Refrigeration – Processes – Treating an article
Reexamination Certificate
2002-08-02
2003-11-11
Doerrler, William C. (Department: 3744)
Refrigeration
Processes
Treating an article
C062S270000, C062S264000, C062S100000, C099S278000
Reexamination Certificate
active
06644043
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
This invention provides methods and apparatuses for applying controlled elevated temperature water to fresh produce such as lettuce, broccoli and potatoes to create a heat-shock response in the produce tissue, and then removing the water and cooling the produce by vacuum evaporation of the water, leaving the produce tissue at a desired temperature and with a desired moisture content.
U.S. Pat. No. 5,992,169, incorporated herein by reference as though fully set forth here, discloses vacuum cooling and drying of fresh produce such as lettuce, and apparatus therefor, as an alternative and superior method to centrifuge drying and cooling, or forced air drying and cooling of processed produce. Pertinent parts of the specification are included in this application. Vacuum cooling, and drying requires less handling, and, therefore, causes less abrasion and abuse of produce tissue, reducing wound response and browning of the tissue, and enhancing marketability.
Produce sprayed or immersed in water absorbs and adsorbs water. For example, iceberg lettuce immersed in water after being chopped or cut may take up to twenty percent or more of its weight in water. The more water that the lettuce tissue absorbs/adsorbs, the higher the temperature must be to evaporate unwanted water in a given time period, in the vacuum evaporation process. (See FIGS.
2
A and
2
B).
To minimize lettuce residency time in rinse water without sacrificing produce quality, research has been done to determine what the upper temperature limit of lettuce rinse water could be. Surprisingly, lettuce tissue can withstand rather high air and water temperatures. Warm air or water applied to produce tissues causes a preservation response called a heat-shock response. See Loaiza-Velarde, J. G., Thomas-Barbera, F. A., and Saltvelt, M. E., “Effect of Intensity and Duration of Heat-shock Treatments on Wound-induced Phenolic Metabolism in Iceberg Lettuce,” J. Amer. Soc. Hort. Sci. 122(6):873-877 (1997), incorporated by reference as though fully set forth herein. This response causes physiological changes in produce tissue which, when growing, aids in survival, and, after harvest, preserves marketability. This response causes enzyme changes in lettuce, especially processed lettuce, which can delay or prevent discoloration, e.g. browning, increasing lettuce marketability. (By “processed lettuce” is meant lettuce that has been cut, chopped, shredded and/or cored.) In accordance with the present invention, this ability of produce to withstand elevated water temperatures and, in fact, to benefit from this immersion, also provides a synergistic relationship with the vacuum cooling and drying of fresh produce, in that the rinse water removal by vacuum drying, i.e. evaporation, is made more effective or efficient by the elevated starting temperature of the water. In its optimum aspects, the present invention utilizes the synergistic combination of heat shock and vacuum drying and cooling. Nevertheless, the Invention contemplates the same synergism by using an elevated temperature rinse water, which may be above the starting temperature of the produce, even though that elevated temperature is less than that which will produce heat shock.
At present, the packaged salad industry utilizes proper cooling, special semipermeable membrane bags, and/or modified gas atmospheres to control the metabolism of plant tissue and to minimize browning of produce, especially processed lettuce. Immersion of such produce in water at a temperature in the range of 50° F. to 160° F. for a suitable time to produce the heat-shock response, itself inhibits browning.
For additional information, see the following publications:
1. Brecht, J. K., 1995, “Physiology of Lightly Processed Fruits and Vegetables,” Hort Science 30: 18-22.
2. Bolin, H. R. and Hursoll, C. C., 1991. “Effect of Preparation Procedure and Storage Parameters on Quality Retention of Salad-Cut Lettuce,” J. Food Sci., 56: 60-67.
3. Couture, R., Cantwell, M. I., Ke, D, and Saltviet, N. E., 1993. “Physiological Attributes and Storage Lite of Minimally Processed Lettuce,” Hort. Science 28: 223-725.
