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Packaged stabilized foodstuff

Packaged stabilized foodstuff description/claims

The present invention relates to methods for the manufacture of packaged stabilised foodstuffs, and to the stabilised foodstuffs obtainable thereby.

Conventional food sterilisation techniques rely on heating the foodstuff in a pressurised chamber (retort) at temperatures of from about 110° C. to about 130° C. for periods of from about 30 minutes to about 1 minute. Unfortunately, these methods cannot be used with containers comprising flexible films bonded by a peelable seal, that is to say a seal that can be pulled apart without rupturing the sheet material from which the package is made. Preferably, the peelably seal can be peeled apart by a force as hereinafter defined of 20N or less, which enables the package to be opened easily using only finger strength. However, it has been found that the temperature and pressure changes during the sterilisation cycle rupture or weaken peelable seals to an unacceptable degree. Therefore, conventional autoclave sterilisation requires the use of packages that have stronger seals that typically cannot be separated without tearing the material from which the package is made. Such packages usually require utensils such as scissors to open them, and can present difficulties for disabled or elderly persons.

WO97/21361 describes the preparation of stabilised foodstuffs by application of Ultra high pressure (UHP) in the range 300 MPa to 1000 MPa to foodstuffs having a pH greater than about 4.5, wherein the foodstuffs have been preheated to temperatures of at least about 75° C. The additional adiabatic heating due to the UHP raises the temperature of the foodstuffs to a temperature sufficient to achieve inactivation of bacterial spores and shelf stability.

It has now been found that UHP can be applied, even at elevated temperatures, to packages having easy-to-open, peelable seals without rupturing or weakening the seals.

In a first aspect, the present invention provides a method of packaging and stabilising a foodstuff comprising the steps of: forming a package comprising a peelable seal in at least a region of the package and filling the package with the foodstuff; followed by treating the package at ultra high pressure (UHP) to stabilise the foodstuff in the package without rupturing the peelable seal.

The package may consist essentially of the sealable sheet material. The package may for example be a sachet or pouch. Suitably, the step of forming the package comprises forming a flexible pouch substantially from said sealable sheet material. For example, the step of forming the package may comprise bonding two sealable sheets in face to face relationship to provide a flexible pouch, or the process may comprise folding-over a single sealable sheet, and bonding the margins of the sheet together to form edges of the flexible pouch.

The filling of the package with the foodstuff takes place after initial forming of the package, but before final sealing of the package.

For example, one common packaging technique is form-fill-seal packaging, including vertical form-fill-seal (VFFS) packaging. In VFFS packaging, a flat web of flexible, sealable film is unwound from a roll and formed into a continuous tube in a tube-forming section, by sealing the longitudinal edges on the film together to form a so-called lap seal or a so-called fin seal. The tube thus formed is pulled vertically downwards to a filling station. The tube is then collapsed across a transverse cross-section of the tube, the position of such cross-section being at a sealing device below the filling station. A transverse seal is made, by the sealing device, at the collapsed portion of the tube, thus making an air-tight seal across the tube. The material being packaged enters the tube above the transverse heat seal in a continuous or intermittent manner, thereby filling the tube upwardly from the transverse seal. The tube is then allowed to drop a predetermined distance usually under the influence of the weight of the material in the tube. The jaws of the sealing device are closed again, thus collapsing the tube at a second transverse section, which may be at, above or below the air/material interface in the tube, depending on the nature of the material being packaged and the mode of operation of the process. The sealing device seals and severs the tube transversely at the second transverse section. The material-filled portion of the tube is now in the form of a pillow shaped pouch. Thus, the sealing device has sealed the top of the filled pouch, sealed the bottom of the next-to-formed pouch and separated the filled pouch from the next-to-be formed pouch, all in one operation.

Variations on pouch-forming machines and in particular on this type of vertical form fill and seal apparatus are either known or conceivable. For example, the forming and sealing functions may be performed separately from severing function on separate machines. Also, the jaws of the sealing device could move to the next sealing position rather than have the film drop to the next position or there could be two sets of sealing jaws that seal both transverse ends simultaneously. Further, instead of forming a tube, two pieces of film could be fed into the machine and the pouch could be made by four seals, two longitudinal and two transverse. It will also be appreciated that form-fill-seal equipment can be operated in non-vertical mode, for example in horizontal mode, especially for packaging unitary items.

The transverse seals at the top and/or the bottom of each pouch may be the peelable seal. Suitably, the longitudinal seal (where present) has a higher peel strength and may be substantially non-peelable, that is to say the sheet material will tear before the seal will separate.

In addition to the form-fill-seal equipment described above, the method according to the present invention may comprise filling and sealing stand-up pouches. That is to say, pouches formed from flexible, sealable film having front and back panels and a bottom panel forming a gusset to allow the pouch to stand up after filling. The pouches are individually filled, and then sealed along the top edges of the front and back panels. Suitably, the seal along the top edge is a peelable seal, and the other seals are substantially non-peelable, that is to say they have a substantially greater opening force.

Generally, in the methods and packages of the invention, the bonding may be weaker in a first region of the sheet material than in other bonded regions of the sheet material, whereby the peelable seal is formed in the first region.

