Method and apparatus for the application of volatile substances conveyed in carrier gas

Abstract: The invention relates to a method and apparatus for treating a material particularly foodstuffs, pharmaceutical compositions etc. The method comprises placing a material to be treated in a vessel capable of evacuation, evacuating the vessel and contacting the material with a volatile substance entrained in a carrier gas. Preferably the volatile substance is a natural food acid such as acetic or carbonic and the carrier gas is nitrogen or carbon dioxide.

Description: This invention relates to a method for the treatment of a solid material to human consumption, particularly but not exclusively a food product, with a volatile substance by use of a carrier gas or gases. Hitherto, conventional gaseous processes aimed at extending the shelf life of substances have relied on modified atmosphere packaging (MAP) procedures. In such procedures, the oxygen gas atmosphere surrounding the substance is replaced with a food grade carbon dioxide and/or nitrogen atmosphere, and high barrier colaminate packaging is used to maintain the exclusion of oxygen from the package. The slight acidity produced by the carbonic acid which results from the exposure of the substance to carbon dioxide produces a fungicidal effect. FR 2520592 A (Luissier SA) discloses a method of treating food products prior to their packing or preservation in which the food products are immersed in an atmosphere comprising, and preferably consisting wholly of, carbon dioxide. FR 2520592 A also teaches that food products maybe preserved in an atmosphere comprising a mixture of carbon dioxide and nitrogen. MAP processes have disadvantages. Whilst it has been found that an extension of the shelf life is achieved in respect of substances treated by the procedures, this extension is limited and considerable costs are involved including the cost of the specialised colaminate film packaging used. It is an object of the present invention to provide a method and apparatus to effectively treat a solid material for human consumption with volatile substances by use of a carrier gas or gases to physically or chemically alter the material, preferably rendering the material safe from fungal or bacterial spoilage or other hazards and thereby extending the shelf-life of the material. According to the present invention therefore, there is provided a method for reducing the viable microbial content of a solid material for human consumption which is susceptible to microbial spoilage, said method comprising: (a) placing the material in a vessel capable of evacuation; (b) evacuating the vessel; (c) contacting the exposed surfaces of the material with a gas mixture comprising a major portion of a carrier gas and a minor portion of a volatile substance selected from the group consisting of natural food acids, chemical biocides and mixtures thereof for a contacting period which is required to sufficiently reduce said viable microbial content to a desired value, during which period the volatile substance partitions into solution upon said exposed surfaces, wherein at the time of contacting the exposed surfaces of the material with said gas mixture, the exposed surfaces of the material have a water activity (Aw) of greater than or equal to 0.85. The process of the present invention is suitable for microbial decontamination and/or control of a wide range of food and other products including baked goods such as bread, whole grain cereals, whole or diced berries, fruits or vegetables, prepared salads, nuts in their shell, nut meats in storage awaiting drying or while undergoing further processing, vacuum packed smallgoods, cured meats, chicken flesh, carcass on abattoir chains and herbs and spices. It has been found that significant extensions in shelf life of baked goods and smallgoods (up to and exceeding 30 days) have been achieved by the inventive process. The inventive process is also suitable for microbial decontamination and/or control of pharmaceutical compositions, including individual pharmaceutical ingredients. Still further, while the inventive process may be used in isolation, it is also suitable for use with other treatment processes including for optimising dosing with antioxidants where high surface concentrations are desired, for the delivery of soluble food grade or other preservatives, for the depositing of substances onto surfaces with the possible assistance of electrostatic charges or in conjunction with conventional MAP to increase the shelf life of certain products. The means for evacuating the vessel is preferably provided by an external vacuum source. The material to be treated is preferably first evacuated rapidly to sub-ambient pressure. The material contained in the evacuated vessel is preferably contacted with the carrier gas/volatile substance by means of one or more spargers. Preferably the carrier gas is carbon dioxide and/or nitrogen gas which can be sourced from a cylinder containing the relevant compressed gas(es). For substantially