AU2376492A - Flexible films for modified atmosphere packaging - Google Patents

Description

FLEXIBLE FILMS FOR MODIFIED ATMOSPHERE PACKAGING

This invention relates to flexible polymeric films useful in the modified atmosphere packaging of fresh produce such as fresh fruits, vegetables and flowers. The invention includes polymeric films in the form of a suitable package that can control the atmosphere surrounding fresh produce in such a way that the post-harvest life of the produce is extended. The films of the invention contain a glycerolate.

Background of the Invention

Deterioration of produce after harvesting involves many complex factors, among which oxygen, carbon dioxide, water and ethylene have been identified as playing important and interrelated roles in the ripening and decomposition process. When produce is enclosed in plastic film, respiration continues, consuming oxygen and producing carbon dioxide.

In general, produce is adversely affected by low concentrations of oxygen. The relative concentration of oxygen and carbon dioxide is also important. The concentration of these gases will vary according to the selective permeability of the polymer film.

For each produce type there is an optimum range of concentrations of C0₂ and 0₂ which retard the respiratory rate and improve the quality to the greatest extent under storage conditions. Although high concentrations of C0₂ are sometimes beneficial (e.g. strawberries and mushrooms) low 0₂ concentrations have deleterious effects on the quality of the produce. The relative flow of the two gases through the film under storage conditions and the type of produce determine the final composition of the atmosphere. Ethylene is also known to advance the onset of an irreversible rise in respiration and ripening.

The action of low levels of gaseous ethylene as maturation hormone is well established. In particular, addition of low levels (ca 1-10 ppm) of ethylene to produce, stored under controlled atmosphere conditions is an established process to induce the onset of ripening. The reverse procedure, that of removal of ethylene from stored produce, has also been commonly practiced over many years. Methods for removal of ethylene have generally centred around scrubbing processes, in which the gas was reactively scrubbed, out of a recirculating atmosphere, for example by bubbling through potassium permanganate solutions. However, it will be appreciated that the concentration of ethylene within a package may also be effectively reduced by using a packaging material of appropriate permeability. As the concentration of ethylene in the atmosphere outside the package is practically nil, diffusion of ethylene through the packaging material will essentially be a one¬ way process that permanently removes ethylene from the atmosphere within the package.

On the other hand, diffusion of carbon dioxide and oxygen through packaging films is a complex two-way process that is only imperfectly understood. PRIOR RELATED APPLICATION

In our earlier Australian patent application 81642/91, the entire disclosure in which is by this reference incorporated into the present specification, we have described and claimed a flexible gas-permeable polymeric film useful in the modified atmosphere packaging of fresh produce, characterised in that the film incorporates an ethylene reactive agent, a preferred agent being sodium permanganate.

SUMMARY OF THE INVENTION

We have now found that the relative flow of carbon dioxide and oxygen through packaging films can be affected in a manner beneficial to the storage life of fresh produce packaged therein by the incorporation of certain materials into the said films. The materials are conveniently added to the initial polymer before extrusion.

In accordance with the invention, the additives used are one or more metal glycerolates, preferably zinc glycerolate. The film may be any suitable flexible polymeric film, for example polyethylene, polypropylene, polyvinyl chloride and other well-known films suitable for packaging, and preferably contain fillers, for example silica, alumina, magnesium oxide and/or pumice.

The glycerolate may be present in the film in an amount from 0.025 to 0.4% by weight. In a preferred embodiment of the invention, the glycerolate is incorporated into films which also contain one or more of the agents disclosed in our above mentioned Australian application 81642/91. Although we do not wish to be limited by any hypothetical or postulated mechanism for the observed beneficial effects, it is believed that the metal glycerolate in combination with the filling materials has an effect on voiding and pore formation of the microporous polymer film.

Example 1

A masterbatch was prepared with low density polyethylene in which pumice and zinc glycerolate were added so that the loadings were 20% and 1% respectively. Before extrusion the masterbatch was then combined with linear low density polyethylene so that the final composition of the blown film contained about 4% pumice and .2% zinc glycerolate.

Examples 2 and 3

In a similar manner to Example 1, films were prepared containing:

In a similar manner to Example 1, a film was prepared containing 0.2% sodium permanganate, 0.1% glycerolate and 2% pumice. PRODUCE TRIALS

Trials with fresh produce have shown that the films of the invention and particularly those described in the foregoing examples are satisfactory for the storage of broccoli and other produce with similar respiratory rates. In particular, freshness of broccoli and cauliflower wrapped in these films was maintained under storage conditions of about 4°C for periods of up to 50 days.

Claims (8)

CLAIMS :

1. A flexible gas-permeable polymeric film useful in the modified atmosphere packaging of fresh produce, characterised in that the film incorporates a glycerolate.

2. A film according to claim 1 in which the glycerolate is a metal glycerolate.

3. A film according to claim 1 in which the glycerolate is zinc glycerolate.

4. A film according to claim 1, also incorporating a permanganate salt.

5. A film according to claim 1, which is a polyethylene film incorporating zinc glycerolate and sodium permanganate.

6. A film according to any one of claims 1 to 5, also incorporating a filler such as silica, alumina, magnesium oxide and/or pumice.

7. A film according to claim 1, which is a polyethylene film incorporating about 0.2%wt zinc glycerolate and about

4%wt pumice.

8. A film according to claim 1, substantially as hereinbefore described in the Examples.