The present invention relates to the treatment of fresh produce post - harvesting, in particular to the treatment of cut plant material. Herbs are available for sale in dried form (that is, desiccated form) or in fresh form. Fresh herbs are typically cut in the field, chilled, transported and then packed into plastic film or bags, prior to stocking in a retail environment. Cut salad leaves, baby leaves and spinach are most commonly available for sale in fresh form in a washed or an unwashed state. Like fresh herbs, the leaves are typically cut in the field or glasshouse, chilled, transported and then packed into plastic film or bags, prior to stocking in a retail environment. It is often found that this sequence of events results in partial dehydration of the fresh cut plant leaves, due to the low water vapour pressure in the external environment to which they are exposed. As a result, the consumer of, in particular, unwashed leaves may perceive a reduction in freshness of the leaves. Washed salad leaves aim for a tenfold (1 log) reduction in microbes, but often suffer a reduced shelf life due to the processing steps that the leaves undergo.

Therefore, it is desirable to increase the quality of unwashed fresh leaves at the point of consumption, in particular to reduce the extent of dehydration occurring during processing of the cut product and offering a degree of sanitisation of the products.

According to a first aspect of the present invention there is provided a method of treating cut plant material, comprising the steps of

• providing a quantity of cut plant material;

· exposing the plant material to an atmosphere of a fog comprising sanitised water droplets at a temperature in the range of 10-30°C; • wherein the atmosphere of a fog of sanitised water droplets is urged towards the cut plant material at a rate of 5 to 10 m/s.

It is thought that this treatment causes sanitised, electrically activated (charged) water droplets (fog) to condense on the surface of the plant material and enter the plant material through stomata (typically around 10μηι diameter), thus helping to prevent dehydration of the plant material and generally improve freshness. The electrically charged and activated fog has a sanitising effect. Before treatment, the plant material is stored at a temperature lower than 30°C. For example, it may be held in cold storage at a temperature of around 5°C. The yield of the plant material (that is, the weight of material that is e.g. sold to a consumer) is also increased, due to water being adsorbed or absorbed by the plant material, typically between 2.5% and 7.5%. This has the benefit of increasing the surface moisture on the fresh leaves. The surface moisture and plumpness or turgidity of the leaves give an impression of freshness that the consumer appreciates visually and with other senses, so improving the perceived quality of the fresh leaves. Further, the REDOX potential of 1 100 - 1 150mV of the electrically activated water (including free chlorine at 30-80ppm) reduces the microbes on the leaves, improving consumer safety and affecting shelf life. The use of the fog is most effective with just sanitised water droplets, i.e. fresh. The REDOX potential and chlorine decline with time. The volume of the fog delivered can determine the sanitising effect.

It is known (for example, from US2002/0184897) to heat shock produce (e.g. lettuce) by immersing it into warm water (e.g. at 50°C). However, it is considered that this process leaves excessive residual water on the produce, which may accelerate the process of deterioration and/or deplete any aromatic oils present at the surface of the produce. Thus, the present invention avoids the problems inherent in known immersion processes.

Furthermore, the present invention does not require drying of the produce, and thus allows significant mechanical damage to the plant material to be avoided. In an embodiment of the method of the first aspect of the invention the fog of sanitising water droplets is urged towards the cut plant material through a plurality of circular openings providing at least one column of fog to impinge on the cut plant material. In another embodiment of the method the fog of sanitising water droplets is urged towards the cut plant material through a plurality of slit shaped openings providing at least one ribbon of fog to impinge on the cut plant material. In an embodiment the fog of sanitising water droplets is directed towards the leaf surface via one or more plenum chambers. More preferably via four plenum boxes.

In an embodiment the fog of sanitised water droplets is directed to the surface of the cut plant material. The impinging of the fog directly onto the leaf surface is thought to improve uptake of moisture by the leaf. This means that a measureable rehydration effect can be achieved more quickly than by merely exposing or conveying the cut plant material to the atmosphere of the fog.