extending the shelf life of foods particularly baked goods, the volatile substance is preferably a natural food acid, most preferably acetic acid and/or carbonic acid, although any other natural food acid having fungicidal or preserving qualities can be used. Alternatively, a potentially residual free chemical biocide such as hydrogen peroxide can be used. Mixtures of such volatile substances may also be used with the inventive method. The volatile substance is preferably entrained in the carrier gas by passing the carrier gas through a vessel containing the volatile substance. The carrier gas which is stripped of the volatile substance after contact with the material to be treated may be recycled through the process. Alternatively, the volatile substance can be prepackaged with the carrier gas. The carrier gas is preferably saturated with the volatile substance. Alternatively at lower concentrations the process is less biocidal and more inhibitory. The process of the invention can be performed either as a batch method or in a continuous flow mode. When a batch method is used, wrapped unsealed material is preferably loaded and unloaded into the vessel manually. When a continuous flow mode is desired, commercially available flow wrapping equipment utilising a conveyor and/or exposure in a suitable treatment tunnel can be used. For reducing microbial content of a material, the duration of exposure is that required to sufficiently reduce the total viable microbial content to a desired value and is dependant on a number of variables including surface area of the material to be treated; degree of vacuum; over-pressure; flow rates of the carrier gas; surface water activity (A w ); type and concentration of volatile material and bacterial and fungal bioburden of the material. The efficiency of the treatment method is also dependant on the interaction between the matrix geography and/or chemistry and the added volatile substance. Some materials will need to be treated individually if their matrix or final package configuration is such that, if treated simultaneously, they present a physical barrier to the volatile substance contacting the surface interface of the materials to be treated. Several cycles of vacuum and exposure may be required depending on the goods being treated and the concentration of volatile substance entrained in the carrier gas. In the case of foods, the limit to which the material to be treated can be exposed to the carrier gas/volatile substance is generally determined by the flavour resultant from the acidulation of the product. As will be explained in more detail later, certain volatile substances eg acetic acid, have an unfavourable effect on flavour due to acidulation. Other volatile substances eg carbonic acid, cause little organoleptically detectable acidulation and can in some cases actually impart a smoked flavour and/or aroma to some smallgoods. Further, some low acid foods particularly smallgoods will achieve additional colour stability after treatment. Manufacturers of bland smallgoods e.g. lower priced sandwich-type hams, etc. can overcome mild acidulation by making slight changes to their flavour formulations. In some cases, however, the additional acidulation actually aids in completion and enhancement of the flavour profile whilst achieving near to, or complete microbial stability. The applicants have noted that the acidic flavour effects resulting from the present inventive method may recede during storage. In all materials tested to date, flavour effects have in fact receded dramatically during the initial 24 hours following exposure, then more gradually on further storage. Some materials end application involves heating or cooking which will further decrease any lingering unfavourable flavour effects of the process, particularly in bland baked goods such as crumpets. Packaging materials with poor gas barrier properties or small perforations may also assist in the diffusion of volatile substances from the surface of the material/s treated by the inventive process thus reducing any acidic flavours. Conversely packaging with excellent gas barrier properties will maintain an atmosphere of volatile substances thus enhancing the preservative effect. Accordingly the barrier properties of the packaging may be chosen to suit the treated material. The material to be treated e.g. foodstuffs, should have a minimum surface water activity (A w ) of approximately 0.85 to allow the volatile substance to quickly transfer across from the carrier gas. An A w of approximately 0.95 will allow near optimum transference rates and therefore minimum exposure times. To optimise transfer rates it may be appropriate to dose all the gaseous mixture required to an over-pressure of 0.01-0.2 bar (7.5-150mm Hg) and up to 3 bar (2250mm Hg) over atmospheric pressure and allow the appropriate contact time. Lower A w foodstuffs without the addition of a small quantity of water (generally 1-2%), onto the surface of the material to be treated may require longer exposure times. This additional water