HYDROPHOBIC PACKAGING MATERIAL INCLUDING A SULPHITE SALT

The present invention relates to materials for packaging (hereinafter referred to as "packaging materials") food or beverage products.

The present invention also relates to packaging products, such as containers, that are constructed at least in part from packaging materials. In some embodiments, for example where the packaging materials are in the form of polymeric films , the packaging products are the packaging materials per se.

In particular, although by no means exclusively, the present invention relates to packaging materials that are made from polymers or polymer blends or other materials that are suitable for use as packaging products for packaging food and beverage products or for manufacturing such packaging products.

In this specification the term packaging' refers to containment of food or beverage products both in packaging intended for distribution of food and beverage products to consumers and packaging intended for manufacturing, storing and other steps in the production of food or beverage products .

An example of an application for the packaging materials of this invention is packaging products in the form of retail ^λ bag-in~box' wine casks. Bag-in-box wine casks typically comprise ^λ bladders' that are made from packaging materials in the form of polymeric films and have taps for dispensing the wine in the bladders and are enclosed inside cardboard boxes or tubes that are designed to protect the bladders and hold them in a controlled shape .

Another application of this invention is packaging products in the form of polymeric bags or liners made from packaging materials in the form of polymeric films that are used as part of the wine production process or for the bulk shipping of wine from a winemaking operation to a final market, which may be a different country or continent .

Although the above applications are all examples of packaging products made from packaging products in the form of flexible polymeric films , this present invention is also applicable to packaging products, such as bottles, that are made from packaging materials in the form of rigid blow-moulded or injection-moulded polymeric packaging materials .

Another application of this invention is packaging products in the form of liners of polymeric materials, such as polymeric material liners used to protect the inside of food and beverage cans from corrosion.

Materials used for manufacturing packaging materials comprise, by way of example, polymeric materials such as low density polyethylene, high density polyethylene, polypropylene , ionomers , ethylene and propylene copolymers, polylactic acid or other polyesters, polyamides , vinyl alcohol polymers or copolymers , degradable polymers, or other polymer materials which may be identified as suitable. The materials may further comprise additives which impart further functional properties such as physical property modification, emission of gases or liquids, or absorption of gases or liquids.

The present invention relates more particularly, although by no means exclusively, to packaging materials for food and beverage products in situations where it is desirable or essential to maintain or extend the shelf life of food or beverage products .

The present invention relates more particularly, although by no means exclusively, to packaging materials for packaging food and beverage products that have one or more than one active additive that positively influence the shelf stability of the packaged products .

In one embodiment the present invention relates to maintaining levels of free sulphur dioxide in wine, and the following description of the present invention focuses on this application. However the present invention is equally applicable to other beverage and food products where sulphur dioxide is used as an anti-oxidant, including for example fruit juices and beers .

Sulphur dioxide is routinely added to wine during processing of the wine and filling of packages to preferentially react with any free oxygen in the product to reduce oxidation of the wine and thereby avoid deterioration in the flavour of wine caused by the oxidation of the wine components . However, notwithstanding the benefit of sulphur dioxide, high levels of sulphur dioxide are undesirable because sulphur dioxide can adversely affect the taste of wine.

The sulphur dioxide found in wine exists in two different forms . ^λ Bound' sulphur dioxide is chemically bound to other compounds in wine, such as aldehydes . Free sulphur dioxide is not bound to other compounds , and so is free to react with any oxygen present. There is an equilibrium between the free and bound sulphur dioxide, which depends on many factors including the exact chemical

composition of the wine, and the amount of oxygen present. Sulphur dioxide is not necessarily added directly into wine, but may instead be added in the form of sulphites which break down into sulphur dioxide in the wine .

Oxygen can enter a filled container of wine both during filling wine into the container and also during the storage of the wine in the container. In particular, small amounts of oxygen can diffuse through the packaging materials used to hold the wine, as well as its dispensing features . Over time the sulphur dioxide added with the filled container is consumed through its reaction with the oxygen in the wine. Once the free sulphur dioxide is fully consumed, there will be undesirable oxidation of the wine.

