PRODUCE PRESERVATION BY MEMBRANOUS COATING PROCESS

Abstract: There is provided a novel process for the preservation of fresh fruits, fresh vegetables and fresh eggs, which comprises applying to the outer skin or shell thereof, a layer of polymer which is permeable to water vapor but essentially impermeable to oxygen. To this water vapor permeable polymeric layer, there is then applied a curable coating to provide a water insoluble coating essentially impermeable to water vapor but essentially permeable to oxygen, as well as to carbon dioxide, ethylene and nitrogen, which is then cured.

Description: PRODUCE PRESERVATION BY MEMBRANOUS COATING PROCESS FIELD OF THE INVENTION Preservation of fruit, vegetables and eggs by coating for storage at ambient temperature. BACKGROUND OF THE INVENTION The preservation of fruit and vegetables in the fresh state is a problem of importance in high and low technology environments. In high technology environments, refrigeration is the mode of choice. This mode requires substantial investment in mobile and stationary plant. It does not however deal with the problem of ripening of picked fruit before it reaches a refrigeration plant, while in transit on a hot dock or spoilage in case of mechanical failure of the plant. These factors all require early picking of unripe fruit which is to be stored or shipped. Such early picked fruit does not have the high levels of sugars and esters which give locally available produce, its premium taste. Thus a preservation mode which would reduce these negative factors would be desirable. In low technology environments with high ambient temperatures, no satisfactory preservation modes for fruits and vegetables exist. Thus while growers may be able to be efficient producers, the produce cannot reach the widest possible circle of potential consumers due to spoilage in transit. It is well known that the spoilage of fruit is due, to a substantial extent, to the absorption of oxygen, the loss of water by evaporation and the retention of ethylene. Thus for example the classical preservation technique of waxing fruit, which enhances its appearance as well as, to a certain extent blocking loss of water vapor and access of oxygen, also blocks the loss of ethylene, which accelerates the ripening. It would thus be desirable to provide a coating which will prevent the absorption of oxygen and the loss of water by evaporation and block the retention of ethylene. Such a coating should either be appearance neutral or enhance the appearance, be readily removable by light scrubbing or so thin and non toxic that it would neither be noticed by the consumer nor be harmful to him. SUMMARY OF THE INVENTION here is provided a novel process for the preservation of fresh fruit, fresh vegetables and fresh eggs, which comprises applying to the outer skin or shell thereof, a layer of polymer which is permeable to water vapor but essentially impermeable to oxygen. This polymeric material, which is preferably, but not critically water soluble, is derived from at least one group of monomeric units having at least one substituent of sufficient lability to form at least a hydrogen bond or be subject to an addition reaction or condensation reaction after polymerizationin which these substituent groups may also form covalent bonds. To this water vapor permeable polymeric layer, there is then applied a curable coating to provide a water insoluble coating essentially impermeable to water vapor but essentially permeable to oxygen, as well as to carbon dioxide, ethylene and nitrogen. As the water permeable polymer there may be mentioned polymers derived from vinyl acetate (PVA), acrylonitrile, acrylic acid, acrylates or the monomers of carboxymethyl cellulose (CMC) and cellulose acetate (CA). The polymers may be copolymers of these and other monomeric units such as those carrying the amino, carbonyl or sulfone moiety. A second coating, when cured provides, suitably a film of polysilane or polysiloxane which is bonded to the water vapor permeable layer either directly by hydrogen or covalent bonding, or similarly through intermediate cross linking agents. This curable coating is suitably a substituted silane monomer or oiigomer or a substituted siloxane oiigomer carrying more than least two funconalities per moiety, which upon cure form the aforementioned type of film. It will be understood by those skilled in the art that a tri- or polyfunctional silane or siloxane constituent is required for cross linking, which is important for the formation of a complete coating. Such trifunctional material when cured, tend to be brittle. Cured bifunctional materials are flexible