can be applied as a fine mist in the case of relatively impervious products such as peppercorns or by steaming in more difficult applications. If surface wetting is a technical requirement then mild surface drying will promote the volatilisation of surface acids thereby reducing acidulation. Alternatively post-treatment surface addition of approximately 0.2% w/w of sodium bicarbonate will, in most cases, neutralise all surface acidulation. Once the desired exposure is attained, the vacuum in the vessel may be released and the treated products proceed to final packaging stages. Some post contamination protection is also offered by this invention thus mechanical and/or human double handling is feasible when using this invention. It is preferable, however, that once the surface acidulation has been decreased to minimise unfavourable acidic flavours, sometimes a requirement with bland materials, the material is handled and packed in such a manner as to minimise it from any further microbial contamination especially if a favourable environment exists to initiate and support further microbial growth. The invention will now be described by way of example only with reference to the following, nonlimiting examples and accompanying drawings in which: Figure 1 shows a schematic elevational representation of a batch treatment apparatus according to a first embodiment of the present invention; Figure 2 shows a schematic elevational representation of a continuous treatment apparatus according to a second embodiment of the present invention; and Figure 3 shows a flowchart of the treatment method and apparatus according to a third embodiment of the present invention. As shown in Figure 1, material 2 to be treated is provided in a sanitary pressure vessel 1. The vessel 1 comprises a hinged swing away lid 3 which contains a flange and seal 4. The vessel 1 is also provided with a safety vent 8, a pressure/vacuum gauge 9, a pressure regulator valve 10 and gas sparging ports 11. An external vacuum source 5 is connected by means of a line 6 and valve 7 to the vessel 1. Connected to the gas sparging ports by means of lines 12, 13, 14, 15 and valves 16, 17 and 18 is a compressed gas source 19, one or more volatile substance sources 20, preferably sparging vessels, and an aerosol trap 21. The aerosol trap 21 is intended to minimise large droplets of the volatile(s) for sealing the vessel 1. These large aerosol droplets cause undesirable spotting of the material to be treated and non-uniform distribution of the volatile(s) or the material surface. Multiple volatile substance sources 20 ensure complete saturation of the carrier gas. In the case of treatment with carbonic acid, the volatile source 20 may be at least initially filled with purified water such that bubbling of the CO 2 gas therethrough produces carbonic acid thus causing the CO 2 carrier gas to be at least partially saturated with the produced carbonic acid. Some materials will benefit more after the carrier gas, preferably food grade carbon dioxide, has been passed through multiple volatile sources solvents to achieve a mixture of volatiles in the carrier gas. Various types, combinations and concentrations of saturated carrier gases can be used to treat the material to optimise shelf life and flavour parameters, particularly various mixtures of acetic and carbonic acids and hydrogen peroxide. A carrier gas/multiple volatile mixture may be provided by mixing a group of parallel gas/volatile mixture streams after passing through their respective volatile substance sources or, a single carrier gas stream may be passed through a series of volatile sources. In use a batch of material 2 to be treated is introduced through the lid 3 into the vessel 1 and the lid is then sealed. Valve 7 is opened and evacuation is commenced by means of the vacuum pump 5. When the desired vacuum is achieved valves 16, 17 and 18 are opened and the carrier gas is forwarded from the compressed gas source 19 to the volatile substance source 20, the volatile substance thereby becoming entrained in the carrier gas, which is then introduced into the vessel 1 through sparging ports 11 to thereby contact the material 2. Valves 22 and 23 may be operated to bypass the additional volatile substance source 20 if only one volatile substance source is required. During the process the carrier gas which is at least partially stripped of the volatile substance is allowed to escape through the pressure regulator valve 10 achieving a desired process overpressure for the predetermined time of exposure. This stripped carrier gas may be recycled back to the process as mentioned above for further entrainment of the volatile substance. The duration of exposure is optimised to provide the maximum reduction in microbial bioburden while achieving the desired flavour and other properties of the material 2 being treated. Once the desired exposure is attained, the flow of carrier gas is ceased and the pressure regulating valve 10 released. The treated material 2 is then removed from the vessel and sealed. Acetic