AU734421B2 - Method and apparatus for applying volatile substances to materials - Google Patents

Description

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT 0*

ORIGINAL

DAVID JAMES LARK and ANDREW STIRLING INLIO Name of Applicant: Actual Inventors: Address of Service: David James LARK and Andrew Stirling INGLIS ADDRESS FOR SERVICE

ALTERED

AF.DWIN Lce F. Co 60 MAR EET Rcw a<ei o T- ,OW( 2000 VWSW_ 2e-E.

"METHOD AND APPARATUS FOR APPLYING VOLATILE SUBSTANCES TO MATERIALS" Invention Title: Details of Associated Provisional Application No. PO 8738 dated 22nd August, 1997 The following statement is a full description of this invention, including the best method of performing it known to us:- 1, i I' -2- METHOD AND APPARATUS FOR APPLYING VOLATILE SUBSTANCES TO

MATERIALS

FIELD OF THE INVENTION This invention relates to a method and apparatus for the treatment of a material with a volatile substance entrained in a carrier gas. In a particular application of the invention, the method and apparatus is used to treat a food or pharmaceutical product or ingredient with a natural food acid such as carbonic acid for the purpose of achieving at least partial microbial decontamination and/or shelf-life extension.

BACKGROUND OF THE INVENTION: So: 10 Hitherto, conventional gaseous processes aimed at extending the shelf-life of materials prone to microbial spoilage have relied on modified atmosphere (MAP) procedures. In such procedures, the oxygen gas atmosphere surrounding the material is S"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.

15 The slight acidity produced by the carbonic acid which results from the exposure of the material to carbon dioxide produces a fungicidal effect. However, MAP processes have disadvantages. That is, whilst it has been found that an extension of the shelf-life is achieved in respect of materials treated by the procedures, this extension is limited and considerable costs are involved including the cost associated with the specialised S 20 colaminate film packaging used.

In copending Australian patent application No. 75449/96 (the entire disclosure of which is to be regarded as incorporated herein by reference), a method and apparatus is described for extending the shelf-life of materials prone to microbial spoilage by treating the materials with a volatile substance such as a natural food acid. The method described in this copending application involves prior evacuation of the vessel containing the material to be treated and, while this may lead to the more effective treatment of some materials, the inventors have now found that prior evacuation of the vessel containing the material is not necessary for the satisfactory extension of shelflife.

SUMMARY OF THE INVENTION: Thus, in a first aspect, the present invention provides a method for reducing the viable microbial content of a solid material for human consumption, which is susceptible to microbial spoilage, said method comprising the steps of: entraining a volatile substance in a liquid form, selected from the group consisting of natural food acids, chemical biocides and mixtures thereof, in a stream of a carrier gas to form a gas mixture substantially free of particles of the volatile substance comprising a major portion of the carrier gas and a minor portion of the volatile substance, and contacting exposed surfaces of the material with the gas mixture for a contacting period of 2 minutes or less during which time 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, 15 the exposed surfaces of the material have a water activity (Aw) of greater than or equal to 0.85; wherein said method does not involve, prior to step and/or a *o *.step of subjecting the material to a vacuum.

Preferably, the material is a food or pharmaceutical product or 20 ingredient and the method achieves at least partial microbial decontamination and/or shelf-life extension of the food or pharmaceutical product or ingredient.

The volatile substance is preferably entrained in the carrier gas in saturating amounts. The material may be contacted with the volatile 25 substance/carrier gas mixture provided at pressures greater than ambient; The method may be performed using a suitable vessel to contain the material during contact with the volatile substance/carrier gas mixture.

In a second aspect, the present invention provides an apparatus for treating a material comprising: a vessel for containing the material; means for entraining a volatile substance in a carrier gas; and means for contacting the material contained within the vessel with the volatile substance entrained in the carrier gas.

Preferably, the vessel is adapted to allow the volatile substance/carrier gas mixture to be present at pressures greater than ambient. Open vessels may, however, also be used.

Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like are to be construed in an inclusive as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to".

Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed in Australia before the priority date of each claim of this application.

DETAILED DISCLOSURE OF THE INVENTION: Materials that can be treated by the method of the invention include 15 any substance for which it is desired to have its chemical and/or physical characteristics altered by means of volatile substances. The method of the invention is suitable for microbial decontamination and/or control of a wide range of food products and ingredients including, but not limited to, baked 2 goods such as bread, whole grain cereals, whole or diced berries, fruits or 20 vegetables, prepared salads, nuts in their shell, nut meats in storage awaiting drying or while undergoing further processing, cheese, smallgoods, cured meats, chicken flesh, carcass on abattoir chains, sea and fresh water foodstuffs, and herbs and spices. The method of the invention is also suitable :for microbial decontamination and/or control of pharmaceutical compositions S 25 and individual pharmaceutical ingredients, for head space sanitation and control of processing plant equipment. Still further, while the method of the invention may be used in isolation, it is also suitable for use with other treatment processes including for optimising dosing with anti-oxidants 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 MAP to increase the shelf-life of certain products.

The method of the present invention may be performed batch-wise or continuously, and preferably in a suitable vessel. Preferably, the vessel is adapted to allow the volatile substance/carrier gas mixture to be present at pressures greater than ambient. For batch treatments, the material may be placed in the vessel using an infeed hopper attached to the vessel through, for example, a suitable valve. Alternatively, wrapped unsealed material may be placed in the vessel manually. For continuous treatments, the material may be placed in and out of the vessel by placing the material on a conveyor and passing the conveyor through the vessel and/or via rotary locks or other similar devices.

The duration of contact between the material and the volatile substance/carrier gas mixture may vary, as necessary, to achieve the desired aim, however the duration of the contact should always be for a period of 2 minutes or less. For example, for microbial decontamination 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; flow rates of the carrier gas; surface water activity type and concentration of volatile S: 15 substance and the 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.

Typically, the duration of the contact between the material and the 20 volatile substance/carrier gas mixture will be in the order of 0.05 to 2mins;, more preferably, 0.15 to 0.5 mins.

•Contact between the material and volatile substance/carrier gas mixture 0o* may be achieved by means of one or more spargers. To assist contact between the material and volatile substance/carrier gas mixture, the Vessel 25 may be provided with means for tumbling and/or passing thematerial (eg.

through falling under gravity) through the 15 volatile substance/carrier gas mixture.

ooo The method of the present invention may comprise multiple (eg. up to 3 times) exposures contacting) of the material to a volatile substance/carrier gas mixture. The volatile substance(s) used in each exposure may be the same or different. Where multiple exposures are performed using a single vessel, the vessel may be evacuated between exposures and/or flushed with a suitable gas (eg. carrier gas).

The volatile substance can be any substance selected from the group consisting of natural food acids, chemical biocides and mixtures thereof. The volatile substance may be entrained in an inorganic or organic gas, and may chemically and/or physically alter the treated material. For example, for microbial decontamination and/or extending the shelf-life of food and pharmaceutical products and ingredients, the volatile substance is preferably a natural food acid, more preferably carbonic acid and/or acetic acid, although any other natural food acid having microbicidal or preserving qualities can be used or other volatile preservative substances. Alternatively, a potentially residue-free chemical biocide such as hydrogen peroxide can be used. Mixtures of such volatile substances may also be used. The ratios of the component volatile substances in such mixtures will typically vary depending on the physical and chemical nature of the material being o *oo o *e treated. However, for mixtures such as carbonic acid/acetic acid, carbonic acid/hydrogen peroxide and acetic acid/hydrogen peroxide, the ratio of the component volatile substances may be within the range of 1: 10 to 10:1. Moreover, for the mixtures carbonic acid/hydrogen peroxide and acetic acid/hydrogen peroxide, the ratio of the component volatile substances is preferably within the range 1:5 to 5:1, more preferably, about 1:3.