but do not cross link. Thus it is desirable to utilize a siloxane or silane oiigomer, or suitably a siloxane oiigomer of two functionalities, in the presence of a small amount, suitably about 1 to about 10 % w/w of a tri or poly functional silane or siloxane. At least one of the constituent moieties of the water permeable polymer suitably possess least two function selected from the group consisting of the carbonyl, carboxyl, hydroxyl, amino, sulfone, nitrile alkenyl and ester functions. These functions can either react directly with the applied silane or siloxane, for example by addition or condensation reactions, with or without the presence of a catalyst, to form hydrogen bonds therewith, form chemical bonds or react with a cross linking agent which in turn reacts therewith in a similar manner. The water vapour permeability, combined with oxygen blocking, of the polymer is substantially controlled by the presence of a pore forming agent, which can also act as a cross linking agent between the layers. This pore forming agent is not the same as the catalyst (discussed below) for the polymerization of the outer film, though the effect may be similar. The pore forming agent may be boric acid and alkanoic alkanpolyoic acids and hydroxy derivatives thereof having at least three carbon atoms, suitably lactic acid, tartaric acid, gluconic acid and citric acid. Boric acid is however preferred. The simplest way of applying the first layer is as a solution, suitably as an aqueous solution which may also contain the pore forming agents as well as a catalyst for the reaction with the functionalities of siianes and siloxanes. Depending on the reaction to be catalysed, there may be used an acid, base or metallic salt catalysts such as a chlorplatinic acid catalyst or a food grade tin alkyl catalyst. The siianes and siloxanes which are utilized as the coating may contain similar or different functionalities. This coating ,when cured, should not only block the passage of water vapor, but should be water insoluble, so that its integrity will not be impaired if the fruit becomes wet during shipment. Suitable functional groups include halo, hydride, hydroxy, alkoxy, amino, alkyl or dialkyl amino, acyloxy or the like. The amino and halo functions, while operative, generate hydrogen halide and ammonia in the curing step, both of which are environmentally undesirable. Similarly, alkoxy groups will generate alkanols. Thus hydride and hydroxy groups which, depending on the group with which they react, generate nothing or water, hence are preferred. The hydroxy function need not be initially present but may be in the form of a precursor hydrolyzable thereto by acid or water. In this case a solution of the precursor may be applied in the presence of such water or acid. For example, precursor may be an alkyl trialkoxysilane in the presence of a lower alkanoic acid or a tin catalyst. Suitably, the applied siianes or siloxanes will be substituented by non labile moieties. For example, lower alkyl of 1- 5 carbons, i.e. ethyl or methyl. Lower alkenyl of 2-5 carbons, such as vinyl, may fall in this category, but it should be noted that alkenyl groups may be subject to addition reactions. Thus their copresence with hydride groups may not be desirable. Depending on the nature of the functionalities, the silane or siloxane monomer or oiigomer may be applied in undiluted form, i.e. as a dip or spray, or similarly in the form of a solution or emulsion. Where the solution is an aqueous solution the level of solubility therein may be quite low. Since only a thin film is required it is enough that the level of solubility is at least 1% w/w, though at least 5% w/w would be more desirable. Needless to say where the silane or siloxane functionalities include amines or halo, aqueous solutions or emulsions are not suitable. The cure, that is to say definite bonding with the first layer and, if applicable, cross linking, may be effected in several ways. The simplest, but most time consuming is by air drying at ambient temperatures. This mode can be employed in energy poor areas where time is not of the essence and where investment capital for rapid cure equipment is scarce. The cure may also be effected by air drying at ambient temperatures in a wind tunnel, by air drying at elevated temperatures up to about 50 °C or a combination thereof. These curing modes should be considered illustrative but not limiting except that the application of high temperatures for extended time periods is not recommended since such conditions would at least partially cook the items to be preserved in the fresh state. While the outer silicone coatings of