acid is a natural organic food acid with a high degree of biocidal activity and is highly soluble in carbon dioxide. The pH profile of acetic acid is shown in Table 1. pH PROFILE ACETIC ACID % ACETIC - AQUEOUS SOLUTION pH 90 -0.01 60 1.17 45 1.52 15 1.73 11 1.83 Surprisingly, the applicants have also found that carbonic acid is also suitable for the present inventive process. Carbonic acid is also a natural organic food acid, which the applicants have found, has a high degree of biocidal activity. It is also soluble in gaseous carbon dioxide and has a high degree of buffering capacity. Unexpectedly the applicants have determined that carbonic and acetic acids transferred by the inventive gaseous process yield similar titrateable acidities after the gas mixes are "stripped" of their acids by passing them through distilled and neutralised water as shown in Table 2 below. As a quality assurance method and to determine the titrateable acidity of acetic acid in a carrier gas as compared to carbonic acid in a carrier gas, the respective gaseous mixtures were passed through a neutralised and distilled water bath and titrated with 0.1 N KOH solution until the bromothymol blue indicator yielded the first faint blue colour which persisted for at least five seconds. It can be seen from Table 2 that the titrateable acidity of acetic acid and carbonic acid is virtually identical. Furthermore, an investigation by CSIRO Australia (Report FSQ96-128) concluded that the titrateable acidities were identical. ACID IN CO 2 CARRIER MIXTURE VOL. DIS. H 2 O REACTION TIME (SECONDS) FLOW RATE CO 2 TITRE 0.1 N KOH Acetic 200 10 10 l/minute 44 mils Acetic 200 10 10 l/minute 38 mils Acetic 200 10 10 l/minute 41 mils Carbonic 200 10 10 l/minute 43 mils Carbonic 200 10 10 l/minute 38 mils As shown in Figure 2, an alternative application to the batch process is to conduct the method of the invention continuously whilst conveying material through a commercially available flow wrapper 24, or similar packaging system, equipped with a conveyor 25, a gas sparging head 26 and a gas control system 27. Typically, the process can be balanced to attain treatment times of only seconds. Of course longer treatment times may be necessary depending upon a number of variables including initial microbial content. This short processing time can yield up to and exceeding 30 days extension in the acceptable shelf life of bread and other baked products. Shelf life is evaluated on the basis of flavour and aroma profiles, as well as apparent fungal and/or bacterial spoilage. An alternative embodiment of an apparatus for carrying out the inventive process is shown in Figure 3 in which compressed gas, typically carbon dioxide 51 passes through regulator 52 when valve 53 is opened. The carrier gas is transferred through transfer line TL1, to flow meter 54. Process controller 55 monitors and controls the flow of carrier gas through the flow meter 54 to the specified rate. The carrier gas is then transferred through line TL2 to the sparger 56, and sparged through the volatile substance contained in vessel 57. As mentioned above the inventive process can include one or more such vessels to provide a mixture of volatile substances in the carrier gas. If carbonic acid treatment is required vessel 57 may be at least initially filled with water. Preferably the carrier gas is saturated with volatile substance(s). The carrier gas/volatile substance mixture is then transferred through line TL3 into the liquid trap 58, to ensure that an aerosol is not transferred into line TL4. In operative mode, the gas mixture is then normally transferred through line TL4 and through valve 59, with valves 64 and 68 closed, through heating manifold 70, which is normally not in heating mode, through to product treatment container 60, which may be the final packaging; vacuum/pressure vessel; treatment tunnel or other such device as indicated in Figures 1 and 2. After the prescribed treatment the carrier gas stripped of volatile(s) may be transferred through line TL5 with valve 61 open and valve 62 closed, to compressor 63, and recycled back to compressed gas cylinder 51. Alternatively after leaving treatment container 60 the volatile(s) stripped carrier gas can be transferred through line TL5 and vented to atmosphere with valve 61 closed and valve 62 open. When a material is not being treated but it is desirable to maintain the carrier gas/volatile substance flow, especially in the case of treatment with carbonic acid, valve 59 is closed and valve 64 is opened with valve 65 closed, the carrier gas/volatile substance mixture is transferred through line TL6 to water scrubber 66 where the volatile substance is stripped from the carrier gas and the gas is vented to atmosphere or recycled. Quality measurements of the carrier gas and the volatile substance are performed by closing valve 59 and 64 and opening valve 65, transferring the gas mixture through line TL7 to quality control station 67 for testing. Test data from control station 67 is sent to process controller 55 which