The volatile substance is preferably entrained in the carrier gas by passing the carrier gas through a vessel or vessels containing the volatile substance or by other 10 means by which a sufficient concentration of the volatile substance can be entrained in the carrier gas without the formation of an aerosol. A multiple volatile substance/carrier gas mixture may be provided by mixing a group of parallel preferred volatile substance/carrier gas mixture streams after passing through their respective "volatile substance sources or, alternatively, a single carrier gas stream may be passed through a series of volatile substance sources.

Alternatively, the volatile substance can be prepackaged with the carrier gas. The volatile substance is preferably entrained in the carrier gas in saturating amounts.

The carrier gas is preferably carbon dioxide and/or nitrogen gas which can be sourced from a cylinder containing the relevant compressed gas(es). The carrier gas, which is fully or partly stripped of the volatile substance after contact with the material S 20 to be treated, may be recycled.

The volatile substance and/or carrier gas may be heated to increase volatility and hence concentration of the volatile substance in the carrier gas. Reduction in carrier gas usage and other efficiencies may result.

In the case of food products and ingredients, the limit to which the material to be treated can be contacted with the volatile substance/carrier gas mixture is generally determined by the flavour resultant from the acidulation of the product. That is, certain volatile substances (eg. acetic acid), have an unfavourable effect on flavour due to acidulation. However, other volatile substances (eg. carbonic acid), have been found to cause relatively little organoleptically detectable acidulation and can in some cases actually impart an appealing smoked flavour and/or aroma. In any case, the inventors have noted that the acidic flavour effects resulting from the method of the invention may recede during storage. Further, some materials end use involves heating or cooking (eg. crumpets), which will also decrease any lingering acidic flavour effects of the method. Mild surface drying to promote volatilisation of surface acids and post-treatment surface addition of alkalis such as approximately 0.2% w/w of sodium bicarbonate may also be used to reduce or avoid acidic flavour effects. It is also preferred that when the material to be treated has critical flavour specifications, the concentration of the volatile substance in the carrier gas be closely monitored and controlled.

Subsequent packing in 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 method of the invention thus reducing any acidic flavour effects. Conversely, packaging with excellent gas barrier properties will aid to maintain an atmosphere of S: 15 volatile substances thus enhancing the preservative effect of the method.

S•Accordingly, the barrier properties of the packaging may be chosen to suit the "..treated material.

S""The material to be treated should have a minimum surface water activity (Aw) of approximately 0.85 to allow the volatile substance to quickly 20 transfer across from the carrier gas. An Aof 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 0.01-0.25 bar (7.5-190mm Hg) and up to. 3 :bar -(2250mm Hg) above atmospheric pressure and allow the appropriate contact 25 time. Lower Aw foodstuffs without the addition of a small quantity of water (generally 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, preferably, by steaming in more difficult applications.

While particularly suited to use with water soluble volatiles, the method of the invention may also be used with other applications such as those requiring the transfer of volatile substances that are soluble in, for example, lipids or other organic or inorganic solvents other than water (eg.

some anti-oxidants).

Some post-contamination protection is also offered by the method of the invention and thus mechanical and/or human double handling is feasible.

8 It is, however, preferable that where surface acidulation has been decreased to minimise acidic flavour effects, sometimes a requirement with bland materials, the material be handled and packaged in a manner so as to minimise microbial contamination.

The method of the invention may also be performed in combination with one or more treatments of the material in accordance with the method described in copending Australian patent application No. 75449/96.

In addition, the inventors have found that it can be advantageous to dip or spray the material in/with a solution of the volatile substance, preferably prior to contacting the material with the volatile substance/carrier gas mixture. Dipping may be readily achieved by, for example, passing a conveyor with the material through a tank of an aqueous solution of the volatile substance. Following dipping, the material may then o* oo *o o*oo -9be conveyed to a suitable vessel for treatment with a volatile substance/carrier gas mixture in accordance with the method of the invention.

