FIELD OF THE INVENTION
The present invention is directed to a process for preserving
post harvest produce by coating the same with a coating composition capable of controlling
the transmission of gasses and water vapor into and out of the produce during maturation
and/or ripening of the produce.
BACKGROUND OF THE INVENTION
Current techniques for the preservation of fresh post-harvest
produce include temperature and/or pressure treatment, controlled atmosphere packaging,
wax and similar coating techniques, synthetic polymer coating techniques, polymer
packaging and genetic engineering of various metabolic pathways that cause ripening.
Various coating compositions have been proposed, e.g.,
a petroleum solvent solution of a waxy film former and a fungicide (U.S. Pat. No.
4,006,259); a mixture of lard, tallow, and lecithin applied in molten state (U.S.
Pat. No. 4,207,347); hydrogenated jojoba oil (U.S. Pat. no. 4,356,197); a salt of
carboxylic acid and an alkyl amine (U.S. Pat. No. 4,532, 156); a 3% oil-in-water
emulsion of hydrogenated vegetable oil, stearic acid, and anionic emulsifier, (U.S.
Pat. No. 4,649,057); the combination of a food acid, and edible reducing agent and
a carbohydrate thickener followed by freezing (U.S. Pat No. 4,751,091); a denatured
proteinaceous solution of soybeans, wheat and corn (U.S. Pat. No. 5,128,159); simultaneously
scrubbing and drenching with a liquid containing fungicide (U.S. Pat. No. 5,148,738);
a slurry consisting of by products of the produce and certain sugars and acids (U.S.
Pat. No. 5,364,648); a mixture of a polysaccharide polymer, a preservative, an acidulent
and emulsifiers (U.S. Pat. Nos. 5,198,254 and 5,376,391); and, a light activated
composition (U.S. Pat. No. 5,489,442).
Various forms of produce packaging are disclosed, by the
way of example, in U.S. Pat. Nos. 4,769,262; 5,030,510; 5,093,080; 5,160,768, 5,427,807;
5,547,693; and 5,575,418.
Some Russian and Japanese publications have proposed the
use of polyvinyl alcohol as a gas barrier coating for produce, but few if any of
these suggestions have found their way into the commercial market.
U.S. Pat. Nos. 6,165,529 and 6,203,833 commonly owned by
the assignee of this application, disclose highly improved processes for preserving
fresh produce and coating compositions therefore comprised of substantially hydrolyzed
cold water soluble polyvinyl alcohol, low molecular weight cold water soluble starch,
and surfactant. Optional additional ingredients are plasticizer, antimicrobrials,
and antifoaming agents, preferably the starch is maltodextrin, the surfactant lecithin
or dioctyl sodium sulfosuccinate, the antimicrobrials methylparaben, and the plasticizer
OBJECTS AND SUMMARY OF THE INVENTION
An object of this invention is to provide a new, improved
and highly economical coating process for extending the shelf life of post-harvest
produce and a composition therefore.
Another object of this invention is to provide a process
for preserving postharvest produce that prolongs the period during which the produce
may be stored at ambient temperatures without significant deterioration of the produce.
A further object is to provide a process for preserving
fresh produce that delays maturation, water loss, and ripening of post-harvest produce
and therefore prolongs the duration of time between harvesting and the time in which
the produce is in prime condition for consumption.
In accordance with the invention, the new and improved
process resides in the application to the exterior surface of post-harvest produce
of an improved coating composition comprising an aqueous emulsion from 0.25 to 25
percent by weight polyvinylidene chloride copolymer, and from 0.0001 to 10 percent
surfactant, preferably Triton-X. Optional additional ingredients include antimicrobrials,
plasticizers, and antifoaming agents.
The coating composition limits but does not prevent respiratory
exchange, i.e., transmission of oxygen (air) into the produce, transmission of gasses,
e.g. ethylene and carbon dioxide, out of the produce, and water vapor transmission
to control and prolong the maturation and ripening process and, to increase the
permissible storage time between harvest and consumption.
These and other objects and advantages of the invention
will become apparent to those of reasonable skill in the art form the following
The following is a detailed description of certain embodiments
of the invention, which are presently deemed by the inventor to be the best mode
of carrying out the invention. Drawings are not deemed necessary inasmuch as the
following description will enable any person skilled in the art to make use of the
As above indicated, the invention resides in the discovery
that the application of a specially formulated coating composition to the exterior
surface of post harvest produce in particular fruits, especially those having a
peel, rind, or skin, that are not edible, significantly delays maturation, ripening,
and water loss. This in turn prolongs the duration of time between harvest and optimum
conditions for consumption so that more widespread distribution of fresh fruits
and vegetables is accommodated. Additionally, the need for specialized transportation
and storage equipment and conditions, such as refrigeration, can in many cases be
eliminated or at least alleviated.