monitors and controls the flow of carrier gas through the flow meter 54. If station 67 identifies that the carrier gas is being slowly diluted by atmospheric gas the process controller 55 may increase the flow rate through flow meter 54, until the predetermined maximum volatile substance transfer rate is achieved, at which point a predetermined percentage of recycled carrier gas is vented to atmosphere and an equivalent volume of new carrier gas is fed into the circuit from compressed carrier gas vessel 51. If a high concentration of a volatile substance or a mixture of volatile substances is required for a given application, the standard carrier gas/volatile substance mixture transferring through line TL4 may be dosed with additional volatiles by injection of a fine aerosol of the desired volatile substance from a storage tank/atomiser 69 through opened valve 68. The gas mixture/aerosol continues to transfer along line TL4 and is heated to beyond the vaporisation point of the added aerosol in the heated manifold 20, from where it enters the treatment container 60 as normal. Prolonged production runs employing this additional dosage system may cause condensation on the inner walls of treatment vessels/tunnels if they are not heat lagged. The following examples illustrate and substantiate various aspects of the present invention. EXAMPLE 1A - SANDWICH HAM In this example, a sandwich ham was treated in accordance with the present inventive method. The ham was placed in the vessel, the vessel evacuated and then supplied with a CO 2 /acetic acid gas mixture or CO 2 /carbonic acid gas mixture for the designated period. The gas flow was constant such that the vessel maintained an overpressure 0.01-2 bar above atmospheric pressure. The sandwich ham was in plastic bags and a degree of pressure was allowed to develop in the plastic bags during treatment. After the designated period the gas flow was stopped, the bag containing the ham closed and shaken slightly for 15 seconds to provide better contact with the carrier gas/volatile substance mixture. The vessel was then vacuum flushed again and an additional exposure to the gas mixture performed along with the 15 second post-treatment contact. The majority of the gas mixture entering the vessel escaped with approximately 50% of the residual gas mixture being expelled manually prior to sealing of the plastic bags. The samples were then stored for approximately one hour prior to microbiological analysis. The results provided under Table 3 follow on page 15. As can be seen from Table 3, there has been a substantial reduction in the bioburden following application of the inventive process. For treatment with a carrier gas/acetic acid, the initial total plate count of 3.4 x 10 4 , and total spores of 35 was reduced to total plate count 65-70, total spore count 10-40. Using a carrier gas/carbonic acid mixture an initial total plate count of 2 x 10 6 and total spores of 250 was reduced to total plate count of 7 x 10 3 and total spores 500 at gas flow rate of 10 litres/minute. At a higher gas flow rate of 20 litres/minute total plate count was reduced to less than 10 and total spores to 45. EXAMPLE 1B - SANDWICH HAM In this example sandwich ham is treated with a volatile substance comprising 50% carbonic acid and 50% hydrogen peroxide. As with Example 1A, the ham was placed in the vessel and the vessel evacuated and exposed to the carrier gas/volatile substance mixture. The ham was then subjected to the 15 second post-treatment contact time with agitation. The vessel was then vacuum flushed again and additional exposure to the gas mixture performed followed by the same 15 second post-treatment contact. Shelf life observations were made approximately four days after treatment and further observations were made from nine to twenty days after treatment. The results are provided under Table 4. It can be seen from the microbiological results provided under Table 4 that this particular gas mix is very effective in reducing the microbiological counts. Total treatment times of 10, 20 and 60 seconds resulted in proportional reductions down to 2 vegetative and less than 1 spore organism per gram of sample. It has been observed that hydrogen peroxide increases the pink coloration and extends the shelf life of the pink coloration of some smallgoods. This effect appears to be intermediatory in efficiency between carbonic and acetic acids. Again, smoked aromas were observed along with slight background volatility in some instances. EXAMPLE 2A - CRUMPETS In this example the same process as Example 1A, was applied to crumpet fingers. Namely the finger(s) were placed in the vessel, the vessel evacuated and then exposed to the carrier gas/volatile substance mixture followed by a 15 second post treatment contact with agitation. The vessel was then vacuum flushed again and an additional exposure to the gas mixture performed followed by the same 15 second post-contact treatment. The results are provided under Table 5. As can be seen from Table 5 a significant seven day shelf life