetables is that the contaminating spoilage organisms or pathogens can be distributed over several types of locations in or on the plant leaves, stems and parts thereof. They may be: (a) on the external surface of the leaves or other parts used, or (b) within the stomata of the leaves, or (c) either within the- cells or between the cells in the structure of the leaves or other parts used.

Having identified these sources of contamination, ideally, a decontamination treatment should address at least two of these locations if not all three, in order to provide a long shelf-life without spoilage and to avoid the risk of food poisoning.

A further problem to be considered is the fact that different spoilage organisms or pathogens may accumulate preferentially in different locations, and they may be more or less firmly attached to the plant leaves, stems and parts thereof, causing greater or lesser difficulty in removing them.

Having identified these problems, the present inventors developed the method according to the second aspect of the present invention in order to at least partially address these problems.

Preferably, in the method according to the second aspect of the present invention, step (i) comprises the step of introducing the plant leaf, plant stem or part thereof into the first zone via an inlet port and closing the inlet port

after introduction.

It is envisaged that the plant leaf, plant stem or part thereof, will be moved through the first zone and the second zone in a continuous manner. Furthermore, it is envisaged that usually treatment in step (ii) will be continuous. In this case, where the plant leaf, plant stem or part thereof is in suspension in a fluid, the first zone may cover the entire fluid path of the suspension. Nevertheless, the possibility of the method further comprising a step (iv) of repeating the step of causing stomata on the plant leaf, plant stem or part thereof to open using a stomata opening agent is not excluded.

Suitable stomata opening agents may include UV-A radiation, metal chlorides and ozone. Preferred stomata opening agents are potassium chloride and ozone. Typically, these stomata opening agents will be provided as a solution into which the plant leaf, plant stem or part thereof is placed. Suitable times of exposure to the stomata opening agent in step (ii) are in the range 10 minutes to 60 minutes. Having selected a stomata opening agent, the skilled person will be able to optimise the dosage or concentration and exposure time for a given plant species.

The disinfectant may be any suitable disinfectant that has the required microbiocidal effect and is safe and legally allowed for use in disinfecting plant leaves, plant stems and parts thereof. Examples of known disinfectants include organic acids including acetic acid or vinegar, peroxyacids such as peracetic acid; hypochlorites (particularly sodium hypochlorite); chlorine dioxide; UV-C radiation; ozone, and hydrogen peroxide. Apart from UV-C radiation, these disinfectants typically would be provided as a solution.

Suitable ranges for concentrations for these solutions are as described above in relation to the method of the first aspect of the present invention.

The preferred disinfectant is UV-C radiation and step (iii) preferably comprises irradiating substantially all of the surface of the plant leaf, plant stem or part thereof with UV-C radiation. Typically, in step (iii) the plant leaf, plant stem or part thereof is moved along an axis and is irradiated by a UV-C light source. Preferably, the UV-C light source comprises an array of lamps disposed about the axis. This arrangement maximises the irradiation of the surface of the plant leaf, plant stem or part thereof by the UV-radiation.

Where the disinfectant is UV-C radiation, preferably, the method comprises irradiating substantially all of the surface of the plant leaf, plant stem or part thereof with UV-C radiation for a first time and repeating the irradiation of substantially of the surface of the plant leaf, plant stem or part thereof with UV-C radiation again for up to 40 times, preferably 10 to 30 times.

Typically, each lamp in the array of lamps radiates at an intensity of from 0.032 to 0.040 W/cm2.

Preferably, the UV-C radiation has a wavelength in the range of 240 nm to 280 nm. Radiation having a wavelength in this range has been found to be particularly effective at disinfecting the plant leaves, plant stems and parts thereof.

In the method according to the second aspect of the present invention, the second zone may comprise the first zone or the first zone may comprises the second zone so at least a part of step (ii) and step (iii) are carried out simultaneously.

Preferably, the plant leaf, plant stem or part thereof is in suspension in a fluid. This is particularly advantageous where the fluid is an aqueous solution because this allows the stomata opening agent and/or a disinfectant to be dissolved into the solution for continuous treatment of the plant leaf, plant stem or part thereof. In this regard, where the disinfectant in step (iii) is UV-C radiation, the solution may contain a further disinfectant. This further disinfectant may be selected from the group consisting of organic acids including acetic acid or vinegar, peroxyacids such as peracetic acid, hypochlorites (particularly sodium hypochlorite), chlorine dioxide, ozone, and hydrogen peroxide.