the present invention are insoluble in water, it is nevertheless possible to remove them with water if desired. The inner coatings are water soluble. Thus a modest amount of abrasion (but more than that encoundered in conventional packing operations) will break the outer layer sufficiently to permit water to contact the inner, water soluble layer. Such penetration will permit dissolution of the inner layer and thus aid in the removability of the outer coating, if desired. DESCRIPTION OF THE PREFERRED EMBODIMENTS The starting material for the process is freshly picked externally clean fruit or vegatables which are free from any visable deterioration of either the inner content or the skin thereof. While the subsequent discussion will be directed to fruit, it is equally applicable to the preservation of shell eggs. The fruit which may be preserved by this method include cherries, apples, peaches, pears, oranges, tangerines, grapes and the like. Vegetables include onions, potatoes, yams, broccoli, tomatoes leaf and Jerusalem artichokes and the like. This listing is for puposes of exemplification and not limitation The water permeable coating is, suitably, applied as a dilute aqueous solution. The absolute concentration of the solution is not critical. However, it has been found that a 1-8% w/w solution is operative and satisfactory. The molecular weight range is again not critical. However, it has been found suitable to use PVA in the molecular weight range of 9-300 Kd, preferably about 170 Kd celluose acetate in the range of 3Kd to 150Kd, suitably about 5Kd and CMC in the range from about 10 Kd to about 150Kd, suitably about 30Kd to about 50Kd. The solution containing this polymer may also contain a number of additional constituents. The most important of these constituents is the pore forming agent (PFA). The PFAs are weak acids and should be present at a level of between 0.01 and 0.4 % by weight of the amount of the total solution. It is especially preferred that the PFA be present at a ratio of about 0.1% by weight. It is important that these levels of PFA not be exceeded otherwise precipitation of polymer may occur. The exact mechanism of action of the PFA is not fully understood. However, in addition to its pore forming function it is believed that the PFA acts as a cross- linking agent either by covalent or hydrogen bonding between the functionalities of the water vapor permeable polymer and the outer, water impermeable coating. The PFA may be an inorganic acid such as boric acid or an organic acid suitably an alkanoic or alkanpolyoic acid which may, if desired, have hydroxyl groups attached thereto. Again for reasons which are not fully understood it is preferred that the acid utilized be, at ambient tempertures, a solid rather than a liquid and have at least three carbon atoms. It will be recognized that certain acids falling in this category may not have the desirable odors for example, certain butyric acids. These are to be avoided for esthetic rather than chemical reasons. A further, desirable, constituent of the solution would be a surfactant. Any food acceptable surfactant may be employed as examples thereof may be mentioned polyoxyethylene and surfactants of the Tween family. These are utilized in amounts in substantially the same weight range as the PFA that is to say, between 0.1 and 0.4 % by weight of the total solution, most suitably, about 0.1 % by weight. Further optional additivies to the solution include conventional preservatives, antibiotics and mold and yeast inhibitors. Any conventional agents may be used such as lower alkyl p-hydroxy benzoates, of these propyl, iso propyl, butyl and iso butyl p-hydroxy benzoates may be mentioned. However, sorbic acid has been found both inexpensive and acceptable. The amount thereof, is again similar to the amount of PFA. There may also be utilized an anti-oxidant, for example vitamin C. Preservatives and antioxidants may be utilized at a level of between 0.1 and 0.4% by weight of the total solution. A growth stimulant such as, for example, 2,4-D otherwise known as 2,4- dichlorophenoxy acetic acid or trinoxol may also be added. Since the acid itself is substantially insoluble in water the sodium salt may be employed. It should be noted that this material is not univerally accepted for human food use and where it is not so permitted, it should not be utilized. It is not a critical component of the invention. When utilized, the growth stimulant may be present at a level of about 0.01 to 0.03 % by weight of the total solution, as stated above. Further useful constituents of the solution are catalysts for the reaction of silane or siloxane