US 3311287 A
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Description (OCR text may contain errors)
March 28, 1967 N ET'AL 3,311,287
FLEXIBLE CONTAINER FOR MICROWAVE STERILIZATION OF FOODSTUFFS THEREIN Original Filed Aug. 30, 1965 INVENTORS FLCRBEN E. Lona, F220 BSHAuo HARVEY c. L\ SkE ORNEYS United States Patent 4 Claims. (Cl. 229-53) This is a division of Us. application Ser. No. 305,750, filed on Aug. 30, 1963, now Patent No. 3,261,140.
This invention generally deals with the sterilization of materials in flexible pouches by means of electromagnetic energy in the microwave range. More specifically, the invention relates to light, flexible plastic pouches for mois- Lure-containing food products which are not distorted or damaged during the simultaneous sterilization and vacuumizing of the food products by means of electromagnetic energy in the microwave range.
At the present time, vacuumizing and sterilization packaging in flexible containers is accomplished primarily by one or the other of two basic methods. In the first of these methods, the product is placed in an open-mouth flexible container or pouch after which the container and the mouth thereof mechanically grip and close about an inserted hollow probe or snorkle. The hollow probe or snorkle is attached to a pumping system which evacuates the gases, including air, from the container. A heat seal is then applied to the mouth of the container as the probe is withdrawn in such a manner and with such timing as not to allow leakage of air back into the container. The sealed, filled container is then essentially free of any gaseous content and, commercially, the interior of the container is considered to be a vacuum where not occupied by solid, liquid or both.
In the other packaging method, open-mouth flexible containers are first filled and then with their mouths unsealed, one or more filled containers is placed in a receptacle. The receptacle is then sealed and evacuated by mechanical means. When the total volume of the receptacle has been reduced to a commercial vacuum, the evacuated containers are then sealed by a sealing device contained within the evacuated receptacle, but remotely controlled. After all of the containers have been sealed, the vacuum in the-receptacle is then broken and the sealed, filled containers are removed.
In either of the above outlined methods, itis'possible but quite difficult to either pasteurize or sterilize the contents of the containers during the vacuumizing, and this is generally accomplished by a heating or irradiation process performed after complete vacuumizing.
In accordance with a more recent method of packaging food products, a pliable heat-scalable plastic container having an open end is filled with a product together with such liquid as required to fill the container with vapor when heated. A portion of the container is then heatsealed to form a vent passage through which vapor is purged when the container is heated. Upon subsequent cooling of the container, the vapor condenses and the vent passage is temporarily sealed. Thereafter, the container is further heat-sealed to completely close the vent passage. In accordance with this method, simultaneous sterilization and vacuumizing is achieved with relative case. However, several disadvantages in the practice of'this method have been noted, prominent among which is the difliculty of killing bacteria in upper corners of the containers adjacent the vent passage. The corners of the con tainers define abrupt pockets which are extremely difficult to sterilize because the vapor tends to by-pass the corners 3,311,287 Patented Mar. 28, 1967 to a major extent as it passes from the head space of the containers outwardly thereof through the vent passage.
It is, therefore, a primary object of this invention to provide a novel flexible container for use in vacuum and sterilization packaging which overcomes the above-noted and other disadvantages, the container having a partial seal defining a vent passage, the vent passage being tortuous to permit vapor to escape from the container under pressure, and the container including at least one corner adjacent the vent passage which is concavely contoured between the vent passage and an adjacent side of the container, thereby eliminating conventional abrupt corner configurations and lessening the chance of any bacteria that is viable in a food product remaining alive after the container has been heated.
With the above and other objects in view, as will hereinafter appear, the nature of the invention will be more clearly understood by reference to the following detailed description and the accompanying drawing.
In the drawing:
FIGURE 1 is a perspective view of an apparatus for sterilizing and vacuumizing a product-containing container of this invention.
FIGURE 2 is a front view of a partially sealed, flexible plastic container having a product contained therein with parts of the container having been broken away and shown in section.
FIGURE 3 is a partial sectional end view taken along the line 3-3 of FIGURE 1, and shows in particular the construction of the plastic container holder and the manner in which it operates so as to prevent distortion of the container during vapor emanation.
The product materials which have utility in the present invention include chemicals, pharmaceuticals and food materials having relatively high dielectric constants. The product to be sterilized and vacuum-packaged may be in either liquid or solid form. The invention has particular utility concerning high acid foodstuffs, such as fruits, and vegetables, and includes such specific items as strawberries, raspberries, apples, tomatoes and pickled beets. The invention is, however, not limited to foodstuffs.