Pursuant to the Invention, the coating composition is preferably
and most easily and economically applied to the exterior surfaces of selected fruits
and vegetables by application of a dilute liquid emulsion.
The emulsion is preferably aqueous and comprised by weight
percent (w/w) from 0.25% to 25%, preferably 1 % to 10% and more preferably 2% to
7% of polyvinylidene chloride copolymer suspended in water, and 0.0001 to 10%, and
more preferably from 0.01 % to 1 % surfactant, such as Triton-X45.
Optionally, the coating composition may also include any
or all of from about 0.05% to about 1 % antimicrobrials, preferably methylparaben,
a small amount of plasticizer, e.g., polysorbate from 0.01 % to 10% by weight of
polyvinylidene chloride copolymer; and, preferably 0.005% of an antifoaming agent,
such as polydimethylsiloxane.
The concentration of the constituents in water may range
from 0.25% to 7% by weight, i.e., the dilute solution is comprised of from 93% to
99% by weight water.
The aqueous solution may be applied to the produce in any
suitable or customary manner, e.g., by dipping the produce in the tank or vat of
the solution, by spraying the solution onto the produce, or by passing the produce
through a downwardly falling curtain or waterfall of the solution. The entire exterior
surface of the produce, or when warranted only portions of the exterior surface
of the produce, can be coated with the solution to achieve desired shelf-life extension.
When spraying coats the produce, the solids content of the composition preferably
should not exceed 20%, and more preferably 5%.
Following application of the coating from the emulsion,
the post harvest produce may be packed wet for subsequent shipping, or if desired,
the coating may be dried either in ambient air or a forced air drying tunnel.
The coating formed an the produce from the emulsion has
a degree of permeability, thereby enabling the dried coating to readily exchange
respiratory products with the surrounding atmosphere. The extent to which breathing
or respiration is accommodated i; a function of the physiological reactions of the
species of the produce and the particular chemical composition of the emulsion coating.
While not intending to be bound by any particular theory, the coating enables limited
transmission of oxygen, ethylene, and carbon dioxide gases produced during the maturation
process, or artificially exposed to the post harvest produce in specifically designed
gassing chambers. In particular the coating of the present invention significantly
reduces water vapor transmission and therefore water loss of the produce thereby
reducing and or delaying dehydration, which manifests itself in the produce as shriveling,
and reduction of size of the produce or wrinkling of the skin an the produce.
In the present invention it was found that a the polyvinylidene
emulsions used had the best results if the emulsions resulted in dried films having
gas transmissions in the following ranges, for oxygen the range was 1 to 100 cm3-µm/(m2-day-bar)
at 25°C and 85% relative humidity with the most preferred range being 10-80
cm3-µm/(m2-day-bar) at 25°C and 85% relative humidity, for water vapor
the range was 1-50 g-µm/(m2-day) at 38 °C and 90% relative humidity, with
10-30 g-µm/(m2-day) at 38 °C and 90% relative humidity being preferred.
The polyvinylidene chloride copolymers used in the present
invention can be any of the following, polyvinylidene chloride-co-, acrylic acid,
methyl acrylic acid, vinyl chloride, vinyl acetate, methyl methacrylate, propylene,
ethylene, acrylates, styrene's, or any combination of the above mention monomers
which form the copolymer composition.
To achieve the objects and advantages of the invention
and to provide an emulsion that forms a thin continuous film an the surface of the
post harvest produce that extends the shelf life of the produce, the following coating
composition, based an weight percent to water is presently preferred:
The DIOFAN A036 is the primary constituent of the coating
for controlling the gas exchange of the post harvest produce. The Triton-X45 reduces
the surface tension of the composition and facilitates the formation of a very uniform
coating an the surface of the produce, which is preferable for consistent performance.
A number of polyvinylidene chloride copolymers can be used
in the present invention such as DIOFAN A036, A736, A115, A716, 193D, A232, A050,
A063 and A603, all available commercially available (such as from the Solvay Corporation,
Solvin S.A., Specialty Polymers, Brussels Belgium).
The surfactant or wetting agent used enhances the ability
of the composition to uniformly coat and adhere the coating to waxy surfaces generally
found in post harvest produce. The Triton-X45 is more preferred but one can also
use Triton X, 15, 35, 45, 100, 102, 114, 165, 305, 405, 505, L-80N, as well as Tergitol
surfactants both of which are available from the Dow Chemical Company, Midland,
Michigan, Polysorbate known by the trade name Tween-XXX where X designates a digit
from 0 to 9 can also be used and are available from ICI America's, Wilmington, Delaware.