functionalities with labile groups such as vinyl or hydroxyl on the water vapour permeable layer. Such catalysts include chlorplatinic acid and food grade tin catalysts suitably tin soaps, such as dibutyl tin dilaurate, diacetate or 2- ethylhexanoate the first being present as about 0.001% , the latter group as about 1 - 1.5 % by weight of the total solution. The former catalyses the addition reaction of hydride to vinyl and the latter catalyses the condensation of silanol or alkoxy siianes with hydroxy. Polymer containing solution is prepared by dissolving the polymer in water at a temperature of about 50 - 100 °C to a concentration of about 10 to about 15 % w/w. The remaining constituents are separately dissolved in water at about 20 to about 50 °C and stirred vigorously. The polymer solution is then added thereto until a homogeneous mix is obtained. More water may be required to bring to the desired concentration. The solution is then cooled to ambient temperature before use. The condensation of silanols or alkoxy siianes with hydroxy may also be catalysed by acid or base. Clearly if the PFA is one of the above mentioned acids, it will serve as a catalyst. A base, suitably an amino base such as a tertiary amine or alkanolamine suitably triethanolamine may be present in similar amounts. In order for the preservation process to be as effective as possible it is desirable that the water vapor permeable coating be applied as soon as possible after the picking of the fruit. Thus, suitably, the fruit should be washed and immersed in the solution within six hours of picking. Since the solution is an aqueous solution it is not necessary to totally dry the fruit before application of the solution since, the minor amount of wash water which it carries, will not negatively effect the coating step. Depending upon the facilities available, the application may be by spraying or dipping. In either case facilities should be provided to permit the excess solution to drain off the fruit. The coated polymeric solution is then dried. The procedure used is dependent upon the facilities available. The coating, at ambient temperatures of from about 20-30 °C will set enough for the next stage in from about 2-5 hours. The process may be accelerated by drying in a wind tunnel. However, since the fruit, or the eggs, should not be "cooked" temperatures should not exceed 50 °C and it is desirable to maintain tempertures below 40 °C, if possible. When the fruit is dry to the touch the water impermeable layer is applied. While the ultimate effect is substantially the same, three approaches may be taken to applying this coating depending upon the materials and application technology available. The most preferred mode is the application of a siloxane or siloxane oiigomer of moderate molecular weight, suitably, but not critically of 10 to 300 silicon units having two functionalities per oiigomer. There are also present, to the extent of from about 0.1 to about 15 % w/w, of the foregoing oiigomer, at least one monomer or oiigomer having at least three functionalities attached thereto. The preferred difunctional silyl siloxanes or siloxanes have the general formulae I - IV: I Z.SiR 2 .[Si0 2 ] n .SiR 2 Z II R 3 .Si.[(Z)SiOR] 2 .[SiOR 2 ] n .SiR(Z).SiOR 3 III Z.SiR 2 .[(Z)SiO.R 2 ] n .[R.SiO.(Z)].SiOR 3 (while the functionalities in II are shown as blocks this is merely preferred and not critical), a poly or tri functional components there may be used compounds of the formulae: IV Si.Z 4 V R.Si.Z 3 VI R.Si.Z 2 .[SiO.R 2 ] n .SiO.Z 2 .r VII R 3 .Si.[(Z)SiO.R] x .[SiO.R 2 ] m .SiO.R 3 (x >2) wherein Z is a reactive moiety such as halo, suitably chloro, hydroxy, hydride, amino or alkoxy (depending on the intended reaction) and n is an integer from 1 through 300 suitably, 50 to 300 and R is an unreactive moiety suitably, an alkyl, alkenyl or aryl moiety. The values of R need not be the same. The foregoing small grouping is illustrative only and neither critical nor limiting. Compounds of similar structure are widely known to those skilled in the art and readily available either by purchase or synthesis. In technologically advanced countries these materials are readily available. It is especially preferred to utilize siloxanes carrying terminal hydoxy groups. These materials are totally non-hazardous to the general environment as well as to the workers handling them, have a rather low molecular weights and levels of viscosity and are unreactive in the absence of catalysts. They are therefore, most suitable for application by dipping, or more preferably, spraying directly i.e. without the need for dissolution in a solvent, onto