Where the plant leaf, plant stem or part thereof is in suspension in a fluid, typically, the suspension is flowed through the first and the second zone. The suspension may be caused to flow using a pump selected from the group consisting of double diaphragm pumps, sign pumps and lobe pumps. The preferred pump is a double diaphragm pump because it causes the least damage to the suspended vegetable material. Also, double diaphragm pumps are the most hygienic for operation and cleaning and are operated pneumatically which suits a wet environment.

In order to improve the effectiveness of the method, particularly, where the disinfectant is UV-C radiation, it is preferred that the flow is non laminar. In this regard, the method according to the second aspect of the present invention may comprise a step of increasing the turbulence of the flow.

In the method according to the first or the second aspect of the present invention, the suspension preferably is made by providing vegetable material, plant leaf, plant stem or part thereof at a ratio of 1 to 10 kg of vegetable material, plant leaf, plant stem or part thereof to 50 to 100 litres of fluid. More preferably, the suspension is made by providing vegetable material, plant leaf, plant stem or part thereof at a ratio of about 5kg vegetable material, plant leaf, plant stem or part thereof to 95 litres of fluid. The vegetable material, plant leaf, plant stem or part thereof preferably is provided as pieces each having a volume of up to 25 mm3.

Furthermore, in the method according to either the first aspect or the second aspect of the present invention, the method may further comprise a step of cutting the vegetable material, plant leaf, plant stem or part thereof at any suitable stage in the method.

The present invention also provides a disinfected vegetable material, plant leaf, plant stem or part thereof obtained by or obtainable by the method according to either the first aspect or the second aspect of the present invention. The disinfected product may be characterized by low microbial levels and the lack of disinfectant taste.

Referring to the apparatus according to either the first or second aspect of the present invention, an advantage of these is that they are as easily cleanable, indeed they are almost suitable for the use of cleaningin-place techniques.

The apparatus according to the first aspect or the second aspect of the present invention also has the advantage that it has an outlet port for delivering the vegetable material to the outside of the apparatus. Typically, the vegetable material will be in suspension.

In the apparatus according to the first aspect of the present invention, the UV-C light source comprises an array of UV-C lamps disposed about an axis. As mentioned above this arrangement maximises the irradiation of the surface of the vegetable material by the UV-radiation.

Preferably, the first means for flowing the suspension comprises a first conduit having a first location and a second location disposed along the axis and means for flowing the suspension from the first location to the second location along the axis. More preferably, the apparatus further comprises second means for flowing the suspension from the second location to the first location. The second means may comprise a second conduit.

The first and/or second means may include a pump as described above in relation to the methods of either the first or second aspects of the present invention.

The apparatus according to the first aspect of the present invention also may include means for exposing the vegetable material to a further disinfectant. The means may comprise a vessel into which the vegetable material and the further disinfectant can be introduced.

Referring to the apparatus according to the second aspect of the present invention, preferably, the means for exposing the plant leaf, plant stem or part thereof to a stomata opening agent comprises a vessel into which the plant leaf, plant stem or part thereof and the stomata opening agent can be introduced. Alternatively, the means for exposing the plant leaf, plant stem or part thereof to a stomata opening agent may comprise a UV-A light source for irradiating substantially all of the surface of the plant leaf, plant stem or part thereof during use.

The means for treating the plant leaf, plant stem or part thereof with at least one disinfectant may comprise a vessel into which the plant leaf, plant stem or part thereof and the at least one disinfectant can be introduced. This vessel may be the same or different from the vessel into which the plant leaf, plant stem or part thereof and the stomata opening agent may be introduced.

Alternatively, the means for treating the plant leaf, plant stem or part thereof with at least one disinfectant may comprise a UV-C light source for irradiating substantially all of the surface of the plant leaf, plant stem or part thereof during use. As mentioned above in relation to the method of the first and second aspect of the present invention, it is preferred that the UV-C light source comprises an array of UV-C lamps disposed about an axis.

The means according to the second aspect of the present invention for treating the plant leaf, plant stem or part thereof may comprise a first conduit having a first location and a second location disposed along the axis and means for moving or flowing the plant leaf, plant stem or part thereof from the first location to the second location along the axis. In this regard, preferably, the apparatus further comprises second means for moving or flowing the plant leaf, plant stem or part thereof from the second location to the first location. Preferably, this second means is a second conduit.