Dioctyl sodium sulfosuccinate from the Cytec Corporation can also be used.
Optionally, the coating composition may also include one
or more of the following: from 0.05% to %% antimicrobrials such as triclosan and
more preferably methylparaben, a fungicide from 50 to 5000 parts per billion such
as TBZ, SOPP, or Imalzalil, and a plasticizer such as glycerin or polysorbate from
0.1 % to 20% to the weight of polyvinylidene chloride copolymer in the water based
An antifoaming agent is recommended when the coating is
being applied to post harvest produce commercially. During preparation and application
of the coating without an antifoaming agent frequently results in foaming and a
consequent delay n the time of usefulness due to the elapse of time before which
the foam dissipates and the coating is ready to use. An antifoaming agent eliminates
the delay and is employed primarily as a matter of production expediency. In the
present invention 0.001 to 0.5% of an antifoaming agent can be used as polydimethylsiloxane,
known as FG-10 available form the Dow Corning Corporation, Midland, Mich.
In the case of bananas and other fruits and vegetables
having an initial preservation period between harvesting and initiation of the ripening
process and a second preservation period between initiation of the ripening process
and the time of consumption, the coating process of the invention may be employed
for purposes of preservation it either or both of the two periods.
The coating solution is appropriately prepared by mixing
deionized water to a concentrated emulsion that contains approximately 50% solids
by weight of polyvinylidene chloride copolymer to adjust to the appropriate concentration.
To that solution is added while mixing the appropriate
concentration of surfactant, biocide, and antifoaming agent to achieve the required
industrial behavior for application.
In one example of an experimental comparative test, substantially
identical green and hard but previously ungassed bananas were purchased from a local
distributor. Control bananas were coated by dipping the Same for about 10 seconds
into an emulsion containing about 5% by weight polyvinylidene chloride copolymer
DIOFAN A036 containing Triton - X45 surfactant, followed by drying in ambient air.
Other of the bananas were not treated in any manner. The bananas were then stored
in a refrigerator at 58°F for two days. Then the boxes of bananas were taken
to a distributor and placed into an ethylene gassing room for two days at approximately
72°F to accelerate yellowing or ripening and stored at ambient conditions for
the remainder of the test. A reliable method to determine the effectiveness of the
coating in delaying ripening is to observe the amount and size of brown spots or
"sugar spots" that appear an the skin of the banana. After 4 days small brown spots
appeared an the untreated bananas and became numerous and large an day 5. In contrast
hardly any brown spots appeared an the coated bananas an the polymer-coated bananas
after 6 days. And alter 7 days a significant portion of the uncoated banana skin
was brown spotted and less than 10% of the coated bananas had brown spots, which
were very smal1 in comparison. After 8 days the control bananas were mostly brown
and soft to the touch whereas the coated bananas had small brown spots and the interior
flesh was firm with no off flavors or odors when tasted. Under these particular
conditions the coated product has at least a 2-3 day better shelf life than the
In another comparative test, freshly harvested pineapples
were procured from an organic food store. One of the biggest problems with freshly
harvested pineapples is weight loss during storage and distribution. Four fresh
pineapples that had no coating were used as controls and four pineapples and crowns
of the fruit were coated with a 5% emulsion as in example 1. The fruit was held
at room temperature for 7 days after coating and weight loss was measured. After
7 days the weight loss of the control cell averaged 10.7% and that of the coated
product was 8.6% at 20% reduction in weight loss vs. the controls. To put that in
perspective that would be an increase of 20,000 pounds of product sold in a 1,000,000pound
shipment. In addition the coated fruit was firmer to the touch and the internal
flesh was not translucent and displayed no internal brown spots, which is indicative
of loss of shell life vs. the control that was translucent and had brown spots in
one half of the samples.
Additional fruits and vegetables that are likely candidates
for successful practice of the invention include, avocados, cantaloupes, honeydew
melons, mangoes, papayas, platains, star fruit, lemons, limes, oranges, tangerines,
kumquats, tangelos, grapefruits, lychee, guava, breadfruit, kiwi and rambutan.
As shown by the experimental tests, the coating process
of the invention enhances control over respiratory exchange or gas in and particular
water and water vapor transmission of the coated produce, and contributes significantly
to prolong the shelf life of the post harvest produce. Also, the coating inhibits
fungal mold growth and with appropriate additives inhibits bacterial growth an the
surface of the produce.
The objects and advantages of the invention have therefore
been shown to be attained in a convenient, economical, practical and facile manner.