Secondly, when the free sulphur dioxide level decreases to very low levels, bound sulphur dioxide in the product converts to free sulphur dioxide, which releases other undesirable components such as aldehydes to which the sulphur dioxide was formerly bound.

The above considerations place a practical limitation on shelf life of the filled wine container.

There are many commercial advantages in extending the shelf life of a filled wine container, especially if the filled wine container is being exported from one continent to another by sea transport, for example being shipped from Australia to Europe.

It is clear that such a packaging product has a limited period of optimum consumption, related to the period in which the free sulphur dioxide is within certain limits. Although these limits vary with product and batch, it is generally accepted in the art that levels of free

sulphur dioxide between 35 ppm (mg/1) and 15 ppm is the preferred range for commercial acceptability.

The present invention provides the use of active additives in packaging materials , such as polymeric films , which release sulphur dioxide into the packaged products over time and reduce the rate of decrease of free sulphur dioxide in the products over time .

The present invention is based on the realisation that the inclusion of a sulphite salt, and optionally further additives , in one or more than one layer of a packaging material, such as a polymeric film, is an effective a source of sulphur dioxide .

In a case where such a packaging material is used to contain wine, migration of naturally occurring acids from wine into the packaging material causes a reaction that releases free sulphur dioxide into the wine . The rate of release of sulphur dioxide is related to the rate of migration of acids from the product.

The present invention is also based the realisation that the use of an alkaline additive in a packaging material, such as a polymeric film, can provide an additional controlling mechanism for the release rate of sulphur dioxide by regulating penetration of product acids into the packaging material .

The release of sulphur dioxide from a packaging material, such as a polymeric film, through the reaction of calcium sulphite with an acid is disclosed in the prior art.

European patent application EP 0 351 636 discloses a packaging material comprising two sheets of material which are laminated together with a binding

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agent. The binding agent has dispersed therein a sulphur dioxide releasing material such as sodium metabisulphite . An hydrophilic polymer is used to contain the sodium metabisulphite. This invention suffers from the inherent instability of sodium metabisulphite, which has a significant rate of uncontrolled release of sulphur dioxide in storage, and is an occupational health hazard.

International application WO94/10233 discloses a wide range of single and multi-layer materials and polymeric materials which are capable of releasing sulphur dioxide. In this invention the acid is added into the film during its production. This invention suffers from moisture sensitivity, in that storage in a moist environment will trigger the sulphur dioxide release reaction prematurely.

International patent WO2004/052109 discloses a method of releasing and controlling sulphur dioxide release by the use of an hydrophilic polymer which swells upon contact with moisture, a sulphite salt and a latent acidulant. This invention has similar issues to WO94/10233

The present invention is distinguished from this prior art in that it:

a) is not confined to the use of a hydrophilic film, but instead can use modifications of existing commercial packaging materials - hydrophilic materials have a number of inherent disadvantages when used to contain beverages and water containing food and;

b) relies on the natural acids in wine (and other products) to drive the

sulphur dioxide release - since the diffusion of natural acids in a packaging film will be slow, the resulting release of the free sulphur dioxide will be controlled;

c) relies on the migration of acids from the product, and uses thermally stable sulphites, and is totally stable prior to use; and

d) comprises as an embodiment further means of reducing migration of acids from the wine to the sulphite compound, whereby the release of free sulphur dioxide can be optimally controlled.

When referring to a material as being ^hydrophilic' , for example in paragraph (a) above or its opposite, i.e. ^hydrophobic' , it is useful to consider that polymeric materials are neither fully hydrophilic nor fully hydrophobic, but instead have a degree of natural permeability, especially to water vapour. Nonetheless, it is useful for the clarity of this specification to be able to determine if a polymer is hydrophobic or hydrophilic. One means of characterizing whether a material is hydrophilic or hydrophobic is to consider the Water Vapour Transmission Rate (WVTR) of the material when measured under standard conditions. In this patent specification a

^hydrophilic' material is defined as a material with a measured WVTR of greater than or equal to 100 g/m ² .day. In this specification WVTR is measured for a 25 urn thick sample of the material using ASTM F1249 measured at 38° C and 95% relative humidity. Similarly, a hydrophobic' material is defined as a material with a measured WVTR of less than 100 g/m ² .day under the same conditions.