Again, as for the apparatus according to the first aspect of the present invention, the first and/or second means may include a pump as described in relation to the method according to the first or second aspects of the present invention above.

In the apparatus according to either the first aspect or the second aspect of the present invention, it is preferred that the inlet port is closable with respect to the outside of the apparatus such that when the inlet port is closed the inside of the apparatus either is closed with respect to the outside of the apparatus or is open to the outside of the apparatus only via the outlet port. Advantageously, this allows the process to take place in the "low risk area" of a food factory in an enclosed system with the disinfected vegetable material, plant leaves, plant stems and parts thereof being piped through a wall into the "high risk area" of the factory via the outlet port for use in the production of the chilled foods for which they are required. The process is ideally a batch process in an enclosed system that eliminates the risk of recontamination of the vegetable material, plant leaves, stems and parts thereof after they have been disinfected.

Also in the apparatus according to the first aspect or the second aspect of the present invention, a cutting device may be included at any suitable location for cutting the vegetable material, plant leaf, plant stem or part thereof.

Thus, optionally, the vegetable material, plant leaf, plant stem or partthereof may be chopped for use by means of an inline cutter while circulating in the treatment apparatus.

The apparatus according to either the first aspect or the second aspect of the present invention may further include a chamber or hopper in communication with the inlet port. The chamber may be the same or different from the vessel into which the plant leaf, plant stem or part thereof and the stomata opening agent can be introduced and/or the vessel into which the vegetable material, plant leaf, plant stem or part thereof and a disinfectant can be introduced.

Also in either the first or second apparatus according to the present invention, the apparatus may include a valve having at least three openings where one opening is in communication with the outlet ports and the valve is capable either of opening the inside of the apparatus to the outside of the apparatus or of closing the inside of the apparatus from the outside of the apparatus. Such a valve enables the vegetable material, plant leaf, plant stem or part thereof either to be directed to the outside of the apparatus via the outlet port or to be directed to recirculate around the inside of the apparatus.

Finally, to avoid clumping of the vegetable material, plant leaves, plant stems or parts thereof, a device - for separating the vegetable material, plant leaves, plant stems or parts thereof from other vegetable material, plant leaves, plant stems or parts thereof may be included in the apparatus according to either the first aspect or the second aspect of the present invention. Preferably, the device- avoids clumping of the vegetable material, plant leaves, plant stems or parts thereof during the formation of the suspension. In this case, the device may be provided, for example, at the point where the vegetable material, plant leaves, plant stems or parts thereof is introduced into- the apparatus.

The present invention now will be described in further detail with reference to the accompanying drawings in which: Figure 1 shows preferred apparatus according to the first or second aspect of the present invention from the side.

Figure 2 shows the same preferred apparatus according to the first or second aspect of the present invention from the front.

In Figures 1 and 2, (a) is a grid for separating clumps; (b) is a chamber or hopper in communication with the inlet port; (c) is a conduit) (d) is a pumps (e) is a further conduit leading to a further conduit (h); (g) is a UV-C light source. At least a part of conduits (e) and (h) are along an axis about which the UV-C light source is disposed) (i) is a three way valve; (k) is a conduit leading to the outlet port, and (f) is a timer control system.

Description of one preferred process

Broadly, the present invention includes a process for treating herbs and salad vegetables comprising the steps of: (a) optionally subjecting the herbs or salad vegetables to a process that causes stomata (typically on the leaves) to open, then (b) washing the herbs or salad vegetables in a disinfecting solution, comprising any suitable disinfectant that is allowed for such use, and (c) subjecting the herbs or salad vegetables to microbiocidal ultra- violet irradiation while they are circulating in suspension in the disinfecting solution.

The vegetable material such as herbs or salad vegetables are first placed in a hopper, where they may be subjected to the stomata-opening treatment. They may be added as fresh herbs or salad vegetable pieces of up to 25 mm3 in volume, or as IQF (individually quick frozen) herbs. If they are fresh herbs or salad vegetables straight from the field, then they will need to be rinsed to remove surface dirt before they are placed in the system. If this is not done then the dirt will enter the system, where it may inactivate to some extent the disinfecting solution. A grating over the hopper may be incorporated to break up any clumps, especially of IQF herbs. Advantageously, the stomata-opening treatment is carried out by irradiating the herbs or salad vegetables with UV-A irradiation, while they are circulating the hopper in suspension in water.