The invention will hereinafter be further described by way of reference to the following, non-limiting examples and accompanying figures.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES: Figure 1 provides a schematic representation of a continuous treatment apparatus according to the invention, wherein the material is fed to a commercially available packaging machine for treatment and contacted with a volatile substance/carrier gas 1 mixture provided through a gas sparging head.

Figure 2 provides a schematic representation of an alternative continuous e• treatment apparatus according to the invention, wherein a treatment vessel is isolated by *0o.

rotary vacuum locks providing supplementary treatment stages.

S* •Figure 3 provides a schematic representation of a further alternative continuous apparatus according to the invention, wherein the material falls in counter-current flow ,o 15 to a volatile substance/carrier gas mixture.

MODE(S) FOR CARRYING OUT THE INVENTION A 00 As shown in Figure 1, continuous treatment of materials in accordance with the method of the invention may be achieved through a dedicated treatment system or commercially available packaging machine equipped with a conveyor a gas 20 sparging head and a gas control system Connected to the gas sparging head (3) by means of lines and and valves (10) and (11) is a compressed gas source one or more volatile substance sources preferably sparging vessels, and an aerosol trap The aerosol trap (14) is intended to minimise large droplets of the volatile(s) which can cause undesirable spotting and non-uniform distribution of the volatile(s) on the material surface. Multiple volatile substance sources (13) may be used to assist complete saturation of the carrier gas.

In the case of treatment with carbonic acid, the volatile substance source (13) 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 type, combinations and concentrations of saturated carrier gases may 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 multiple volatile substance/carrier gas mixture may be provided by mixing a group of parallel preferred volatile substance/carrier gas mixture streams after passing through their respective volatile substance sources or, alternatively, a single carrier gas stream may be passed •1 through a series of volatile substance sources.

l0 In use, a batch of material (15) to be treated is introduced to a commercially available packaging machine The carrier gas is forwarded from the compressed gas source (12) to the volatile substance source the volatile substance thereby *°becoming entrained in the carrier gas, which is then introduced into the packaging machine through gas sparging head to thereby contact the material Valves (16) and (17) may be operated to bypass the additional volatile substance source (13) if only one volatile substance source is required. The carrier gas, which is at least partially stripped of the volatile substances, is allowed to escape through a pressure regulator valve achieving a desired process overpressure for the desired contact time.

The duration of contact between the material and the volatile substance/carrier 20 gas mixture may be optimised to provide the maximum reduction in microbial bioburden while achieving the desired flavour and other properties of the material being treated. Once the desired duration of contact is attained, the flow of carrier gas is ceased and the pressure regulating valve released. The treated material is then removed from the vessel and packaged.

As shown in Figure 2, an alternative continuous treatment of materials in accordance with the method of the invention is achieved through a dedicated treatment system wherein material (23) is fed to a first rotary vacuum lock (24) (or other effective cavity mechanism) then, in turn, to conveyor (25) within treatment vessel (26) where the material is contacted with a volatile substance/carrier gas mixture, provided through gas sparging heads without prior evacuation of the treatment vessel (26) -11in accordance with the method of the invention. From the conveyor, the treatment material is transferred to a collecting hopper (28) via a second rotary vacuum lock (29) (or other effective cavity mechanism). The first and second rotary vacuum locks (24) and (29) isolate the vessel and permit operation of a two or three stage process wherein the material is also treated within the first and/or second rotary vacuum locks (24) and (29) with supplemental treatment(s) involving contacting the material with a volatile substance/carrier gas mixture preferably following evacuation The stage performed in the treatment vessel (26) may be of considerably longer duration 10 than either or both of the supplementary treatment(s) and may benefit from cost efficiencies associated with carrier gas recycling. Each of the stages could use the same S, or different volatile substances.

