Package making – With contents treating – Vacuum or inert atmosphere
Reexamination Certificate
1998-03-10
2001-02-20
Johnson, Linda (Department: 3721)
Package making
With contents treating
Vacuum or inert atmosphere
C053S089000, C141S066000
Reexamination Certificate
active
06189299
ABSTRACT:
This invention provides methods and apparatus for storing and for shipping whole or partially processed bulk fresh products under modified atmosphere that can extend the shelf life of the produce.
This invention provides methods and apparatus for gas flushing containers of fresh produce to form reduced oxygen environments in such containers without bruising the produce.
These methods and apparatus simultaneously evacuate air around and inside produce containers, minimizing pressure differentials which could cause crushing or bruising of the produce.
This invention is particularly directed to the prevention of bruising the produce while inhibiting enzymatic reactions resulting in oxidative browning and product breakdown.
This invention also provides means for obtaining specifically selected absolute pressures inside a vacuum chamber which establishes desired ratios of oxygen to inert gas inside one or more containers inside such a chamber.
The fresh produce industry continues to experience rapid growth in the production and distribution of packaged salads. The consumer is given the convenience of a fresh tasting salad, washed and ready to serve. Fresh produce is often packaged in flexible plastic bags that are designed to contain an oxygen reduced environment to prevent oxidation discoloration. More frequently, chopped, sliced or shredded produce, for example lettuce, is packaged in bags containing 10 pounds or less of product. Such fresh produce is first placed in a semi-permeable polyethylene or similar bag, and all or a portion of the air in the filled bag is withdrawn by squeezing or suctioning the bag.
Some packaging methods introduce an inert gas to replace air so removed. As air is removed from these bags, the cut pieces of produce are squeezed closely together, eliminating most of the voids where air would otherwise remain. These methods provide unacceptable results when the produce weight in the bag exceeds fifty pounds or more because of the resulting crushing and bruising of produce.
Atmospheric pressure at sea level exerts a force of approximately 14.7 pounds per square inch. To remove an adequate amount of ambient air from a large bag containing in excess of 100 pounds of fresh produce, the pressure inside the bag is often lowered to less than 3.7 pounds per square inch. The resulting differential pressure could equal or exceed 11 pounds of force on each square inch of bag surface area. For example, a whole lettuce head or like produce in contact with 16 square inches of bag surface receives a force equal to or greater than 176 pounds. This head is pressed against others inside the bag, transferring the forces to them, and causing additional crushing and bruising of the leaves and rib structure in the produce.
When a fresh produce container is rigid with airtight seals, our unique gas flushing methods and apparatus are particularly advantageous. When drawing a vacuum on such containers, the forces exerted by atmospheric pressure outside such containers can cause damage. For example, a rigid, airtight container shaped as a four foot cube experiences over 25,000 lbs of force on each side when the differential air pressure reaches 11 pounds per square inch, for a combined force of over 150,000 lbs. The construction requirements for such a container are too costly, and its empty weight too impractical for commercial use. By gas flushing such containers inside a vacuum chamber, the differential pressures are eliminated, simplifying the construction requirements for such containers.
Fresh produce has good shelf life if field heat is removed and the produce is held at a reduced temperature e.g., 33-38° F., but above freezing. Heads of lettuce deteriorate more rapidly in an oxygen-rich than in an oxygen-lean atmosphere. It is therefore desirable to store and transport cold lettuce in an environment low in oxygen concentration. When lettuce heads are partially processed in the field, either by removing the core and waste leaves, or by cutting a head into leaf pieces, the enzymatic reactions which cause deterioration accelerate. An uncut, intact lettuce head displays acceptable shelf life in environments with oxygen concentration above 5% by volume. A partially processed or fully processed lettuce head displays oxidative discoloration in a gaseous atmosphere containing above 5% oxygen by volume. Our methods can lower the oxygen concentration inside containers of lettuce heads to less than 4.0% by volume and above 0.5% oxygen without crushing or bruising the produce.
A fresh produce processor harvests and transports produce to a processing facility for chopping and slicing. In addition to transporting that portion of the fresh produce used in the salad, the processor is also hauling waste leaves, stems, cores, etc. Any damage to the fresh produce from harvesting, packing into bulk containers, or transporting to a processing facility may also result in discolored leaves from oxidation at damaged points. These leaves are also discarded as waste. Total waste may exceed 25% of the total weight in head lettuce and 40% of the total weight in romaine lettuce. The ability to ship bulk bins of produce to a processor with reduced waste offers substantial cost savings.
Our methods and apparatus improve reproducibility, and consistently form gaseous environments of desired oxygen concentration in containers for 50 pounds, 100 pounds or more of lettuce heads, other bulk leafy green produce, and other fruits and vegetables, while minimizing crushing and bruising.
Our methods and apparatus also speed produce packaging through batch processing of multiple containers, or large single containers.
Our methods of gas flushing take place inside vacuum chambers. One or more containers, e.g. bags of fresh produce are placed inside the chamber. A manifold including a tube with a hinged lid or butterfly valve on the top end, and a gas flush line attached to the side, is placed at the opening of each container. The opening atop the produce filled container, preferably a bag, is drawn tightly around the tube and affixed with a rubber band, string tie, elastic strap, ring clamp or similar device to seal the opening around the tube. Air is withdrawn from each bag and from the vacuum chamber by a vacuum pump. Air withdrawn from a container of produce flows through the tube, past an open, hinged lid, or open butterfly valve, and into the chamber for evacuation. Little difference in pressure exists between the inside and outside of the liner bag, minimizing crushing or bruising of produce in each bag during the vacuum cycle.
When the pressure inside the bag is at a desired, low level, corresponding for example to a desired, reduced oxygen concentration in the bag, the vacuum pump is stopped. Gravity, a solenoid actuator or an electric motor closes, and holds the lid closed on the top of each tube. Inert gas, e.g., nitrogen gas, is then introduced into each bag through a gas flush hose at a rate approximating the rate at which air is introduced into the vacuum chamber through a valve outside the produce bag. The produce bag is filled with a desired replacement gas until the pressure inside and outside the bag, but inside the vacuum chamber, is at or near the pressure outside the chamber. The chamber is then opened, the liner bag(s) is sealed below the tube with a tie wrap, wire tie, elastic band, heat seal, hermetic seal, or an equivalent closure, and the tube is removed.
Fresh produce, such as leafy vegetables, is vacuum cooled before storage and transport. Our methods can be combined with such cooling processes in which leafy vegetables like lettuce reach a desired temperature with both air and water vapor escaping a produce bag through a manifold tube. Such vacuum cooling may reduce the air pressure inside the vacuum chamber to a level of 4.5 to 5.0 mm Hg absolute. The chamber is then vented slightly to raise the pressure above 10 mm Hg absolute, or whatever absolute pressure value is necessary for the desired final oxygen level in the produce bag. Our methods can then follow. Alternatively, by performin
Brown Michael V.
Brown Richard S.
Bright Patrick F.
Fresh Express, INC
Johnson Linda
LandOfFree
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