After the optional stomata-opening treatment is completed, the disinfecting solution is added into the hopper at sufficient concentration so that when diluted with the water already present, it will give the required microbiocidal effect. Alternatively, the disinfecting chemicals are added as solids and dissolved in the water present by circulation through the system. It is important that the final ratio of disinfecting solution to herbs or salad vegetables is in the range of 50 to 100 litres of solution to 1 to 10 kg of herbs or salad vegetables, preferably about 95 litres of solution to 5 kg of herbs or salad vegetables. This is to ensure that the concentration of herbs or salad vegetables in the disinfecting solution is low enough to ensure that all the surfaces of all the particles of herbs or salad vegetables receive sufficient ultra-violet irradiation to give the required microbiocidal effect, and that shadowing is minimised. The mixture of herbs or salad vegetables and disinfectant solution is then pumped from the hopper, using a suitable type of pump that will not damage the herbs or salad vegetables, such as a double diaphragm pump, through a standard apparatus for the ultra-violet irradiation of liquids, such as those made by Hanovia Ltd or Wedeco UV Systems plc.

Optionally, after the herbs or salad vegetables have been irradiated with ultra-violet light for a sufficient period of time, the mixture of herbs or salad vegetables and disinfecting solution may be directed on to an inline cutter to be chopped. This can be in the form of a cheese- knife, that is, a rectangular grid of sharp blades placed in the pipeline so that the blades are in line with the direction of flow of the mixture of herbs or salad vegetables and disinfecting solution. The herbs or salad vegetables are forced by the flow of the mixture against the blades and are cut to the desired size, which is regulated by the spacing of the blades in the rectangular grid.

Alternatively the in-line cutter can be an Urschel_-type cutter, with a revolving blade that is driven by the flow of the mixture of herbs or salad vegetables and disinfecting solution acting on a paddle attached to the blade. It may be necessary to recirculate the mixture of herbs or salad vegetables and disinfecting solution through the in-line cutter to ensure that the herbs or salad vegetables have been chopped to the desired size.

The disinfected herbs or salad vegetables, whether chopped or not, are now ready for use, and can be piped to a "high risk area" where they can be separated from the disinfecting solution, for example by filtering, and used in the preparation of food products. If they are not required for immediate use they can be recirculated back to the hopper or through the treatment system.

Description of the preferred apparatus

The equipment for the treatment of vegetable material such as herbs and salad vegetables comprises the following elements (with reference to the attached figures); (a) A grid for breaking up any clumps of herbs or salad vegetables. This is particularly useful if the herbs or salad vegetables have been individually quick frozen.

(b) A hopper where the herbs or salad vegetables can be suspended in water or in disinfecting solution.

Ideally the hopper has an inlet port that is interlocked so that it cannot be opened after the treatment of the herbs or salad vegetables has begun until the treatment has been completed and the herbs or salad vegetables have been discharged from the system. This will prevent any contamination of the disinfected herbs or salad

vegetables by the introduction of contaminated

material. It will also ensure the safety of the operators if the disinfecting solution is a solution of ozone in water. If the treatment incorporates the optional stomata-opening process, then this can be advantageously carried out by means of an ultra-violet (UV-A) lamp installed on the under-surface of the lid, which irradiates the herbs or salad vegetables in suspension as they are circulated through the equipment and back into the hopper. Alternatively, this can be carried out by the generation of ozone in the hopper by means of an ozone- generating system, or by the addition of a solution of potassium chloride.

Similarly, the disinfecting solution can be added to the herbs or salad vegetables in the hopper, either as a made-up solution, or as solid chemicals, or if the disinfecting agent is ozone, by generating it in the hopper by means of an ozone-generating system.

(c) A pipe from the hopper to the pump.

(d) A pump for circulating the suspension of herbs or salad vegetables in water (for stomata-opening purposes) or in disinfecting solution (for treatment purposes) through the equipment. The pump is preferably a double diaphragm pump though other types of pump such as those previously mentioned are also suitable for use.