the fruit previously coated with the water permeable polymer which contain any of the aforementioned catalysts or cross linking agents. Reaction at ambient temperature is not very rapid. However, this is not a major problem as only thin coatings are required with the hydroxyl moieties on the water permeable layer as well as, cross-linking between the remaining hydroxyl moieties in the silane or siloxane. Thus, the unutilized material which drains off the fruit and is not a part of the coating may be readily recycled. The cure is substantially accelerated by raising the temperature up to about 50 °C or in the presence of a suitable catalyst, such as tin, titanate or the like Materials where Z is hydride may also be utilized in a similar manner. These compounds are exceedingly reactive with hydroxyl groups in the presence of catalysts. Thus, the material itself need not be carefully isolated from moisture both before and during use and the water permeable polymer layer need not be totally dry. The hydride will react with the water hydroxyls generating a silanol which will then react with the hydroxyl groups either on the PFA, or the polymer itself which, in turn, would create an adhering polysiloxane or polysilane layer. It will be understood that in certain areas neither of the foregoing groups of materials are available, nor would facilities therefore handling them be available. Nevertheless, the process can still be carried out in a procedure where the starting material is an di-alkyl silyl-diether for example, diethyl-diethoxy silane, dimethyl- dimethoxy silane, or a triether such as ethyl-triethoxy silane, vinyl-triethoxy silane and silyl ester such as vinyl-triacetoxy silane. These silyl ethers or esters are hydrolyzed in water or in the presence of a mild acid suitably, propionic or acetic acid. This gives rise to the corresponding hydroxy alkyl silane which is not stable and condenses to the corresponding siloxane oiigomer with hydroxy groups in about 4 to about 12 hours at ambient temperature. At this point it is advisable to remove alkanol which is produced . This is best done either by application of reduced pressure without heat or by ultrafiltation with a filter of less than 600 angstrom pore size. This may also remove the acid thus acidity adjustment to 6<pH <4 may be required. This siloxane oiigomer is also not stable and will either condense with itself or with other hydroxyl groups in a period of from about 12 to about 72 hours. Thus it is advisable to apply the siloxane solution about 12 hours after initial preparation. It has been found that where this siloxane oiigomer in aqueous solution, has been applied to fruit bearing the aforementioned water/vapor permeable layer with labile groups preferably hydroxyl but also including carboxyl, nitrile and ester attached thereto, bonding will occur. Where a PFA such as boric acid is present, this will be covalent bonding. Hydrogen bonding to hydroxyls present in the water vapour permeable layer may also occur. The total reaction time at ambient temperature that is to say, between 20-40 °C is about 4 to 12 hours. Thus, in this embodiment the di-alkyl di-alkyloxy silane is brought to a pH above 4 with acetic acid, the fruit dipped therein, drained, and allowed to cure under ambient conditions for 4 to 12 hours. The permeabilities of the membranes to various gases are shown in Table P below: TABLE P Permeation coefficients of various Gases (10 "8 cm 3 /(cm. sec/cm. Hg) 0 2 H 2 0 C0 2 C 2 H 4 N 2 PVA Membrane 0.98 21.15 4.15 N/A 1.32 Si Membrane 71 0.74 434 165 36 EXAMPLES Example I Solution A Material Weight in Water polyvinyl alcohol 5% (polymerization degree: 1000 hydrolytic degree:99%-99.8%) boric acid (Mn=61.83) 0.5% Tween 0.1% sorbic acid 0.1% 2,4-D growth stimulant 0.01% vitamin C 0.04% Solution B ethyltriethoxy silane 2.5% sorbic acid 0.15% propionic acid for adjusting PH> =4 Solution A is prepared by dissolving the PVA in water at a temperature of about 70°C to a concentration of about 15 % w/w. The remaining constituents are separately dissolved in water at about 30 °C and stirred vigorously. The PVA solution is then added thereto until a homogeneous mix is obtained. More water may be required to bring to the desired concentration. The solution is then cooled to ambient temperature before use. Solution B is mixed at ambient temperature, after 12 hours it is passed through an ultrafilter with pore size less than 600 angstroms and the alkanol discarded. Fresh tangerines are picked, washed and within six hours of picking are dipped into solution A and are left to dry in ambient conditions (30 °C) for six hours. The coated fruit