4. Ke, D. and Saltviet, N. E., 1988, “Plant Hormone Interaction and Phenolic Metabolism in the Regulation of Russet Spotting in Iceberg Lettuce,” Plant Physical; 88; 1136-1140.
5. Loaize-Velarde, J., Tomas-Barberan, F. A., Saltviet, N. E., 1997. “Effect of Intensity and Duration of Heat Shock Treatments on Wound Induced Phenolic Metabolic in Iceberg Lettuce,” J. Amer Soc. Hort. Science 122(6): 873-877.
6. Lopez Galvez, G. Saltviet, M. E., and Cantwell, M., 1997. “Wound Induced Phenylalanine Ammonia Lyase Activity: Factors Affecting its Induction and Correlation with the Quality of Minimally Processed Lettuce,” Postharvest Biol. Technol. 9: 223-233.
7. Pollock, C. F., Eagles, C. F., Howarth, C. J., Schunumann, P. H. D., and Stoudart, J. L., 1993. “Temperature Stress”
0
p. 109-132 In: L. Fowden, T. Mansfield, J. Stoudart (Eds)
Plant Adaptation to Environmental Stress.
Chapman and Hall, New York.
8. Saltviet, M. E., 1997. “Physical and Physiological Changes in Minimally Processed Fruits and Vegetables,” p. 205-220 In: F. A. Tomes Barberan (Ed.)
Phytochemistry of Fruits and Vegetables.
Oxford University Press, Oxford, UK.
9. Vierling, E., 1991, “The Roles of Heat Shock Proteins in Plants.” Annu. Rev. Plant Physiol. Plant. Mol. Biol. 42:579-620.
Summary of the Invention
This invention provides methods for delivering produce, especially processed produce such as lettuce, broccoli and potatoes at a desired temperature and a desired moisture content, after the produce has been subjected to a heat shock or other anti-browning treatment. The process of heat-shocking produce, then cooling and drying it, can be applied to any produce In need of cooling and drying for shipment or storage, but is especially effective on lettuce, such as iceberg lettuce.
For most processed produce, and particularly for green leafy produce such as lettuce, where the harvest temperature of the produce is in the range of about 35° F. to about 90° F., the heat-shock reaction takes place and can be detected when the processed produce is exposed to a temperature about 18° F. higher than the harvest temperature of the produce. However, It Is Important not to heat the produce too much. Proper heat shock treatment therefore depends on the temperature of the produce at the outset of the heat-shock process, the temperature of the water utilized to cause the shock, and the time needed to create the heat-shock response, i.e. BTU's delivered. Preferably, but not necessarily, the produce has a temperature of about 50° F. at the beginning of the heat-shock process, but could have a temperature as low as about 33° F. The exposure to higher temperature water, e.g. water at a temperature of about 50° F. to about 160° F., continues until the heat-shock response has taken place, e.g., for about 30 to 480 seconds. Thereafter, the temperature of the produce is reduced to the range between about 34° F. and about 41° F., i.e. to a temperature where the metabolism of the produce Is slowed substantially without killing the produce.
The processing (cutting, chopping, shredding, and/or coring) of lettuce induces alterations in the phenolic metabolism of the lettuce which causes browning, reducing quality. Phenylalanine ammonia-lyase (PAL) and the concentration of phenolic compounds (e.g. chlorogenic acid, dicaffeoyl tartaric acid and iso-chlorogenic acid) increase in wound areas after processing. This increase in the wound response enzyme activity is reduced when the cut tissue is exposed to a heat-shock environment which redirects the protein synthesis away from a cut-shock response.
The reduction of PAL activity Increases with the duration of heat-shock treatment, and the reduction of PAL Increases faster as the water temperature increases. PAL activity is barely detected after a 60-second treatment with 155° F. water. However, heat-shock treatment at a water temperature above 140° F. and up to about 155°
Kleinberg & Lerner ,LLP
Later Roger Carson
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