(e) A pipe from the pump to the ultra-violet irradiation system. This pipe may optionally contain vanes to ensure that the flow of the suspension trough the ultra-violet irradiation system is sufficient turbulent to ensure that all surfaces of the particles of the herbs or salad vegetables are irradiated.

(f) A timer control system mounted on the pipe to ensure that the suspension of herbs or salad vegetables is circulated through the ultraviolet irradiation system for the required number of passes to ensure the maximum effective rate of disinfection.

(g) A standard ultra-violet irradiation system for irradiating liquids with UV-C irradiation. Such systems are available from manufactures such as Hanovia Ltd and Wedeco UV Systems plc. They may suitably consist of a number of ultra-violet lamps mounted longitudinally around a quartz tube through which the suspension of herbs or salad vegetables is circulated, or of a single ultra- violet lamp mounted longitudinally in a quartz tube in a chamber through which the suspension of herbs or salad vegetables is circulated. These are standard configurations for the irradiation of liquids, but any other configuration that ensured sufficient irradiation of the surfaces of the particles of the herbs or salad vegetables could be used.

(h) A pipe from the ultra-violet irradiation system to a three-way valve.

(i) A three-way valve that directs the suspension of herbs or salad vegetables in disinfecting solution back to the hopper for recirculation through the equipment, or, when the treatment is complete, directs the suspension to the discharge pipe.

(j) A pipe from the three-way valve back to the hopper.

(k) A discharge pipe from the three-way valve to the site of use of a disinfected herbs or salad vegetables. This may advantageously be in a "high-risk area" of the factory, so that the herbs or salad vegetables are treated in the "low-risk area" and are only directed into the "high- risk area" when they have been disinfected.

An inline cutter can be fitted at any convenient point into the system.

Claims

CLAIMS: 1. A method for disinfecting a plant leaf, plant stem, or part

thereof, said method comprises the steps of: (i) providing a plant leaf, plant stem, or part thereof; (ii) in a first zone causing stomata to open on the plant leaf, plant stem or part thereof using a stomata opening agent; and (iii) in a second zone treating the plant leaf, plant stem or part thereof from step (ii) with a disinfectant whilst the stomata opened in step (ii) remain open.
2. A method according to claim 1, wherein step (i) comprises the step of introducing the plant leaf, plant stem or part thereof into the first zone via an inlet port and