An important feature in carrying out the invention is that the dielectric constant of the product must be high in relationship to the container-forming material. The container may be formed of any suitable polymeric material film which has a relatively low dielectric constant and preferably embraces those polymeric materials which are of a relatively symmetrical nature. Specific examples of suitable polymeric films are those of the hydrocarbon and polyester groups, such as polyethylene, both high and low density, polypropylene and polyethylene terephthalate Mylar.
Referring to the drawing, a suitable system 5, as shown in FIGURE 1, is utilized to carry out the present proc ess. A microwave oven 6, such as disclosed in U.S. Patent No. 2,467,230, is suitably disposed along the system 5 so as to receive flexible containers or pouches 7 (FIG- URE 2) partially filled with a product 8. The oven 6 is adapted to heat and sterilize the product 8 while only negligibly heating the roduct-containing container 7. The microwave oven 6 is preferably arranged to operate in the 1 mm. to 30 cm. wave length range, with corresponding frequencies from 300,000 to 1,000 megacycles.
A conveyor belt 9, mounted on rollers 10, is arranged to transport the filled pouches 7 into and out of the microwave oven 6. The rollers 10 are mounted upon shafts 11, one of which is driven by suitable means (not shown). The belt 9 is preferably constructed of a low dielectric material and may consist of the same material utilized in the construction of the containers or pouches 7. Open top container holders 12, each having a base 13 and relatively high side walls 14, are secured along the belt 9 at a equally spaced intervals. The holders 12 are also made of low dielectric constant material and are fastened through the bases 13 thereof to the belt 9'by suitable means, such as plastic rivets 15, also of low dielectric constant material. The holders 12 are further shaped so as to conform to the outer configuration of the filled plastic pouches 7.
A pouch dispenser 16 is mounted directly above the belt 9 at one end thereof and dispenses a pouch 7 into a holder 12 in timed relationship to the movement of the belt 9. The pouch 7 is preferably formed with a seamless tubular wall 17 which is heat-sealed at its bottom 18 prior to its insertion into the holder 12. The exact configuration and construction details of the pouch may, however, be varied. As belt 9, the holder 12, and the pouch 7 move away from the pouch dispenser 16, the upper most walls of the pouch extend upwardly beyond the side walls 14 of the holder 12 and are open for receipt of the product 8 within the interior of the pouch 7. 'A product dispenser 19 is located above the belt 9 in its associated holders 12 and is adapted to dispense the product 8 into the interior of the pouches 7 in timed relation to the movement of the belt 9. The product 8 must contain moisture and is dispensed into the pouches 7 to a level 20 belowthe termination of the side walls 14 of the plastic holder 12 so as to provide a head space 21 within the plastic pouch 7 above the level 20 of the product 8 contained therewithin.
A heat sealing station 22 is disposed above the belt and downstream of the product dispenser 19. Included in the heat sealing station 22 are parallel bars 23 which have outwardly flared end portions 24 which operate to gather and align the top portions of walls 17 into parallel and opposed relationship. The parallel bars 23 are each connected to a spring 25 for urging the bars 23 together. The parallel aligned portions of the wall 17 are then fed between opposed heated rollers 26, 27 which heat-seal portions of the tubular wall 17 together. The heated sealing rolls 26 and 27 are mounted for rotation on suitable shafts 28 and their surfaces are so configured so as to heat-seal only portions of the wall 17 so as to fashion one or more vents or passages which communicate between the interior of the pouch 7 and atmosphere. Those portions of the wall 17 which are heat-sealed are designated 29, while the unheat-sealed portions form the vents 30 which normally are of a tortuous configuration (FIG- URE 2). Also, the sealing rolls which form the heat seal 29 are contoured to form gradually curved, heatsealed corner portions 47 between side edgesv 41 and the respective vents 30. These corner portions permit hot steam escaping through the vents 30 to sterilize the entire interior of the head space 21 and assures that no interior portion of the pouch is not fully exposed to hot sterilizing steam, as will be more clearly apparent hereafter.
The thus partially sealed pouch 7 having the product 8 contained therein is then advanced by the movement of the belt 9 into the microwave oven 6 with the pouch 7 and the product 8 being subjected to the action of the electromagnetic wave impulses in the microwave range. As the belt 9, the holder 12, and the pouch 7 are made up of relatively low dielectric constant materials and since the product 8 has a dielectric constant which is relatively high in comparison to its surrounding materials, the microwave energy will be primarily dissipated in heating the product 8. The product is thus heated to approximately 100 C. with only slight accompanying heating of the pouch 7, the plastic holder 12 and the belt 9. It is thus apparent that by using the disclosed method, apparatus and container, the product 8 can be sterilized without resorting to prior art methods which utilize the container walls as a conductive element through which the sterilization heat is applied to the product.