As shown in Figure 3, continuous treatment of materials in accordance with the S* •method of the invention may also be achieved through a dedicated treatment system, equipped with a means (31) such as an infeed hopper to deliver material (32) through a 15 suitable valve (33) (or conveyor) to the top of a vertical vessel (34) provided with one or more gas sparging heads (35) and material outlet valve (36) (or conveyor) located within the base. A collecting hopper (37) is provided adjacent material outlet valve The gas sparging head(s) may be connected to a gas control system and sources of compressed carrier gas and one or more volatile substances in a manner as described 20 above in connection to Figure 1. The material (32) passes through the vessel to the material outlet valve preferably in counter-current flow to the volatile substance entrained in the carrier gas. The carrier gas may be removed from the top of the vessel (34) through pressure regulator valve (38) and flue (39) and recycled if desired.

Residence time of the material within the vessel may be varied by adjusting flow rate of the material (32) and/or volatile substance/carrier gas mixture and/or by adjusting vessel (34) height so as to achieve a desired duration of contact between the material and volatile substance/carrier gas mixture or, alternatively, by interposing a screw conveyor system within the vessel with variable rotating speed to control the passage of the material (32) as it passes through the vessel In this configuration, the vessel -12- (34) need not be erected vertically but can be arranged in any position compatible with the angle of repose dictated by the material (32) being treated.

Continuous treatment as shown in Figure 3 may be particularly suitable for grated/shredded cheese, other particulates and leafy materials such as herbs.

Example 1: TREATMENT OF SHREDDED CHEESE In this example, shredded cheese was placed in an evacuable test vessel and exposed to a acetic acid/CO 2 gas mixture for the designated period(s) (ie. 2 x seconds with prior evacuation; 1 x 15 seconds without prior evacuation) with or without prior evacuation of the vessel. The shredded cheese was contained in plastic 10 bags and a degree of pressure was allowed to develop in the plastic bags during treatment. 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 twenty four hours prior to microbiological analysis. The results are provided in Table 1.

As can be seen from Table 1, a substantial reduction in the microbial bioburden of the shredded cheese was achieved both with and without the assistance of evacuation prior to contact with the acetic acid/CO 2 gas mixture.

Example 2: TREATMENT OF FRUIT WITH CARBONIC ACID DIPPING In this example, a twenty gram piece of skinned mango was dipped into an equilibrated aqueous solution of carbonic acid for ninety seconds while a continual supply of food grade carbon dioxide was bubbled through the solution in an attempt to maintain an excess concentration of carbonic acid. The mango piece was treated with volatile carbonic acid in CO 2 carrier gas and held in this gaseous atmosphere at approximately 5'C for ten minutes whilst the aqueous carbonic acid dipping solution equilibrated (pH 4.0 by paper). Following re-dipping of the mango piece for one hundred and eighty seconds, excess water was removed by shaking.

Control and treated samples were stored under identical conditions at approximately 5°C. After three hours the control developed a dark orange colour and syneresis at three days. After three weeks there was very little change in the treated sample. Furthermore, only a slight amount of syneresis was observed after an additional 13- 24 hour storage time (ie. total 3 weeks and 1 day) at ambient temperatures No change in colour nor observable mould growth was seen.

In similar trials with avocado, shelf-life was extended from three hours to sixty six hours; the assessment parameters again being colour and observable mould growth.

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

o.

14 TABLE 1 *0 0@ 0* 0 S 0 50 0 0 0* 0000 0 @0 0 @0 @009 0* @0 0 0* 0 000,

S

0 0S 0 0* 0* Total. %Yeast FOODSTUFF GAS MIX No. of' FLOW EXP. Plate Reduction Mould Reduction FLUSH RATE SEC. Count Count SHREDDED CONTROL CONTROL CONTROL CONTROL 3.61 E+05 CONTROL 5.87E+05 CONTROL

CHEESE

CONTROL 4.56E+05 CONTROL 7.80E+05 CONTROL 2.1 9E+05 CONTROL 8.1 6E+05 CONTROL Mean 3.45E+05 CONTROL 7.28E+05 CONTROL SHREDDED ACETIC