Preferably, the temperature of the plant material prior to exposure to the fog or humid atmosphere is less than 10°C, more preferably less than 8°C. It is thought that the temperature differential between the temperature of the plant material and the temperature of the humid fog atmosphere helps to promote condensation of water vapour onto the plant material.

Preferably, the temperature of the plant material prior to exposure to the humid atmosphere is greater than 3°C.

In view of the reaction and treatment of plant material described above, the method of the first aspect of the invention is typically applied to cut herbs, baby leaves, spinach, salad leaves.

Preferably, the humidity is greater than 90%, more preferably greater than 95%. A relative humidity of close to 100% is most desirable for uptake of moisture by the leaves. Preferably, the exposure time is greater than 0.5 minutes. In general, the exposure time is less than 5 minutes, preferably less than 3 minutes, more preferably less than 2.25 minutes. However, a sufficient dwell time or exposure time can be in the range of 1 to 2 minutes. The volume of fog is important in reducing the microbial loadings on the leaves and a suitable time period for producing sufficient fog in an embodiment is between 1 to 2 minutes.

Typically, the humid atmosphere is provided by passing water over an evaporator or vaporiser. In general, the water is purified (for example through reverse osmosis) and/or sterilised (for example through UV filtration) before being passed over the evaporator or vaporiser, although this may not always be necessary.

Some results have shown a beneficial reduction in the microbes on leaf material processed with the use of electrolysed water from reverse osmosis. The sanitised water microdroplets of the fog atmosphere of an embodiment have a diameter in the range from 3 to 10 microns. The term droplet in this application includes microdroplets.

In order to avoid a reduction in the quality of some treated plant material, it is generally desirable that the plant material should be wrapped in an impervious package within two minutes (preferably 1.5 minutes) after being exposed to the humid atmosphere.

Typically, the humid atmosphere is contained within a reactor vessel (the reactor vessel is typically insulated to help maintain the temperature and humidity within the vessel). In general, conveying means are provided to convey the plant material from an entrance to an exit of the reactor vessel. In order to expose the plant material to the humid atmosphere for a sufficient time, while maintaining the size of the reaction vessel at practical and acceptable levels, and ensuring that the required processing rates are achieved, the plant material may be provided as a plurality of portions that travel through the reaction vessel in multiple parallel streams.

In this case, transfer means may be provided for transferring plant material from the exit of the reactor vessel to a further conveying means, the transfer means being configured to transfer multiple portions of plant material exiting the reaction vessel at a given time, to the further conveying means, such that the multiple portions of plant material are arranged in sequence along the direction of travel of the further conveying means. In an embodiment the apparatus further comprises a portion of the conveying means arranged so as to cause vibration. The vibrating conveyor can be used to load the machine which will singulate the leaves onto the conveyor belt.

In the case that the herb is basil or for baby leaves such as rocket it has been found that the most favourable results are obtained at an exposure temperature of 18°C to 30°C, preferably 25°C, an exposure or dwell time of 2 minutes and a fog microdroplet size of 5 microns, moving towards the leaves at a flow of 5-10m/s so that the fog impinges on the leaves. The best results have been found to be when using electrolysed water at 1 150mV (with a concentration of 80ppm chlorine, more specifically as hypochlorous acid) which is then passed over the evaporator or vaporiser.

In a second aspect the invention may provide an apparatus for treating plant material, comprising a reactor vessel, the reactor vessel comprising:

• at least one inlet for allowing ingress of sanitised water;

· means for creating electrically activated water at 1150mV and 30-80ppm Chlorine

• means for causing vaporisation of the water into a fog atmosphere;

• conveying means for conveying the plant material from an entrance to an exit of the reactor vessel; • flow control means for urging the fog atmosphere towards the conveying means;

• flow direction means for applying a direction to the flow of fog atmosphere so as to impinge fog droplets onto the cut plant material; and

• further conveying means for conveying the plant material away from the exit of the reactor vessel.

