WO2017188906A1

WO2017188906A1 - Packaging film for packing fresh fruits and vegetables under modified atmosphere

Info

Publication number: WO2017188906A1
Application number: PCT/TR2017/050157
Authority: WO
Inventors: Gurbuz GUNES; Fatma Seniha GUNER; Deniz TURAN
Original assignee: Istanbul Teknik Universitesi Rektorlugu
Priority date: 2016-04-26
Filing date: 2017-04-22
Publication date: 2017-11-02
Also published as: DE112017000128T5; JP2019515055A

Abstract

The invention is related to the packaging of fresh fruits and vegetables in the food industry. The present invention describes the synthesis of polyurethane films having different compositions by using monomers having distinct physical and chemical properties and the method of transforming them into films by using the casting method and the hot press method, and the packaging films produced by this method. Additionally, the use of this film is also described.

Description

DESCRI PTI ON

PACKAGI NG Fl LM FOR PACKI NG FRESH FRUI TS AN D VEGETABLES UNDER

MODI Fl ED ATMOSPHERE

TECHNI CAL Fl ELD

The invention is related to the packaging of fresh fruits and vegetables in food industry. The present invention describes the synthesis of polyurethane films having different compositions by using monomers having distinct physical and chemical properties and the method of transforming them into films by the casting method and the hot press method, and the packaging film produced by said method and the use of this film.

PRI OR ART

Modified Atmosphere Packaging (MAP) refers to changing the composition of the atmosphere around the food product inside the package. Modified atmosphere packaging allows the control of chemical, enzymatic or microbiological reactions and therefore prevents or reduces the effect of the factors which will cause deterioration of the product.

The accomplishments obtained from the studies relating to Modified Atmosphere Packaging (MAP) of fresh fruits and vegetables are limited to the capabilities of available packaging material. While packaging materials having a high gas barrier feature is required for many food products, materials having particular gas permeability (breathable) are required in the packaging of fresh fruits and vegetables. Moreover, the exposure of fresh fruits and vegetables packed under Modified Atmosphere (MA) to ambient temperature after the cold chain has been broken during storage and marketing causes the inner package stability MA to deteriorate and depending on this, the product quality and shelf life is affected adversely. This results from the fact that the temperature and the breathing rate increase more, relative to gas permeability. In this context, the heat sensitivity of the gas permeability of the present commercial packing materials is insufficient. Packing materials whose gas permeability increases with heat, in a similar level to the breathing rate of fruits and vegetables can eliminate this problem.

Looking at the polymeric material applications existing in the packaging field, the most commonly used polymer for the MA packaging of fresh fruits and vegetables is polyethylene. However, by co-processing (co-extrusion) or combining (lamination) different materials l having distinct features, packaging materials having mechanical or optical features have been obtained. Commercial films such as Elvax^® (ethylene vinyl acetate and low density polyethylene (LDPE) based), K-Resin^® (styrene butadiene block copolymer), Attane^® (LDPE octane copolymer) and the Affinity^® series (polyolefin octane copolymer) can be given as examples to these applications. Micro perforation is another method implemented in order to obtain gas permeability of desired levels in packaging fresh products. In this method, perforations are made whose size (20-200 μιτι) and number per unit area varies relevant to the product and package and the permeability of the material is increased in this way. For the solution of the problem of exposure to high temperature and the dependant deterioration of stability MA in fresh fruit and vegetable product MAP, a limited number of studies and systems have been encountered.

In the master's thesis of Mirey Bonfil; polyurethane films having biomedical purity such that they have different castor oil/polyethylene glycol ratios and different polyethylene glycol average molecular weights have been prepared using polyethylene glycol, castor oil, hexamethylene diisocyanate and 1,4-butanediol, without using catalysers and solvents.

In the article of Mirey Bonfil et al. polyurethane films having biomedical purity such that they have different castor oil/polyethylene glycol ratios and different polyethylene glycol average molecular weights have been prepared using polyethylene glycol, castor oil, hexamethylene diisocyanate and 1,4-butanediol, without using catalysers and solvents. In the article of Hande Madra et al. oil-based polyurethane synthesis is described.