CHEESE

VACUUM/FLUSH

Sample Wt: IOgms Aw 0.86 2 22L/M 10 <10 >99.999 8.00E+00 99.9989 SHREDDED ACETIC

CHEESE

NO VACUUM Sample Wt: IlOgms Aw 0.86 1 22L/M 15 <10 >99.999 <10 >99.999

Claims (21)

1. A method for reducing the viable microbial content of a solid material for human consumption, which is susceptible to microbial spoilage, said method comprising the steps of: entraining a volatile substance in a liquid form, selected from the group consisting of natural food acids, chemical biocides and mixtures thereof, in a stream of a carrier gas to form a gas mixture substantially.free of particles of the volatile substance comprising a major portion of the carrier gas and a minor portion of the volatile substance, and contacting exposed surfaces of the material with the gas mixture for a contacting period of 2 minutes or less during which time 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, 15 the exposed surfaces of the material have a water activity (Aw) of greater than or equal to 0.85; ste wherein said method does not involve, prior to step and/or a step of subjecting the material to a vacuum. 9 S. 20

2. A method according to claim 1, wherein the volatile substance includes a natural food acid.

3. A method according to claim 2, wherein the volatile substance includes -carbonic acid.

4. A method according to claim 2, wherein the volatile substance includes *ooo acetic acid.

A method according to any one of the preceding claims, wherein the volatile substance includes hydrogen peroxide.

6. A method according to claim 2, wherein the volatile substance is selected from the group consisting of carbonic acid, acetic acid, hydrogen peroxide and mixtures of carbonic acid and acetic acid, and carbonic acid and/or acetic acid with hydrogen peroxide.

7. A method according to any one of the preceding claims, wherein the volatile substance is entrained in the carrier gas in saturating amounts.

8. A method according to any one of the preceding claims, wherein the carrier gas is carbon dioxide and/or nitrogen gas.

9. A method according to any one of the preceding claims, wherein the method is conducted continuously. A method according to an one of the preceding claims, wherein the duration of the step of contacting the exposed surfaces of the material with the mixture is in the range of 0.05 to 2 minutes.

S: 15

11. A method according to any one of the preceding claims, wherein the S. contacting period is in the range of 0.15 to 0.5 minutes. 20

12. A method according to any one of the preceding claims wherein at the time of contacting the exposed surfaces of the material with said gas mixture, S 20 the exposed surfaces of the material have a water activity (A)J.of greater than or equal to 0.95.

13. A method according to any one of the preceding claims, wherein prior to the step of contacting the exposed surfaces of the material with said gas a 25 mixture, the exposed surfaces of the material are wetted with up to about w/w of water. *•go

14. A method according to any one of the preceding claims, wherein prior to the step of contacting the exposed surfaces of the material with the gas mixture, an aqueous solution of a volatile substance, which may be the same or different to the volatile substance contained in the gas mixture, is applied to the surface of the material.

A method according to claim 14, wherein the aqueous solution is applied to the surface of the material by dipping or spraying.

16. A method according to any one of the preceding claims, wherein the step of contacting the exposed surfaces of the material with said gas mixture is conducted in a vessel with an over-pressure of up to 3 bar (2250mm Hg) above atmospheric pressure.

17. A method according to any one of the preceding claims, wherein the step of contacting the exposed surfaces of the material with said gas mixture is repeated up to 3 times.

18. A method according to claim 19, wherein each step of contacting the 15 exposed surfaces of the material with said gas mixture is conducted in separate vessels. *0

19. A method according to claim 18, wherein each step of contacting the exposed surfaces of the material with said gas mixture is conducted in a 20 single vessel.

20. A method according to claim 19, wherein between each step of contacting the exposed surfaces of the material with said gas mixture, the vessel is evacuated and/or flushed with a suitable gas. 9*9* S

21. A method according to any one of the preceding claims, wherein the material to be treated is a food, pharmaceutical product or ingredient thereof. Co.. Dated this 4th day of April 2001 Vaporex Ply Limited Patent Attorneys for the Applicant: F B RICE CO