was then immersed in solution B and similarly, set to dry under ambient conditions for twelve hours. Samples of the fruit were then stored at ambient temperture for seventy (70) days (the results are summarized in Table I below). At the end of seventy (70) days the coated fruit had a fresh appearance and a fresh taste when eaten. The non-coated fruit had become dried out and were inedible. TABLE 1 Sample Wt. Rate of Number weight (Baskets) loss 20 days 30 days 60 days 70 days 1 1258 g 1207 g 1203 g 1200 g 1191 g 5.3% 2 1760 g 1714 g 1708 g 1701 g 1693 g 3.8% 3 1904 g 1861 g 1845 g 1850 g 1842 g 3.2% 4 1474 g 1429 g 1425 g 1407 g 1401 g 4.9% 5 1646 g 1604 g 1600 g 1591 g 1580 g 4.0% Control 1848 g 1808 g 1701 g 1634 g 1582 g 14.4% EXAMPLE 2 Solution A Material Weightinwater (%) PVA 8% boric acid 0.2% polyoxyethylene 0.2% sorbic acid 0.15% 2,4-D growth stimulant 0.02% Vitamin C 0.02% Solution B ethyltriethoxy silane 1% sorbic acid 0.1% propionic acid for adjusting PH > =4 Solutions A and B are made up as in Example 1. Fresh apples are picked, washed and within six hours of picking are dipped into solution A and are left to dry in ambient conditions (30 °C) for six hours. The coated fruit was then immersed in solution B and similarly, set to dry under ambient conditions for twelve hours. Samples of the fruit were then stored at ambient temperture for seventy (70) days (the results are summarized in Table II below). At the end of seventy (70) days the coated fruit had a fresh appearance and a fresh taste when eaten. The non-coated fruit had become dried out and were inedible. TABLE 2 Weight 10 days 30 days 60 days 90 days 120dys Sample 178 g 161 g 159 g 157 g 156 g 156 g Control 181 g 172 g 168 g 154 g (mouldy) 15 days wt. Rate of wtloss Sample 155 g 3.7% # Since the fruit is wet initially, Control n/a n/a rate is derived from wt. loss from day 10 - 150. EXAMPLE 3 Solution A Material Weight in Water PVA 4% boric acid 0.4% Tween 0.2% sorbic acid 0.1% honey 0.2% Solution B ethyltriethoxy silane 1% sorbic acid 0.1% using propionic acid to adjust PH > =4 Solutions A and B are made up as in Example 1. Fresh pears are picked, washed and within six hours of picking are dipped into solution A and are left to dry in ambient conditions (30 °C) for six hours. The coated fruit was then immersed in solution B and similarly, set to dry under ambient conditions for twelve hours. Samples of the fruit were then stored at ambient temperture for seventy (70) days (the results are summarized in Table III below). At the end of seventy (70) days the coated fruit had a fresh appearance and a fresh taste when eaten. The non-coated fruit had become dried out and were inedible. TABLE 3 0 10 days 30 days 60 days 90 days 120 days 150 days rate Sample 149 g 134 g 131 g 130 g 129 g 129 g 128 g 14% Control 149 g 136 g mouldy In accordance with the above procedure, but where, in place of boric acid, there is used lactic acid or citric acid in similar amounts, a similar result is obtained. EXAMPLE 4 Solution A Material Weight in water (%) CMC (M.W. 5000) 8% boric acid 0.2% polyoxyethylene 0.2% sorbic acid 0.15% Chlorplatinic acid 0.02% Vitamin C 0.02% Solution B Me 3 Si(SiO.Me.H) 40 .SiO.Me 3 spray Solution A is made up as in Example 1 except that CMC is used in place of PVA. Fresh eggs washed and within six hours of laying are dipped into solution A dried in an air oven at 50 °C and air velocity of 500 m/min for 10 minutes. The coated fruit was then sprayed with the siloxane ("solution" B) and similarly dried. EXAMPLE 5 Solution A Material Weight in water (%) CA (M.W. 5000) 5% boric acid 0.2% polyoxyethylene 0.2% sorbic acid 0.15% Di butyltin dilaurate (Food grade) 0.02% Vitamin C 0.02% Solution B (Me 2 Si.OEt) 2 .(SiO.Me 2 ) 200 spray [Me 2 Si.(OEt) 2 ] (20:1) spray Solution A is made up as in Example 1 except that CA is used in place of PVA. Fresh carrots are picked, washed and within six hours of picking are dipped into solution A dried in an air oven at 50 °C and air velocity of 500 m/min for 10 minutes. The coated carrots are then sprayed with the silylsiloxane ("solution" B) and similarly dried. EXAMPLE 6 Solution A Material Weight in water (%) CMA (M.W. 5000) 8% lactic acid 0.2% polyoxyethylene 0.2% sorbic acid 0.15% Vitamin C 0.02% Solution B Me 3 Si.[SiO.Me.OMe] 4 .[SiO.Me 2 ] 150 Solution A is made up as in Example 1 except that CMC is used in place of PVA. Fresh onions are picked, washed and within six hours of picking are dipped into solution A, dried in an air oven at 50 °C and air velocity of 500 m/min for 10 minutes. The coated onions are then sprayed with the silylsiloxane ("solution" B) and similarly dried.

