The present invention relates to packaging films for the food and flower industry, more particularly to packaging films suitable for packaging materials which respire.

Background of the Invention

Various packaging materials have been proposed for preserving respiring biological materials, such as foods and flowers, after they are harvested or produced. One means for so doing is to package the biological materials in "modified atmosphere packaging" (MAP) or "controlled atmosphere packaging" (CAP). Such packaging is designed to modify the levels of carbon dioxide (Cθ2), oxygen (02) and/or other gases to which the packaged articles are exposed, in order to retard deterioration. A number of theories have been proposed as to the effect varying the levels of these gases has on the rate of decomposition of respiring biological materials (c.f. "Storage of Common Mushroom under Controlled Atmospheres", Briones et al., International Journal of

Food Science and Technology. (1992) 27, 493-505; "Modified Atmosphere Packaging of Common Mushroom", International Journal of Food Science and Technology. (1993) 28, 57-68; "Recent Developments in the Processing of Fruit and Vegetables in France", Varoquaux, The European Food and Drink Review.

Autumn 1993; "Ready-to-use Fresh Fruits and Vegetables", Varoquaux, Rev. Gen. Froid. July 1991).

Certain υlymer films have been proposed for such applications: Micro-perforated polypropylene films are commonly used, but have the disadvantage that they do not function as a barrier to certain microorganisms. C.f. also US Patent No 5,254,354 wherein

films are described as being made from a polymer having a side- chain crystallizable polymer and a permeability which increases by a factor of greater than 2.5 in response to a 10°C temperature increase; US Patent 4,842,741 describes a heterogeneous film having a porous core layer and nonporous outer layers, and containing a filler; FR 2 351 877 describes film of polyurethane suitable for packaging meats and cheeses, though does not mention modified or controlled atmosphere packaging.

It has now been found that homogeneous packaging films made from block copolyether esters and block copolyether amides are able to create particularly desirable modified atmospheres for the packaging of respiring biological materials.

Summary of the Invention

Accordingly, the present invention relates to the use of a homogeneous packaging film of a block copolyether ester or a block copolyether amide to package an actively respiring biological material such as a food product or a flower, and to the resulting packaged article.

Detailed description of the Invention

As used herein, certain terms have the following meanings.

"Biological materials which respire" refer generally to fresh fruits, vegetables and flowers, and to dairy products such as cheeses.

Particularly good results can be obtained with the packaging films of this invention when used to package fruits and vegetables, such as tomatoes, mushrooms, green beans, lettuce, beansprouts, figs, apricots, strawberries and raspberries.

The particular packaging films of the present invention, i.e., block copolyether esters and block copolyether amides, are known per

se, and commercially available. As films, these polymers have thicknesses ranging from 10 to 120 microns, and demonstrate the following permeabilities at 1 atm pressure, 100% humidity, and 23 °C: 02 permeability of <25,000 ml/m^-day, preferably < 15, 000 ml/m ² -day, suitably from 3,000 to 20,000 ml/m ² -day; Cθ2 permeability of >75,000 ml/m^-day, more preferably >100,000 ml/m^-day, suitably from 85,000 to 1,000,000 ml/m^-day. Furthermore, the films of the present invention will be homogenous and do not require a filler (unlike those films described in US Patent 4,842,741).

Preferred block copolyether esters are segmented elastomers having soft polyether segments and hard polyester segments (c.f. U.S. Patent No. 4,739,012), available from the DuPont Company under the name Hytrel® .

Suitable block copolyether amides for use in the invention are described in US Patent 5,069,955 and are available under the name Pebax® from Elf Atochem.

The packaging films according to the present invention may be free-standing, or may support or be supported by additional films in multilayer film constructions. Such additional films will be made of highly porous materials, such as paper or the films described in the patent publications mentioned herein.

The biological materials can be packaged in any of a variety of known styles. For example, the packaging may be made 100% from the films, or the films may comprise a part of the packaging. In the latter case, a support which holds the biological matters can be used, which is then sealed shut with the packaging film of the present invention. Such support may be made from any conventional material which is a gas barrier, such as polypropylene, polystyrene, etc.