In certain embodiments, the step of forming the package comprises providing a formed tray or pot and sealing the sealable film across the top of the tray. The formed tray is suitably produced by thermoforming a sheet of relatively rigid (compared to the sealable sheet) thermoplastic sheet material. The formed tray typically comprises a recess for storage of the food product, and a flange around the top of the recess for attachment of the heat sealable sheet material.

Suitably, the seal strength of the peelable seal as measured by ASTM F88-00 is in the range of from about 2N to about 30N, preferably from 5N to about 20N, both before and after the UHP treatment. This seal strength range provides mechanical robustness and leak resistance to the package, while allowing easy opening of the package by peeling. In principle, the sealstrength should be as low as possible consistent with maintaining product integrity.

In principle, any of the many sealable sheet materials may be used in the practice of the present invention. Suitably, the sealable sheet material is a heat-sealable sheet material. Typically, the sealable sheet is a film laminate comprising a core layer and a sealing layer.

Suitably the sealing layer consists primarily of a polyethylene or a polypropylene. That is to say, preferably at least 50% by weight of the sealing layer is made up of a polyethylene or a polypropylene. Especially suitable polyethylenes are linear low-density polyethylenes (LLDPE) and ultralow density polyethylenes (ULDPE) made by copolymerising ethylene and C3-C8 alpha-olefins. Polymers of this type are described for example in EP-A-0351189.

The sealing temperature of the heat sealing layer should be selected to provide the desired peel strength. The heat sealing temperature is defined herein as the temperature at which the sealing step is carried out. The polymers of the sealing layer can be selected in conventional fashion to have a heat sealing temperature in the desired range. In conventional heat-sealing embodiments, the heat sealing temperature is typically from about 120° C. to about 160° C., for example from about 130° C. up to about 150° C. In other embodiments, a cold-sealing film may be used, that is to say a film having a sealing temperature of less than 100° C., typically less than about 50° C., for example about ambient (20° C.). The latter films are sealed simply by applying pressure at a temperature within the cold sealing temperature range. It is a surprising feature of the present invention that seal integrity can be maintained during the UHP treatment step even if the peak temperature reached during UHP treatment exceeds the sealing temperature at which the peelable seal was formed.

The base layers to be combined with the sealing layer in the multilayer structures for use in the present invention can be selected from among suitable film-forming polymers, regenerated cellulose, paper, paperboard, fabric and aluminium foil. The film-forming polymers include polyamide resins, e.g., nylon 6, nylon 66, nylon 11, and nylon 12; polyester resins, e.g., polyethylene terephthalate (PETP) and polybutylene terephthalate; polyolefin resins, e.g., polypropylene (PP), oriented polypropylene (OPP), poly-1-butene, poly-4 methyl-1-pentene, polyethylene, an ethylene-vinyl acetate copolymer, an ethylene-methacrylate copolymer, an ethylene-acrylate copolymer, an ethylene-methacrylic acid copolymer, and ionomers; polyvinylidene chloride; polyvinyl chloride; polystyrene; polyvinyl alcohol (EVOH); or an ethylene-vinyl alcohol copolymer. These film-forming polymers can be chosen according to the end use of a composite film taking into consideration gas barrier properties, printability, transparency, rigidity, adhesion, or the like factor. In cases of using stretchable bases, particularly those which are stretched to provide improved film characteristics, such as polyamide resins, polyester resins and polypropylene, the base may be uniaxially or biaxially stretched, if desired. Multilayer base structures are also possible.

In the sealable composite films, the sealing layer usually has a thickness of from 1 to 500 micrometers, preferably from 10 to 200 micrometers, more preferably from about 50 to about 100 micrometers. The thickness of the base layer is arbitrary and can be decided depending on the packaging application.

The composite sealing films composed of two or more layers can be produced by known processes, such as: lamination processes including dry lamination, wet lamination, sandwich lamination, and hot-melt lamination; co-extrusion such as blown film extrusion or T-die extrusion; extrusion coating (called extrusion lamination); and combinations thereof.

Suitably, the UHP processing is carried out at a pressure of from about 250 MPa to about 200 MPa, more suitably from about 400MPa to about 1200 MPa, for example from about 500 MPa to about 1000 MPA. Suitably, the total treatment time is from about 1 minute to about 30 minutes, for example from about 2 minutes to about 20 minutes. The UHP is preferably hydrostatic pressure, i.e. applied in batch fashion. The UHP may be applied in intermittent or pulsed fashion, for example as described in EP-A-1112008, the entire contents of which are incorporated herein by reference. In that case the treatment time herein is the total time spent at or above 150 MPa.

The starting temperature for the UHP treatment may be ambient temperature (15-30° C.), or the package may be preheated before application of UHP. In certain embodiments, the package is preheated to a temperature of at least about 70° C., for example at least about 80° C. or 90° C. before pressurisation.

The above temperature ranges refer to the temperature of the sauce in the uncompressed state; adiabatic heating may raise the temperature of the sauce by more than 5° C., for example by at least 10° C., typically about 10-20° C. during compression. Preferably, the pressurization is carried out under substantially adiabatic conditions. Suitably, the package is instantaneously heated by the UHP adiabatic compression to a peak temperature of at least about 110° C.

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