According to the present invention there is provided a hydrophobic packaging material for packaging food or beverage products that includes one or more than one sulphite salt as a source of sulphur dioxide in one or more than one layer of polymeric material or materials that form the packaging material .

A person skilled in the art will be readily able to determine the amount of calcium sulphite to be added to a packaging material in any given situation . The amount of sulphite salt in any given situation depends on the volume of the food or beverage product contained in the filled package .

By way of example, in a situation where the food or beverage product is wine, the level of sulphite added is typically selected to add a given amount of free sulphur dioxide after reaction with the acids in the wine . For example, a wine maker might wish to add a total of 50 ppm (mg/1) of free sulphur dioxide to a wine, assuming a complete reaction of the available calcium sulphite . The wine maker knows that free sulphur dioxide is the excess sulphur dioxide after the total bound sulphur dioxide has reached an equilibrium level, i.e. adding 10 ppm free sulphur dioxide to a wine containing 10 ppm free sulphur will lead to a total sulphur dioxide level of 20 ppm. The wine maker might select a packaging material in the form of a polymeric film to contain 3 litres of wine, and might have selected a 150 mm by 200 mm by 100 mm bladder to contain this wine. This would give a total contact area of 0.13 m2 , or allowing for sealing area a total film area of say 0.14 m2. The wine maker knows that calcium sulphite reacts with acid to create hydrogen sulphite, which in turn breaks down into sulphur dioxide and water. By stoichemetric calculations the winemaker is able to determine that 1 gram of calcium sulphite gives 0.53 grams

of sulphur dioxide. This means that to add 50 mg/1 of free sulphur dioxide to 3 litres of wine requires an addition of around 280 mg of calcium sulphite to the polymeric film. Since there is 0.14 m ² of the polymeric film, the wine maker or packaging engineer needs to add about 2 grams of calcium sulphite per square metre of the packaging film. The bladder used to contain wine might be 35 um thick and have a density of 0.92 g/cm ³ , i.e have a grammage of 32 grams per square metre . Hence a packaging engineer might specify in this context a nominal calcium sulphite content in the packaging material of 6.25%. However this is just an example of such a calculation, and the desired calcium sulphite loading might also depend on other factors such as the planned shelf life of the wine, the purity of calcium sulphite, the efficiency of the manufacturing process, and many other variables. In some cases it might be desirable to target a total sulphur dioxide addition level of greater or less than 50 ppm.

Preferably the amount of the sulphite salt or salts is selected to add less than 200 ppm of sulphur dioxide to the contents of the food or beverage product.

More preferably the amount of the sulphite salt or salts is selected to add less than 100 ppm of sulphur dioxide to the contents of the food or beverage product.

Typically, the amount of the sulphite salt or salts is selected to add less than 50 ppm of sulphur dioxide to the contents of the food or beverage product.

In practice this is likely to lead to a sulphite salt content in the packaging material of less than 25 % by weight.

Preferably the sulphite salt content in the packaging material will be between 5 and 20% by weight.

The packaging material may be a polymeric film.

The packaging material may also be a blow-moulded or an injection-moulded polymeric material, such as used in the construction of bottles .

Preferably the sulphite salt or salts is selected from sulphite salts that are thermally stable at or above extrusion temperatures of the polymeric material or materials and are chemically inert in the presence of the molten polymer .

More preferably the sulphite salt is a calcium sulphite.

The above-described packaging material may include at least one layer (hereinafter referred to as a ^λ sealing layer') that has acceptable heat sealing properties and can be used to help form the packaging film into a liquid tight container .

The sealing layer may also be a sulphite salt- containing layer .

The polymeric material in the layer or layers of the packaging material may be any polymeric material that is chemically stable in the presence of the sulphite salt or salts . Examples of these polymeric materials are a polyolefin or a polyester.

The packaging material may include an alkaline material to control the release of sulphur dioxide from the packaging material .