In the patent document number WO 2014138218A1, the production of isocyanate-based polyurethane adhesive is described. These polyurethane adhesives are used in food packaging.

None of the above described publications mention the use of said films during packaging of fresh fruits and vegetables.

Forming optimum MA conditions containing gas components close to critical 0₂ and C0₂ ratios at the cold chain package headspace, typical of the product in the MAP of fresh fruits and vegetables, and maintaining the stability of the same until the consumption (during transportation, storage, marketing and consumption) is intended. The most important parameters in forming the inner package stability MA condition are, the atmospheric condition of the product and the breathing rate at heat and the gas permeability (02 and C02) of the package material used. Accomplishments obtained in the studies related to MA packing of fresh fruit and vegetables are limited to the capabilities of the present package materials. While package materials having high gas barrier features are required for many food products, materials having particular gas permeability (breathable) are required for the packaging of fresh fruit and vegetables. Gas permeability values of some packaging materials are given in Table 1.

Table 1 . Gas permeability of some package materials

Polymer Gas permeability [cm (m day atm)^" Water vapour permeability

25 °C, 25 μπι film ; [g (m² day) ¹] ;

Low density 7.700-77.000 3.900-13.000 6-23

polyethylene (LDPE)

High density 3.900-10.000 520-4.000 4-10

polyethylene (HDPE)

Polyvinyl chloride 450-8,000 150-2,200 30-40

(PVC)

Polypropylene (PP) 7,700-21,000 1,300-6,400 4-11

Polystyrene (PS) 10,000-26,000 2,000-7,700 100-150

Polyurethane (PU) 7,000- 25,000 800- 1,500 400-600

Polyamide (Nylon) 150-190 40 84- 3,100

Micro perforated film > 15,000 - -

Gas permeability of polyethylene can be insufficient for fresh fruit and vegetable products having high breathing rate. It is necessary to develop new packaging films having high gas permeability. Moreover, as the product breathing rate and packaging material barrier features are affected from environmental features (temperature, humidity) on different levels this negatively affects the stability MA targeted inside the package. Taking the storage, transportation and sale conditions for fresh fruits and vegetables into consideration, it is seen that the cold chain is broken and the product is exposed to normal ambient temperatures. In such a case, the breathing rate increases substantially together with heat. Change of the breathing rate depending on temperature is generally expressed by Qi₀ value standing for the reaction rate observed at 10°C temperature increase. In fresh fruits and vegetables, for every 10°C temperature increase, the breathing rate increases 2 - 3 fold (Table 2). Changes in temperature also affect the permeability of the package along with the breathing of the product. Although there is no detailed information as to the heat sensitivity of the gas permeability of packaging materials in literature, gas permeability Qi₀ values of some packaging films are given in Table 2 (Exama et al., 1993).

Table 2.Qi₀ values of 0₂ and C0₂ permeability of some packaging films and breathing rates of some fruits and vegetables

Upon investigation of these values, it is seen that gas permeability Qi₀ values of the gas permeability of the present packaging materials are lower than the breathe rate Qi₀ values of many fresh fruits and vegetables. If the product breathing rate is higher than breathing rate of package permeability; this causes the reduction of 0₂ inside the package and increase of C0₂. In such a case, physical deteriorations take place as a result of the anaerobic fermentation and C0₂ damage depending on the low 0₂ first and the high C0₂ inside the package.

The micro perforation technique is another method implemented in order to obtain the desired level gas permeability in packaging fresh products. However, as micro perforated films, allow the passage of C0₂ and 0₂ at the same level in contrary to normal plastic films, it is not suitable to use these films, for products which are damaged by high C02 values such as green leafy vegetables, apples or pears.

Covering the pores perforated into the packages by wax makes gas permeability exchange irreversible. That is to say, gas permeability cannot return to its former state when the temperature is returned to the cold chain again.