Alternatively, the packaging material of the present invention can be formed as a "window" in a sealing film made from another

material. In this case, the film for sealing the support can be of a conventional gas barrier polymer, such as polyethylene, polyester, etc., into which is formed (by conventional techniques) a window of packaging film of the present invention.

The only governing feature of any such packaging design is that sufficient surface area of packaging film for the present invention be used to provide modified or controlled atmosphere packaging. The specific amount of surface area will, of course, depend upon the size and design of the package, and the type of biological material that is packaged.

Examples

MATERIAL AND METHODS

1. Raw material:

Cultivated mushrooms are obtained from Ferme de la Gontiere

(France). 200 to 250 grams of whole mushrooms, with bases removed, are evaluated for organoleptic qualities (color and velum opening) and subsequently stored in bags, having a surface area of 800 cm ² , made from various plastics having different permeabilities.

2. Reference films:

A film of oriented polypropylene (OPP) and films "P+" from

Sidlaw Packaging, U.K., are used, having the permeability grades listed in Table 1.

Table 1 : Permeability of reference films

Ref. Film 02 Permeability Cθ2 Permeability

(ml/m ² .day.atm) (ml/m .day.atm)

OPP 900 4000

P+ 5000 5000 9000

P+ 10000 10000 14000

P+ 25000 25000 29000

P+ 50000 50000 54000

P+ 100000 100000 104000

P+ 200000 200000 204000

3. Hytrel® Films studied:

G-4078, G-3548W, HTR-8206, G-4778; all commercially available grades from the DuPont Company.

4. Conservation conditions:

Temperature: 8-9 °C

Sampling every second day up to the 8th day.

5. Organoleptic evaluation:

Evaluation of the velum opening through visual observation and positioning on the BURTON simplified scale (c.f. LOPEZ-

BRIONES et al.).

closed velum: normal appearance at harvesting stretched velum: velum is fully attached to stem but begins to stretch

torn velum: mushroom starts to separate from the stem and is torn in several places open velum: velum has completely separated from the stem

6. Evaluation of the color of the mushrooms:

Reflectometric measuring of the color with a HUNTERLAB COLORQUEST apparatus.

a) measurement of the external color: 3 measurements on the top of 10 carpophores

b) measurement of internal color: after removal of a 5 mm top section.

Interpretation in the CIE LAB system. The L parameter (luminance) is noted down to evaluate the darkening.

RESULTS

1. Permeability measurements:

1.1 Permeability to 02 and Cθ

The 02 and C02 permeabilities of Hytrel films can be calculated under actual conditions of use from measurements of the level of 02 and C02 in the bags at

8 °C, saturated humidity conditions (internal face of the film) after 2, 4 and 6 days. These are reported in Tables 1 and 2.

Table 1 : 0? _^ permeability of Hytrel® films

Table 2: Cθ2 permeability of Hvtrel® films

2. Effect of the film on the organoleptic qualities:

2.1 Effect on the opening of the velum:

It is known that the C02 prevents the opening of the carpophores. Thus, the most impermeable films prevent the ripening of the mushroom (for mushrooms packed in the films OPP, P+ 5000 and P+ 10000: 100 % of velum stretch after 6 days of conservation at 8 - 9 °C). The mushrooms packed in the films P+100000 and P+ 200000 behave like those packed in Hytrel® films (about 20 % of velum tears).

2.2 Effect on the color:

After 2 days of conservation, the external color of the mushrooms packed in Hytrel® films is statistically lighter (average L less than 91 ) than the one of mushrooms packed with oriented polypropylene film (L increases from 86 to 90 according to the permeability of the film). The internal color is also much more attractive for the mushrooms packed in Hytrel® films.

The positive effect of Hytrel® films on the external color of the mushrooms is apparent until the sixth day of conservation; afterwards, the improvement in color is less apparent. However, mushrooms packed in Hytrel® retain the advantage that even beyond the sixth day of conservation they do not become slimy; mushrooms packed in oriented polypropylene, in contrast, ferment and become slimy.