In an embodiment of the apparatus the flow direction means comprise a venturi or flow restriction device arranged to funnel fog droplets onto the cut plant material. Preferably the flow restriction device has an entrance having a first diameter, a portion arranged to funnel fog droplets to the cut plant material at the exit of the flow restriction device. The funnel portion preferably reducing the diameter at the entrance, typically around 10cm, by at least 1/3 across a few centimeters. This arrangement is analogous with the way a simple carburettor works. The transfer means of an embodiment are adapted to transfer a plurality of portions of plant material exiting the reactor vessel at a given time to the further conveying means such that the plurality of portions are placed on the further conveying means so as to provide a sequence of portions arranged in the direction of travel of the further conveying means. The invention will now be described by way of example with reference to the following Figures in which:

Figure 1 is a perspective view from one end of an apparatus with fog atmosphere delivery system for carrying out an example of a method according to the first aspect of the invention;

Figure 2 is a side view of an apparatus for carrying out an example of a method according to the first aspect of the invention; Figure 3 is a chart showing a reduction in the microbes on leaves after carrying out the method according to the first aspect of the invention; Figures 4a and 4b are graphs illustrating the weight gain of spinach and rocket after carrying out the method according to the invention; and

Figure 5 is a photo image in greyscale showing a sample of rocket, untreated in the left hand image and after processing with a method according to the first aspect of the invention in the right hand image.

Referring to Figures 1 and 2, an apparatus 10 for treating cut herbs or salads comprises a weighing station (not shown) in which balances are located for weighing a portion of cut herbs. In the case of babyleaf salads there is a conveying means into the reaction vessel 12 and out of the reaction vessel, leading to multihead weighing and bagging operation (not shown). A conveyor belt 14 has a first section 14a leading from a product entrance point 18 of the insulated reactor vessel 12. Second, third and fourth sections 14b, 14c, 14d of the conveyor belt are located within the reactor vessel 12, the second section 14b being located adjacent the outlet of a fog delivery system 20 and subject to a directed, restricted inflow of humid fog atmosphere. Other sections 14c, 14d are similarly located adjacent fog delivery systems. The sections 14a, 14b, 14c and 14d being horizontal.

A humidity generator 26 provides water vapour for the reactor vessel. The fog cloud generated in this way is directed via the piping 60 towards entrances for the sections 14b. 14c and 14d of the conveyor belt. The shaping and diameter of the exit point 62 of the piping 60 has been designed and optimised to give the speed and composition of the fog entering the conveyor of the reaction vessel the correct properties such that it is absorbed into the surface of the leaf material. An exhaust outlet 28 allows vapour to be discharged from the reactor vessel, while a removable hood 30 and panels on the reaction vessel 12 allows access to the conveyor belt 14, e.g. for cleaning.

In use, cut herbs and baby leaf salads are held in a cold store, at a temperature of around 5°C, before being transferred to the weighing station. The cold store may or may not be humidified. At the weighing station, the herbs are divided into portions of around 20-1 OOg and placed onto the conveyor belt 14, which transports the herb portions into and through the reactor vessel 12. The herb portions are placed on the conveyor belt in pairs, such that each one of the pair travels on a respective part 14-1 , 14-2 of the conveyor belt.

In an embodiment (not shown) a portion of the conveying means is arranged so as to cause vibration. The vibrating conveyor can be used to load the machine which will singulate the leaves as they enter or exit the reactor vessel onto the conveyor belt. The conveyor belt 14 carries the herbs along the conveyor, into the fog atmosphere and the directed streams of fog. Water vapour condenses on the cold herbs, thus increasing the water content of the herbs. Additionally, in certain applications, the latent heat released by the condensing steam causes a "heat shock" effect, which causes oils to be released from the herbs and to become concentrated at the herb surface.