extension of crumpets was achieved with CO 2 /carbonic acid gas mixture treatment. Not all mould spores were killed or completely inhibited, however, colony growth was random indicating entire surface area had been uniformly treated. No unfavourable acidic flavours were detected. The six second exposure time was found to be optimal. Greater exposures appeared to make no improvement. Indeed it is not entirely clear why higher exposure times did not result in additional benefit. This appears to be a peculiarity of treatment with carbonic acid. For treatment with CO 2 /acetic acid 90%/carbonic acid 10% mixture an indefinite shelf life extension was achieved however, after assessing the resultant surface acidulation the realistic shelf life extension was reduced to 13 days. The manufacturers of these types of products must consider other quality parameters such as syneresis and related textural problems which may further reduce the shelf life extension, however the inventive process will still achieve an increase in food safety to the consumer. EXAMPLE 2B - CRUMPETS In the example the same process as Example 1B was applied to crumpet finger(s). The results are shown in Table 6. It can be seen from the microbiological results provided under Table 6 that this particular gas mix is very effective in reducing the microbiological counts. Total treatment times of 10, 20 and 60 seconds resulted in proportional reductions down to six vegetative and less than 1 spore organism per gram of sample. Example 3 - Peppercorns The same process as Example 1B was applied to peppercorns at 0.75 A w without the addition of any surface water. The results are shown in Table 7. It can be seen from the microbiological results provided under Table 7 that this particular gas mix has been the most effective in reducing the microbiological counts in black peppercorns. Total treatment times of 10; 20 and 60 seconds resulted in close to proportional reductions down to 9.0 x 10 7 vegetative and 7.5 x 10 3 spore organisms per gram of sample. Although the nature of hydrogen peroxide did not require a high water activity for "transference" to the peppercorn, it is not entirely clear whether all of the carbonic acid in the carrier gas would have been deposited on the peppercorn surface. The applicant believes that the actual proportions of the individual volatile substances, in the volatile substance sources, or entrained in the carrier gas may differ from the proportions that actually make contact with the material being treated. The mechanism of transfer is not yet entirely understood. Not wishing to be bound by any particular theory the applicant assumes that there are at least significant quantities of each individual volatile substance present in the carrier gas which transfer to the material being treated. However it is thought that the hydrogen peroxide at least would react more evenly if the peppercorns were at a higher water activity. The volatile/oxidant flavour which was just perceptible at the 60 second exposure time would not normally be noticeable in this materials end application. From the data collected to date it is clear that exposure time and volatile concentration typically increase the efficiency of this inventive process. It is also expected that an increase in pressure and temperature may assist the efficiency of the inventive process. Some heat treatment experiments which were performed by the applicants at maximum acetic acid concentrations of 0.08%, which is negligible, indicate that the spore organisms are highly stressed. It is also expected that the inventive process may utilise surface heat of the material to volatilise any excessive acidic volatiles i.e. reduce acidulation. The applicants have also found that even with low acetic acid concentrations, if the treatment vessel is maintained at an over-pressure of up to 3 bar over atmospheric pressure, up to five days shelf life extension may be obtained on crumpets. It can be seen that the present inventive method is not only suitable as a biocidal process but in lower concentrations has an inhibitory function and substantially extends the shelf life of certain products. It is also envisaged that the inclusion of a low concentration of acetic acid in the carrier gas/volatile substance mixture may increase the post-protection potential of the gas mixture. Typically such a gas mixture may be made from the following volatile substances e.g. carbonic acid 50%, hydrogen peroxide 30-40%, acetic acid 10-20%. It has been found that some food products, treated by the method of the invention, particularly bland food products can develop a slightly acidic taste. This can be masked by the use of spreads or condiments or flavour disguising agents. By means of the invention it is possible to treat a material with a volatile substance to alter its physical or chemical characteristics whilst not severely adversely affecting the properties of the treated material. The process of the invention does not require specialised packaging or costly changes to existing equipment.

