Electric heating – Metal heating – By arc
Reexamination Certificate
2002-06-26
2004-05-04
Heinrich, Samuel M. (Department: 1725)
Electric heating
Metal heating
By arc
Reexamination Certificate
active
06730874
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to the field of packaging for respiring or biochemically active agricultural products and commodities such as fresh fruits, fresh vegetables, fresh herbs, and flowers (herein referred to collectively as produce or fresh produce) and more particularly to registered microperforations in packaging materials for use in modifying or controlling the flow of oxygen and carbon dioxide into and/out of a fresh produce container.
BACKGROUND OF THE INVENTION
The quality and shelf life of many food products is enhanced by enclosing them in packaging that modifies or controls the atmosphere surrounding the product. Increased quality and longer shelf life result in fresher products for the consumer, less waste from spoiled produce, better inventory control, and appreciable overall savings for the food industry at both the retail and wholesale levels.
Modified atmosphere packaging (MAP) and controlled atmosphere packaging (CAP) are often used interchangeably in the industry, and much confusion exists on their exact meanings. Both refer to methods to control the atmosphere in the package. In the processed foods area, MAP is considered a static method for controlling the atmosphere whereby an initial charge of a specific gas composition, e.g. 30% CO
2
and 70% N
2
, is introduced into a barrier container before sealing.
The oxygen transmission rate (OTR) of a film is expressed as cc O
2
/m
2
-day-atmosphere, where one atmosphere is 101325 kg/ms
2
. Generally, a barrier container is one that has an OTR of <70 cc/m
2
-day-atm. The units describing the flow of a particular gas through a film are “flux”, expressed as cc/day-atm.
For fresh produce, the primary means to extend quality and shelf life is temperature control. However, more than 50 years of evidence from industry practices on bulk storage of fresh fruits and vegetables in refrigerated controlled atmosphere storage rooms has shown that atmosphere control can contribute greatly to quality retention and shelf life. The use of MAP/CAP for fresh produce was a natural progression once packaging technology had advanced to include the production of non-barrier (often referred to in the industry as “breathable”) materials.
The goal in fresh fruit and vegetable packaging is to use MAP/CAP to preserve produce quality by reducing the aerobic respiration rate but avoiding anaerobic processes that lead to adverse changes in texture, flavor, and aroma, as well as an increased public health concern. Aerobic respiration can be defined by the following equation:
(CH
2
O)n+nO
2
→nCO
2
+nH
2
O+heat
where O
2
from the air is used to metabolize carbohydrate ((CH
2
O)n) reserves and in the process, CO
2
, and H
2
O are produced and heat is generated. For each respiring item, there is an optimum O
2
and CO
2
level that will reduce its respiration rate and thereby, slow aging and degradative processes. Different fresh produce items have different respiration rates and different optimum atmospheres for extending quality and shelf life.
The concept of passive MAP became common with the development of packaging materials with OTRs of 1085 to 7000 cc/m
2
-day-atm for fresh-cut salads. In passive MAP, the produce is sealed in packages made from these low barrier materials and allowed to establish its own atmosphere over time through produce respiration processes. Sometimes the package is gas-flushed with N
2
or a combination of CO
2
and N
2
, or O
2
, CO
2
, and N
2
before sealing to rapidly establish the desired gas composition inside the package. Alternately, a portion of the air may be removed from the pack, either by deflation or evacuation, before the package is sealed, to facilitate rapid establishment of the desired gas content.
In CAP, the atmosphere in the package is controlled at well-defined levels throughout storage. CAP can take many forms, and may even involve enclosing gas absorber packets inside processed food barrier packages. For example, CO
2
absorber sachets may be sealed inside coffee containers to absorb and control the level of CO
2
that continues to be generated by the ground coffee. Sachets containing iron oxides are enclosed in barrier packages of fresh refrigerated pasta to absorb low levels of O
2
entering the package through the plastic material.
CAP of fresh produce is just a more controlled version of MAP. It involves a precise matching of packaging material gas transmission rates with the respiration rates of the produce. For example, many fresh-cut salad packages use passive MAP as described herein. If the packages are temperature-abused (stored at 6-10° C. or higher), O
2
levels diminish to less than 1%, and CO
2
levels can exceed 20%. If these temperature-abused packages are then placed back into recommended 3-4° C. storage, the packaging material gas transmission rates may not be high enough to establish an aerobic atmosphere (<20% CO
2
, >1-2% O
2
) so fermentation reactions cause off-odors, off-flavors, and slimy product. If the salad was in a CAP package, the O
2
levels would decrease and CO
2
levels increase with temperature abuse, but would be re-established to desired levels within a short time after the product is returned to 4° C. storage temperatures.
Today, films made from polymer blends, coextrusions, and laminate materials with OTRs of 1085 to 14,000 cc/100 m
2
-day-atm are being used for packaging various weights of low respiring produce items like lettuce and cabbage. These OTRs, however, are much too low to preserve the fresh quality of high respiring produce like broccoli, mushrooms, and asparagus. In addition, existing packaging material OTRs for bulk quantities (>1 kg) of some low respiring produce are not high enough to prevent sensory quality changes during storage. Therefore, several approaches have been patented describing methods to produce packaging materials to accommodate the higher respiration rate requirements and higher weights of a wide variety of fresh produce items.
U.S. Pat. Nos. 4,842,875, 4,923,703, 4,910,032, 4,879,078, and 4,923,650 describe the use of a breathable microporous patch placed over an opening in an essentially impermeable fresh produce container to control the flow of oxygen and carbon dioxide into and out of the container during storage. Although this method works effectively, the breathable patch must be produced by normal plastic extrusion and orientation processes, whereby, a highly filled, molten plastic is extruded onto a chill roll and oriented in the machine direction using a series of rolls that decrease the thickness of the web. During orientation, micropores are created in the film at the site of the filler particles. Next, the microporous film must be converted into pressure sensitive adhesive patches or heat-seal coated patches using narrow web printing presses that apply a pattern of adhesive over the microporous web and die-cut the film into individual patches on a roll. These processes make the cost of each patch too expensive for the wide spread use of this technology in the marketplace. In addition, the food packer has to apply the adhesive-coated breathable patch over a hole made in the primary packaging material (bag or lidding film) during the food packaging operation. To do this, the packer must purchase hole-punching and label application equipment to install on each packaging equipment line. These extra steps not only increase packaging equipment costs, but also greatly reduce packaging speeds, increase packaging material waste, and therefore, increase total packaging costs.
An alternative to microporous patches for MAP/CAP of fresh fruits and vegetables is to microperforate polymeric packaging materials. Various methods can be used to microperforate packaging materials: cold or hot needle mechanical punches, electric spark and lasers. Mechanical punches are slow and often produce numerous large perforations (1 mm or larger) throughout the surface area of the packaging material, making it unlikely that the atmosphere inside the package will be modified
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