The speed of the conveyor belt 14 is 2 m/min and is chosen such that the herbs remain inside the humidity cloud for about 2 minutes (the conveyor length and speed may be regulated to vary the exposure time of the herbs to the humidity cloud). After this time, the herbs travel on section 14d of the conveyor belt and leave the reactor 12 via the product exit point 24. Each of the portions are deposited onto a further conveyor belt such that they form a single column extending in the direction of travel of the further conveyor belt. The further conveyor belt transfers the herb portions to a wrapping and weighing station (not shown) at a rate of 40 portions per minute. At the wrapping and weighing station, the herbs are weighed and flow-wrapped, that is, they are wrapped in film, to provide a package having a longitudinal seal and two crimped end seals, as is known in the art. The time between the herbs leaving product exit point of the reactor vessel and the flow-wrap process can be completed is less than one minute. The packaged herbs are returned to a cold store within one hour of exiting the reactor vessel. The method and apparatus of the invention provide an improvement in freshness and sanitisation that are long lasting. This means it is also possible to batch treat the leaves rather than treating them as part of an in-line process as described above.

Examples

The following worked examples are given by way of illustration only.

The use and effect of electrolysed water is illustrated in Figure 3. The electrolysed water is demonstrated to reduce microbes. Most effects are reported as a 10 or 20 fold decrease in microbes (1-2 log reductions in microbes). The example in Figure 3 shows this result for leaves well within 10 minutes and most commonly within 2 minutes. The weight gains and effects on microbes are demonstrable with electrolysed water and not pure water.

Example 1 - Rocket Leaf

Examples 1 to 10 on the chart in Figure 4a show the comparative results of rocket leaves processed under the same conditions; exposed at a temperature of around 25°C, a dwell time (or exposure to fog droplets) of 2 minutes. The microdroplet size was 5 microns. The fog and the conveyor effect was such that the fog was caused to move towards the leaves at a flow of 5-10m/s so that the fog impinges on the leaves. These results have been using electrolysed water at 1150mV (with a concentration of 80ppm chlorine, more specifically as hypochlorous acid). The weight before the process and the weight after the process was recorded. Thus the change in weight arising from the treatment was measured.

The chart shows an indication that with a 2 minute dwell time leaves show an increase in weight 4-5%, this figure is controlled by the volume of fog introduced and a greater increase in weight is predicted to be achieved with a greater volume of fog.

A before and after photograph was taken. The results are given in the Figure 5 photo image. The before treatment photo is shown in the left hand image and in the right hand image is a photo showing rocket leaves after processing with a method according to the invention as described above. Example 2 - Spinach Leaf

Examples 1 to 7 on the chart in Figure 4b show the comparative results of spinach leaves processed under the same conditions; exposed at a temperature of around 25°C, a dwell time (or exposure to fog droplets) of 2 minutes. The microdroplet size was 5 microns. The fog and the conveyor effect was such that the fog was caused to move towards the leaves at a flow of 5-10m/s so that the fog impinges on the leaves. These results have been using electrolysed water at 1150mV (with a concentration of 80ppm chlorine, more specifically as hypochlorous acid). The weight before the process and the weight after the process was recorded. Thus the change in weight arising from the treatment was measured. The chart shows an indication that with a 2 minute dwell time the leaves show an increase in weight 2-3%, this figure is controlled by the volume of fog introduced and a greater increase in weight is predicted to be achieved with a greater volume of fog. Various modifications may be made to the described embodiment without departing from the scope of the present invention. The structure and orientation of the apparatus body and air or fog inlets may be of an alternative design and shaping. The conveying means could be of a different design or construction. The conveyor could be cut half way, with a drop, causing the leaves to tumble and turn over. The apparatus may comprise any suitable material and the conveying means may be of any length and thickness. Alternative forms of construction may be considered. In addition examples are given for cut plant material but the process and apparatus could be used with some fruit and salad items such as berries, cucumbers, peppers and tomatoes.