In the heat sensitive packaging material developed by Landec Intellipac, it is stated that as a result of the change in the crystal structure with temperature increase, the increase in gas permeability is 2,5 with the 10°C increase between 0 - 40°C and even though the temperature increases in many fresh fruits and vegetables which are packed with this material, stable headspace atmosphere is obtained (EP0560901B1 and WO1992010414A1). The field of usage of this material remained limited due to its weak physical properties. BRI EF DESCRI PTI ON OF THE I NVENTI ON

Some of the advantages that are obtained by means of the invention can be listed as, the synthesized polyurethane films have high oxygen, carbon dioxide and water vapour permeability, the temperature-dependant permeability is changed 2,8 fold at room temperature by an increase of 10°C in the range of 0-40°C and these values are parallel to the breathing rate increase of fresh fruits and vegetable products, synthesizing is possible using natural sources such as castor oil and without using catalysers or solvents, these films are inert and stable in chemical terms, they are concordant with the legal regulation related to the materials contacting the food and they have sufficient mechanical force.

DESCRI PTI ON OF THE Fl GURES

Figure 1. DSC thermogram of Film A.

Figure 2. FT-IR spectrum of Film A after (a) and before (b) the reaction.

DETAI LED DECSRI PTI ON OF TH E I NVENTI ON

Polyurethane films having different formulations have been synthesized by the single step mass polymerization method without using a catalyser or solvent. Polyurethanes are generally formed as a result of the condensation reaction of a diol group with a diisocyanate group (0=C=N-R-N=C=0)by the successive combination with a urethane bond (-CO-0-NH-). They are also block copolymers composed of soft and hard areas. Polyethylene glycol (PEG) chosen as the polyol source is a polyether and it is used due to reasons such as having low transition temperature, good tensile strength, being hydrophilic and providing non-toxic deterioration products. Soft parts composed of polyols provide polyurethane elastomeric features. The hard parts formed by diisocyanates are efficient in forming cross bonds. Castor oil (HY) has been used as a vegetable oil based cross bond since it is cost-efficient and easily obtained and it is efficient in the formation of the hard parts in the polymer together with the chain lengthened The subject of the invention Film A (PU1500-50-40) has been synthesized using PEG 1500 g/mol, 50% castor oil and 40% 1,4-butanediol. In order to remove the humidity which can stop the reaction before the preparation of the reaction mixture in the Film A synthesis from the materials used, PEG 1500 g/mol has been liquefied in the rotary evaporator between 90-95°C under vacuum for 6 hours. Moreover, HY has been kept under vacuum for 1 night at 80°C and 1,4 butanediol (BDO) at 50°C. In order to prepare the reaction mixture, firstly, PEG and HY which are the source of polyol were stirred at 90-95°C in the rotary evaporator until a homogenous mixture is obtained and then the stirring was continued after the addition of the chain lengthener BDO. The prepared reaction mixture was transferred into a three neck reaction flask and stirred at 50°C under nitrogen atmosphere. 1,6-hexamethylene diisocyanate (HDI) was added to the reaction medium slowly so an amount of isocyanate equivalent to the hydroxyl group in the mixture is present. The mixture was poured into glass petri dishes after being stirred at 300 rpm for 4 minutes and it has been left to wait at 80°C for 24 hours, in order to complete the polymerisation reaction. Thermoplastic films have been produced successfully with the casting method and 100 pm thick films have been obtained by hot pressing at 180°C at 7 kg/cm2 pressure. Results obtained in relation to the invention and their significance: gas permeability and heat sensitivities obtained in relation to Film A are given in Table 3.

Table 3.Variable values varying depending on the temperature and humidity of 100 pm thick LDPE studied as reference material of the 100 pm thick Film A has been given below.

According to the data in Table 3, the oxygen permeability rate of the obtained Film A is 3218 ml/m2.day.atm at 23°C with 0% relative humidity and 5235 ml/m2.day.atm at 98% relative humidity. The reason behind this humidity-dependant increase is the existence of polar groups in the structure of the polymer film. The oxygen permeability rate of Film A is 2 fold at 0% relative humidity from LDPE which is a commercial film and approximately 4 fold more at 98% relative humidity. The purpose of conducting the analysis at high relative humidity is that the fresh fruit and vegetable products that breathe, represent the packaging atmosphere better, in comparison to the standard 0% relative humidity at which the measurements are taken. According to the results, Film A may be more appropriate for the fruit and vegetable products that have high breathing rate.