Preferably the alkaline material is adapted to react with migrating acids in a packaged product, thereby

effectively reducing the ability of the acids to react with the sulphite salt or salts and produce sulphur dioxide .

Preferably, the alkaline material is a metal oxide .

More preferably the metal oxide is an aluminium oxide .

The alkaline material may be added to any one or more than one layer in the packaging material that contains the sulphite salt or salts, such as the calcium sulphite, to control the release of sulphur dioxide.

Alternatively, the alkaline material may be added to any one or more than one layer in the packaging material that does not contain the sulphite salt or salts , such as the calcium sulphite.

As an example, the alkaline material may be added into the layer or layers of the packaging material, such as a polymeric film, adjacent to the wine and the sulphite salt or salts may be added to an inner layer or layers of the packaging material, which may be the same or different layer or layers. In this example, it is likely that the degradation of the sulphites will be delayed until the alkaline material is largely consumed. The optimization of the addition of the alkaline material will hence provide a winemaker the potential to ^λ fine-tune' the release of the additional sulphur dioxide from the sulphites in the sulphite layers .

Alternately, the alkaline material may be blended into one or more than one of the layers of the packaging material to reduce the rate of sulphur dioxide release by co-reacting with acids migrating into the layer or layers .

Preferably the alkaline material has a concentration not exceeding 25% of the total weight of the packaging material .

More preferably the alkaline material has a concentration not exceeding 15% of the total weight of the packaging material .

It will be understood from the above that separate layers comprising alkaline salts, combined layers of alkaline salts and sulphite salts and layers comprising only sulphite salts may be arranged in many ways to control sulphur dioxide release and all such arrangements lie within the scope of the present invention.

It will further be understood from the above that different polymer types and thicknesses will provide different rates of acid migration, and selection of polymers, grades and thicknesses of layers either as sulphite-containing layer or layers, alkaline-containing layer or layers , or simple polymer layer or layers to assist in controlling acid migration, are within the scope of the present invention .

It will also be understood that the hydrophobic!ty of the packaging material of the present invention is important because a material that is hydrophilic, i.e. has an excessive water vapor transmission rate (^WVTR'), would not work as intended as the reaction between the acids in the wine and the sulphur dioxide producing salt would be at an excessive rate, leading to an uncontrolled and excessive buildup of free sulphur dioxide in the wine .

In situations in which the packaging material is formed by extrusion of a single layer or by co-extrusion

of multiple layers , the sulphite salt or salts and the alkaline material may be blended with the polymeric material or materials prior to extrusion or co-extrusion.

The layer or layers of the packaging material of present invention may comprise additives in the form of concentrated dispersions (or masterbatch) of the active component in suitable polymers permitting selection at manufacture of blend rations and thus final material performance.

According to the present invention there is provided a packaging product, such as a container, for packaging products , such as food or beverage products , that includes the above-described packaging material, such as a polymeric film, with a sulphite salt addition and optionally an alkaline material addition so as to control the release of sulphur dioxide from the packaging product.

The packaging material may be a polymeric film.

The packaging material may also be a blow-moulded or an injection-moulded polymeric material, such as used in the construction of bottles, closures, tubs, cups and the like.

By way of example, the container may be made from a packaging material in the form of a flexible polymeric film, such as a "wine cask" or ^M bag-in-box" cask, or be used for the manufacturing or fermenting of the food or beverage .

The ability of packaging material manufactured according to this present invention to release free sulphur dioxide in a controlled manner into wine was investigated in the following experiments .

Experiment One - Laboratory experiment

Evaluation

Discs of polyethylene film compounded with 5% w/w

CaSO ₃ were placed in 20 iriL headspace vials and filled with recently purchased commercial riesling wine .

Control vials were also filled with the wine, but no disc was added. Sodium metabisulphite was added to both samples at a level designed to add the equivalent to an additional 50 ppm of free sulphur dioxide for both the test samples and the corresponding blanks .

