Methods of preserving plant material

Details Methods of preserving plant material Methods of preserving plant material

1996-09-17

1997-10-14

Dudash, Diana

Stock material or miscellaneous articles

Three dimension imitation or 'treated' natural product

Flora

427 4, A01N 300

Patent

active

056770197

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to methods of preserving plant material, and in particular to methods of preserving cut green foliage and flowers for use in decorative displays.
At present there is no really satisfactory method of preserving fresh green foliage and freshly cut flowers such as are used in decorative arrangements and displays. The foliage and flowers can be preserved by drying, but this results in drastic shrinkage of flowers, colour changes and brittleness. Other methods attempt to preserve freshly cut flowers and foliage without loss of the fresh plant texture and resilience of the material. For example, it has been known for some time that freshly cut flowers and foliage can be preserved by dipping the cut stems in an aqueous solution of glycerol for a few days. The glycerol is imbibed into the plant material by transpiration and replaces some of the water normally present in the plant material. The glycerol then inhibits saprophytic degradation of the plant material and considerably extends its life. Unfortunately, this method of introducing glycerol into the plant material by making use of the natural transpiration of the plant material (sometimes called perfusion) is extremely slow, even when the conditions of temperature and high relative humidity of the ambient air are optimised. A further difficulty is that glycerol causes drastic colour changes in plant material into which it is absorbed, particularly when that plant material is exposed to light. As a result, it has been found necessary to add dyes to the glycerol solution in order to compensate for the effects of these colour changes. In practice, the use of glycerol as a preservative is restricted to plant materials such as copper beech foliage that do not exhibit a fresh green appearance in their natural state. Yet another problem with preservation of plant material using glycerol solutions is that there frequently occurs bleeding, or weeping, of glycerol solution from the surfaces of the plant material. This is especially apparent in conditions of high relative humidity. Beads of glycerol solution form on the surface of the plant material and may even drip from the plant material. Clearly, this is unsatisfactory and unsightly.
Various attempts have been made to modify or improve the preservation of plant material using glycerol. For example, U.S. Pat. No. 4,287,222 describes a method for preserving cut plant material which comprises immersing the material in pure glycerol at elevated pressure, but at ambient temperature and humidity, in order to effect exchange of glycerol for the aqueous liquid in the plant material. A dye is normally present in the glycerol to compensate for the colour changes caused by the glycerol. However, this technique does not preserve the natural colour of the plant material and does not overcome the problem of bleeding of glycerol in conditions of high relative humidity. In an alternative approach, U.S. Pat. No. 3,895,140 describes the introduction of glycerol into plant material by immersing the plant material in a hot aqueous solution containing 40 to 60% by weight of glycerol and maintained at a temperature of about 70.degree. C. Under these conditions a satisfactory preserved product is obtained after treatment for about 35 to 55 hours. Optionally, the plant material is immersed in the aqueous glycerol at temperatures above 100.degree. C. and at elevated pressure in an autoclave. This reduces the treatment time to 6 to 12 hours. However, the resulting product containing glycerol does not have stable colour and is prone to bleeding. The lengthy treatment times result in very substantial extraction of the natural green colour from the plant material.
Although glycerol remains the preservative of choice for fresh plant material, the substantial drawbacks of glycerol have led some workers in the field to seek alternative preservative compounds. For example, WO91/03160 describes a method of treatment to preserve cut flowers which comprise the steps of, first, drying the flowers over a molecular sieve, fo

REFERENCES:
patent: 3895140 (1975-07-01), Sheldon et al.
patent: 4287222 (1981-09-01), Robinson
patent: 4664956 (1987-05-01), Dokkestul et al.
patent: 4808447 (1989-02-01), Baker
patent: 4828890 (1989-05-01), Tiedeman et al.
patent: 4980194 (1990-12-01), Allison et al.
patent: 5399392 (1995-03-01), Sellegaard

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