Claims: A method for reducing the viable microbial content of a solid material for human consumption which is susceptible to microbial spoilage, said method comprising: (a) placing the material in a vessel capable of evacuation; (b) evacuating the vessel; (c) contacting the exposed surfaces of the material with a gas mixture comprising a major portion of a carrier gas and a minor portion of a volatile substance selected from the group consisting of natural food acids, chemical biocides and mixtures thereof for a contacting period which is required to sufficiently reduce said viable microbial content to a desired value, during which period the volatile substance partitions into solution upon said exposed surfaces, wherein at the time of contacting the exposed surfaces of the material with said gas mixture, the exposed surfaces of the material have a water activity (Aw) of greater than or equal to 0.85. A method according to claim 1. wherein (b) and (c) are repeated sequentially. A method according to claims 1 or 2, wherein (c) comprises feeding the gas mixture to the vessel to achieve a desired over-pressure in the vessel during the contacting period. A method according to claims 1 or 2, wherein (c) comprises continually feeding the gas mixture to the vessel to maintain a desired over-pressure in the vessel during the contacting period. A method according to claims 3 or 4, wherein the over-pressure is up to 3 bar (2250mm Hg) above atmospheric pressure. A method according to claim 2, wherein prior to repeating (b) and (c), said material is agitated. A method according to claims 1 or 2, wherein (c) comprises contacting the exposed surfaces of the material with a gas mixture comprising a major portion of a carrier gas and a minor portion of a volatile substance selected from the group consisting of natural food acids, chemical biocides and mixtures thereof for a contacting period of 20 seconds or less. A method according to claims 1 or 2, wherein (c) comprises contacting the exposed surfaces of the material with a gas mixture comprising a major portion of a carrier gas and a minor portion of a volatile substance selected from the group consisting of natural food acids, chemical biocides and mixture thereof for a contacting period of 10 seconds or less. A method according to any one of the preceding claims, wherein the material to be treated is chosen from the group consisting of foods, pharmaceutical compositions, and ingredients of pharmaceutical compositions. A method according to any one of the preceding claims, wherein the volatile substance is a natural food acid. A method according to claim 10, wherein the natural food acid is acetic acid. A method according to claim 10, wherein the natural food acid is carbonic acid. A method according to any one of claims 1 to 9, wherein the volatile substance is a chemical biocide. A method according to claim 13, wherein the chemical biocide is hydrogen peroxide. A method according to any one of claims 1 to 9, wherein the volatile substance present in the gas mixture is a mixture of acetic acid and carbonic acid. A method according to claim 15, wherein the volatile substance present in the gas mixture consists of 90% (w/w) acetic acid and 10% (w/w) carbonic acid. A method according to any one of claims 1 to 9, wherein the volatile substance present in the gas mixture is a mixture of carbonic acid and hydrogen peroxide. A method according to claim 17, wherein the volatile substance present in the gas mixture consists of 50% (w/w) carbonic acid and 50% (w/w) hydrogen peroxide. A method according to any one of claims 1 to 9, wherein the volatile substance present in the gas mixture is a mixture of acetic acid, carbonic acid and hydrogen peroxide. A method according to claim 19, wherein the volatile substance present in the gas mixture consists of 10-20% (w/w) acetic acid, 50% (w/w) carbonic acid and 30-40% (w/w) hydrogen peroxide. A method according to any one of the preceding claims, wherein the carrier gas is saturated with the volatile substance. A method according to any one of the preceding claims, wherein the volatile substance is entrained in the carrier gas by passing the carrier gas through a vessel(s) containing the volatile substance(s) in liquid form. A method according to any one of claims 1 to 21, wherein the volatile substance is prepackaged with the carrier gas. A method according to any one of claims 1 to 21, wherein the volatile substance is injected directly into a gas line feeding the carrier gas to the vessel thereby forming said gas mixture. A method according to claim 24, wherein after said volatile substance is injected, said gas line is heated to maintain said gas mixture in the gaseous state prior to entry into said vessel. A method according to any one of the preceding claims, wherein the vessel is initially evacuated rapidly to sub-ambient pressure. A method according to any one of the preceding claims, wherein the carrier gas is carbon dioxide and/or nitrogen gas. A method according to any one of the preceding claims, wherein the method is conducted either batchwise or continuously. A method according to any one of the preceding claims, wherein at the time of contacting exposed surfaces of the material with said gas mixture, the water activity (Aw) of exposed surfaces of the material is greater than or equal to 0.95. A method according to any one of the preceding claims, further comprising: (d) packing the material within gas barrier packaging to form and/or maintain an atmosphere of said volatile substance substantially in equilibrium with the volatile substance that has partitioned into solution upon said exposed surfaces of the solid material.

Inventors: INGLIS ANDREW STERLING, LARK DAVID JAMES, INGLIS, ANDREW STERLING, LARK, DAVID JAMES
Applicants: VAPOREX PTY LTD
Application year: 1996
Main classification: A61L2
IPC codes: A61L2, A23L3