The rise in the temperature level is not only useful in the sterilization of the product 8. but further serves to expand the air within the head space 21 and to volatilize the moisture contained within the product 8 into steam. Normally, the production of large quantities of steam would cause a ballooning of the portions of the Walls 17 and surround head space 21 if it were not for the high side walls 14 of the plastic holder 12. The high side walls 14 thus serve to maintain the pouch 7 in its normal configuration and prevent excessive ballooning during the very rapid steam generation. By preventing ballooning of the tubular plastic walls 17, the plastic holder 12 thus increases the rate at which the steam and air may be evolved through the tortuous vents 30.
The pouch 7 containing the sterilized product 8 is, immediately following its withdrawal from the microwave oven, entirely sealed across the top portions of the walls 17 so as to close off and seal the vents 30. A heat-sealing station 31 similar to the station 22 is associated in proper relationship to the belt 9 for this purpose, the essential difference being that the rollers 32 and 33 are instead of being designed to only partially seal the top portions of the wall 17, are adapted to entirely seal portions of the wall 17 including the vents 30.
The cooling of the product 8 after its withdrawal from the microwave oven causes a partial vacuum within the pouch 7 of the condensation of the steam within the head space 21. The pouch 7 and the sterilized and vacuumized product 8 are then transferred to a second conveyor belt 34 for packing, storage and shipment. A pouch or bag guide 35 having an open bottom (unnumbered) is positioned slightly above the conveyor belt 34 by a suitable support member 36. As each pouch 7 is transferred from the holder 12 to the conveyor belt 34, the guide 35 positions each pouch upside down upon the conveyor belt and prevents the pouch from falling over upon its side during the transfer In this upside-down position, the heat-seal portion 29 easily collapses and lies flat on the conveyor 34 and the hot product 8 completely fills the head space 21.
The reason for transferring the pouches onto the conveyor belt 34 in an inverted or upside-down position is to kill any remaining bacteria that is viable in the pouches.
Thus, it is apparent that there has been provided a simple pouch and associated method and apparatus for simultaneously sterilizing and vacuumizing a product which is contained within a flexible plastic pouch capable of "being heat-sealed. p
Specific examples of the herein-described invention are as follows:
Example I Stewed tomatoes from the same run as utilized in Example I were packaged and treated in the same manner as in Example I except that two 800-watt microwave genera-tors (Raytheon Industrial Unit) were utilized instead of the one 900-watt generator. The product-containing pouches were treated for 1 /2 to 2% minutes. The test resulted in commercially sterile products.
Example 111 Whole ripe raspberries were treated in the manner set forth in Example II. The comparative test also resulted in a commercially sterile product.
It is obvious that the specific examples are not restrictive, and that the invention may be practiced in other ways within the scope of the appended claims.
1. A pouch particularly adapted for formation into a package for products which are sterilized by steam generated in the pouch and vented to atmosphere through a passage which is subsequently hermetically sealed comprising a generally tubular body Wall having a closed end portion and an oppositely heat-sealed end portion, said heat-sealed end portion being defined in .part by a free edge and adjacent side edges, said heat-sealed end-portion having at least a single unsealed tortuous portion forming a passage from an interior chamber of said pouch to the exterior thereof, said tortuous portion including heat sealable means for subsequently closing said passage under the application of heat and pressure thereto, said chamber being defined in part by said heat-sealed end portion, and an edge portion of said heat-sealed end portion extending angularly from said passage to one of said side edges whereby steam generated in said chamber is gradually guided toward the passage by said edge portion and any bacteria therealong are destroyed by the steam.
2. The pouch as defined in claim 1 wherein said edge portion opens concavely toward the chamber to defiine a 6 curved interior corner portion of said chamber between said passage and said one side edge.
'3. The pouch as defined in claim 1 wherein said heat sealed end portion includes a second unsealed tortuous portion fiormin-g another passage from the chamber of said pouch to the exterior thereof, said heat-sealed end portion includes another edge portion, and said another edge portion extends angularly from said another passage to the other of said side edges.
4. The pouch as defined in claim 3 wherein each of said edge portions opens concavely toward the chamber to define a curved interior corner portion of the chamber between each passage and an adjacent associated one of said side edges.
References Cited by the Examiner UNITED STATES PATENTS 2,361,344 10/1944 Yates. 3,133,691 5/1964 Corbett 22953 3,186,625 6/1965 Mead et a1. 229-53 JOSEPH R. LECLAIR, Primary Examiner. DAVID M. BOCKENEK, Examiner.