Carbondioxide permeability rate of Film A is approximately 10 fold more compared to the LDPE, which is a commercial film, at 98% relative humidity (Table 3). Selective permeability (β= PC02/P02) of Film A is 15 at 23°C temperature and 0% humidity and 17 at 98% humidity. This value is very high in proportion to the other polymeric films and can be an ideal packaging material for the products that are very sensitive to Carbondioxide, such as leek and green pepper.

Table 4. Qi₀ values of 02 permeability of Film A

For the oxygen permeability of Film A, Qi₀ value is 2,8; which is close to the room temperature in the range of 0-40°C at 0% humidity (Table 4). This value can be increased by changing the PEG molecular weight and castor oil percentage. Moreover, it is two times higher in comparison to LDPE, which is a commercial film. A material whose heat sensitivity is higher in comparison to the prior inventions and Qi₀ values closer to the fruits and vegetables have been obtained.

Activation energy (Ep) for the oxygen permeability of Film A is 63 kJ/mole at 23°C(Table 3). This value is closer to the breathing activation values (65 kJ/mole) of products having high breathing rates such as strawberries; and is higher than the Ep values of commercial films. According to the results, the obtained material has better potential for packaging fresh fruits and vegetables depending on high gas permeability and heat sensitivity.

Table 5. Water vapour permeability rate and humidity absorption value of Film A having a thickness of 100 μιτι Humidity absorption of Film A reaches 20% at 25°C temperature and 98% relative humidity (Table 5).Water vapour transition rate is 100 times more compared to LDPE values in Table 1. Thus, Film A can prevent condensation of the undesired inner package water vapour without perforations for fresh products sensitive to humidity.

The melting temperature of the crystal region in the structure of Film A can be shown as the changing point of the entire gas permeability. In Figure 1, the DSC chart of Film A, the melting peak which is 24°C can be seen. This temperature can be obtained at the desired temperature in the range of 15-40°C by changing the PEG molecular weight, castor oil and chain lengthener percentages.

According to the FT-IR spectra results in Figure 2, all monomers have been used up during the polymerization and the characteristic peak of polyurethane was observed at 3323 cm-1. In addition, its use as the food package was found to be suitable since all of the total migration results in distilled water, acetic acid, ethanol and isooctane is lower than 10 mg/dm2 (Table 6). Moreover, 1,4-butanediol peak was not encountered at GC peaks in synthesized films. The migration amount specific to 1,4-butanediol was found to be within legal limits as < 5 mg/kg. According to the results, the films are usable as food packages.

Table 6.Total migration results of Film A having a thickness of 130pm obtained by hot pressing

According to the TGA results, the obtained films show thermal stability up to 300°C. This shows that the films can be commercially processed by extrusion as well as hot press.

The maximum tensile strength of Film A was calculated as 2,08 MPa, having a maximum extension of 7,9%. Young's modulus (E) obtained from the ratio of tension to the deformation is 100 MPa. As a result, a material was obtained, having mechanical elastic resistance close to LDPE (190 MPa) or to rubber (10-100 MPa).

Claims

1. Use of the film comprising PEG 1500 g/mol, 50% castor oil and 40% 1,4-butanediol in packaging fresh fruits and vegetable products.

2. Use according to claim 1, wherein the oxygen permeability rate is 3218 ml/m² per day atm at 23°C temperature and at 0% relative humidity and 5235 ml/m² per day atm at 98% relative humidity.

3. Use according to claim 1, wherein the selective permeability (β= PC02/P02) is 15 at 23°C temperature and 0% humidity and is 17 at 98% humidity.

4. Use according to claim 1, wherein the humidity absorption at 25°C temperature and 98% relative humidity is 20%.

5. Use according to claim 1, wherein said usage changes the temperature-dependent permeability of the film at room temperature, 2,8 times by an increase of 10°C between the ranges of 0-40°.