The additional free sulphur dioxide was added as the filling of the vials would unavoidably add oxygen into the wine, and the applicant was trying to replicate the normal filling of wine, where sulphites would be added into the wine to react with this oxygen, as discussed above. In practice, it turned out that this led to higher than normal levels of measured free sulphur dioxide, due to the presence of the unconsumed sulphur dioxide remaining from the original commercial filling of the wine.

The vials were stored at 23 ⁰ C and 50% humidity.

The free sulphur dioxide content was determined at 0, 1, 3, 7, 14 and 28 days via the aspiration method ¹ with the samples and blanks analysed in duplicate.

Results and discussion

^{1 2} Iland, P., Bruer, N., Edwards, G. Weeks, S. and Wilkes, E. 2004 Chemical analysis of grapes and wine: techniques and concepts. Patrick Hand Wine Promotions Pty Ltd. pp 55.

The results of the above experiment are summarized in Figures Ia and Ib.

Figure Ia shows a plot of the level of free sulphur dioxide in the wine over the test duration. The figure shows that the wine began to lose free sulphur dioxide immediately, possibly due to reaction with the oxygen added into the wine during the filling of the vials . There is only a small difference between the measured free sulphur dioxide levels for the first two weeks, but a large difference after 28 days.

Figure Ib shows a plot of the difference between the levels of free sulphur dioxide in the wine in the no disc and disc samples. The figure suggests that the sulphite discs are adding an increasing amount of free sulphur dioxide in a controlled manner during the term of this experiment

Experiment 2 - Pilot extruder experiment

The experiment was an attempt to replicate the laboratory results of Experiment 1 on a 3 layer pilot extruder. Food grade calcium sulphite (CaSO ₃ ) and aluminium oxide (AI ₂ O ₃ ) were blended into the layers of commercial grade polyethylene (PE) at the following loadings :

• Sample A: 20% CaSO ₃ in the middle layer

• Sample B: 10% CaSO ₃ blended in all three layers • Sample C: 10% CaSO ₃ and 10% Al ₂ O ₃ in all three layers

• Sample D: 20% Al ₂ O ₃ blended in the contact layers (contact layer with the wine) and 20% CaSO ₃ in the middle layer

• Conventional : seal layer of conventional wine bladder made from a 35 um polyethylene material

Evaluation

An area of each film selected to give a similar specific contact area to a 3L bag in box wine bladder were added into to individual 20ml headspace vials. These vials were filled to the brim with riesling wine and capped.

As with Experiment 1 , sufficient sodium metabisulpite was added to this wine to add an estimated 50ppm of free sulphur dioxide to the wine, and capped.

All the filled vials were stored in dark at ambient conditions at 23 ⁰ C and 50% RH.

The free sulphur dioxide content of the wine was measured by the aspiration method on a weekly basis for 6 weeks .

Results and Discussion

In general, the experiment found that as the wine aged the measured free sulphur dioxide content reduced.

The measured free sulphur dioxide concentration in the packed wine is shown in Table 1.

Table 1 shows that:

• All trial samples had higher measured levels of free sulphur dioxide than the conventional film, although the differences were not that large after 44 days.

• Sample B (10% calcium sulphate in all three layers) gave the highest measured free sulphur dioxide levels than remaining three trial materials . It should be noted that calcium sulphate is present in all three layers of this film.

• There were not large differences between the samples containing aluminium oxide and the samples with only calcium sulphate present. • Similarly the level of calcium sulphate or aluminium oxide addition did not appear to greatly affect the results .

• Three of the samples showed an apparent large reduction in the measured free sulphur dioxide levels after 38 days, which seemed to disappear after 44 days . This have been because the aspiration method requires the fresh preparation of titration chemicals for each day's testing, and this can lead to errors when comparing data between test days .

In some respects , these results were not as positive as the laboratory results of Experiment 1. However, the results should be considered in the context that:

• This was only the first pilot trial, and scaling up from laboratory to pilot conditions always brings a number of confounding factors .

• Subsequent elemental SEM analysis of the samples showed limited disperson of the calcium sulphite and aluminum oxide within the film samples . This may affect the results .

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Many modifications may be made to the present invention described above without departing from the spirit and scope of the invention.