closing the inlet port after introduction.
3. A method according to claim 1 or 2, wherein the plant leaf, plant stem or part thereof is moved through the first zone and the second zone in a continuous manner.
4. A method according to any one of claims 1 to 3, wherein the stomata opening agent is selected from the group consisting of potassium chloride and ozone.
5. A method according to any one of claims 1 to 4, wherein the time of exposure to the stomata opening agent in step (ii) is in the range 10 to 60 minutes.
6. A method according to any one of claims 1 to 5, wherein the second zone comprises the first zone or the first zone comprises the second zone so that at least a part of step (ii) and step (iii) are carried out simultaneously.
7. A method according to any one of claims 1 to 6, wherein the plant leaf, plant stem or part thereof is in suspension in a fluid.
8. A method according to claim 7, wherein the suspension is flowed through the first zone and the second zone.
9. A method according to claim 8, wherein the suspension is caused to flow using a pump selected from the group consisting of double diaphragm pumps, sine pumps, and lobe pumps.
10. A method according to claim 9, wherein the pump is a double diaphragm pump.
11. A method according to any one of claims 8 to 10, wherein the flow is non-laminar.
12. A method according to claim 11 further comprising a step of increasing the turbulence of the flow.
13. A method according to any one of claims 7 to 12, wherein the fluid is an aqueous solution.
14. A method according to any one of claims 7 to 13, wherein the disinfectant is selected from the group consisting of organic acid, vinegar, hypochlorite, chlorine dioxide, W -C radiation, ozone, peroxy acid, and hydrogen peroxide.
15. A method according to claim 14, wherein the disinfectant is W -C radiation and step (iii) comprises irradiating substantially all of the surface of the plant leaf, plant stem or part thereof with W -C radiation.
16. A method according to claim 15, comprising irradiating substantially all of the surface of the plant leaf, plant stem or part thereof with W-C radiation for a first time and repeating the irradiation of substantially all of the surface of the plant leaf, plant stem or part thereof with W C radiation for up to 40 times.
17. A method according to claim 15 or claim 16, wherein in step (iii) the plant leaf, plant stem or part thereof is moved along an axis and is irradiated by a W -C light source.
18. A method according to claim 17, wherein the W -C light source comprises an array of lamps disposed about the axis.
19. A method according to claim 18, wherein each lamp in the array of lamps radiates at an intensity of from 0.032 to 0.040 W/cm2.
20. A method according to any one of claims 15 to 19, wherein the W -C radiation has a wavelength in the range 240 nm to 280 nm.
21. A method according to claims 13 to 20, wherein the fluid is an aqueous solution and the solution contains a further disinfectant.
22. A method according to claim 21, wherein the further disinfectant is selected from the group consisting of organic acid, vinegar, hypochlorite, chlorine dioxide, ozone, peroxy acid, and hydrogen peroxide.
23. A method according to any one of claims 7 to 22, wherein the suspension is made by providing plant leaf, plant stem or part thereof at a ratio of 1 to 10 kg, plant leaf, plant stem or part thereof to 50 to 100 litres of fluid.
24. A method according to any one of the preceding claims further comprising a step of cutting the plant leaf, plant stem, or part thereof.
25. A method according to any one of the preceding claims, wherein the plant leaf or plant stem comprises a herb leaf or herb stem.
26. A method according to any one of the preceding claims, wherein the plant leaf, plant stem, or part thereof is provided as pieces each having a volume of up to 25 mm3.
27. A disinfected plant leaf, plant stem or part thereof obtained by the method of any one of the preceding claims.
28. Apparatus for disinfecting a plant leaf, plant stem or part thereof comprising: an inlet port for introduction of the plant leaf, plant stem or part thereof into the apparatus; means for exposing the plant leaf, plant stem or part thereof to a stomata opening agent; means for treating the plant leaf, plant stem or part thereof with at least one disinfectant after exposure to the stomata opening agent; and an outlet port for delivering the disinfected plant leaf, plant stem or part thereof to the outside of the apparatus.
29. Apparatus according to claim 28, wherein the means for exposing the plant leaf, plant stem or part thereof to a stomata opening agent comprises a vessel into which the plant leaf, plant stem or part thereof and the stomata opening agent can be introduced.
30. Apparatus according to claim 28 or claim 29, wherein the means for treating the plant leaf, plant stem or part thereof with at least one disinfectant comprises a vessel into which the plant leaf, plant stem or part thereof and the at least one disinfectant can he introduced.
31. Apparatus according to claim 28 or claim 29, wherein the means for treating the plant leaf, plant stem or part thereof with at least one disinfectant comprises a W -C light source for irradiating substantially all of the surface of the plant leaf, plant stem or part thereof during use.
32. Apparatus according to claim 31, wherein the W -C light source comprises an array of W-C lamps disposed about an axis.
33. Apparatus according to claim 31 or claim 32, wherein the means for treating the plant leaf, plant stem or part thereof comprises a first conduit having a first location and a second location disposed along the axis and means for moving the plant leaf, plant stem or part thereof from the first location to the second location along the axis.
34. Apparatus according to claim 33, further comprising second means for moving the plant leaf, plant stem or part thereof from the second location to the first location.
35. Apparatus according to claim 33 or claim 34, wherein the first and/or second means includes a pump selected from the group consisting of double diaphragm pumps, sine pumps, and lobe pumps.
36. Apparatus according to claim 35, wherein the pump is a double diaphragm pump.
37. Apparatus according to any one of claims 28 to 36, wherein the inlet port is closable with respect to the outside of the apparatus such that when the inlet port is closed the inside of the apparatus either is closed with respect to the outside of the apparatus or is open to the outside of the apparatus only via the outlet port.
38. Apparatus according to any one of claims 28 to 37 further including a cutting device for cutting the plant leaf, plant stem or part thereof.
39. Apparatus according to any one of claims 28 to 38, further including a chamber in communication with the inlet port.
40. Apparatus according to any one of claims 28 to 39, including a valve having at least three openings, where one opening is in communication with the outlet port and the valve is capable either of opening the inside of the apparatus to the outside of the apparatus or of closing the inside of the apparatus from the outside of the apparatus.
41. Apparatus according to any one of claims 28 to 40 further including a device for separating plant leaves, plant stems or parts thereof from other plant leaves, plant stems or parts thereof.