Claims: I Claim 1. A process for the preservation of fresh fruit, fresh vegetables and fresh eggs, which comprises applying to the outer skin thereof a first layer of ingestible polymer, derived from at least one group of monomeric units at least one member of said group having at least one substituent of sufficient lability to form at least a hydrogen bond, be subject to an addition reaction or a condensation reaction after polymerization, permeable to water vapor but substantially impermeable to oxygen, applying to said water vapor permeable polymeric layer, a curable coating selected from the group consisting of a substituted silane monomer or oiigomer or a substituted siloxane oiigomer having a functionality greater than two per silane or siloxane moiety, capable of bonding by at least hydrogen bonding, being subject to an addition reaction or a condensation reaction, with said at least one labile substituent of said water permeable polymer and curing said curable coating to provide a water insoluble, ingestible coating, essentially impermeable to water vapor but essentially permeable to oxygen, carbon dioxide, ethylene and nitrogen. 2. A process of claim 1 wherein the labile substituents on said water permeable polymer are selected from the group consisting of the vinyl, carboxyl, carbonyl, amino, hydroxyl, nitrile, sulfone and ester functions. 3. A process of Claim 2 wherein at least one of the monomers forming said water permeable polymer is selected from the group consisting of vinyl acetate, acrylonitrile, acrylic acid, acrylates and the monomeric units of carboxymethyl cellulose and cellulose acetate. 4. A process of claim 1 wherein the water permeable polymer is applied as a solution of polymer further comprising a pore forming agent. 5. A process of Claim 3 wherein the solution is an aqueous solution. 6. A process of claim 3 wherein the pore forming agent is selected from the group consisting of boric acid and alkanoic, alkanpolyoic acids and hydroxy derivatives thereof having at least three carbon atoms. 5 7. A process of claim 4 wherein the pore forming agents are selected from the group consisting of boric acid, lactic acid gluconic acid, tartaric and citric acid. 8. A process of claim 5 wherein said solution further comprises a catalyst for 10 condensation reaction between said siianes and siloxanes and said at least one labile substituent on said at least one constituent unit of said water permeable polymer . 9. A process of Claim 8 wherein the catalyst is an acid, a base, platinum salt catalyst or a food grade tin catalyst. 15 10. A process of claim 1 wherein the functionalities on the siianes and siloxanes are selected from the group consisting of halo, hydride, hydroxy, lower alkoxy of 1- 5 carbons and primary and secondary amino, acyloxy or oximino. 20 11. A process of Claim 10 wherein halo is chloro and alkoxy is methoxy or ethoxy. 12. A process of Claim 1 wherein the curable coating is a hydrolyzed precursor for a silicone containing a hydroxy substituent or a hydroxy containing group in the presence of a hydrolyzing agent to effect said hydrolysis. 25 13. A process of Claim 1 wherein the silane or siloxane monomer or oiigomer is applied in the form of a solution or emulsion. r 14. A process of Claim 12 wherein the silane or siloxane monomer or oiigomer is 30 applied in the form of an aqueous solution provided it is soluble therein to the extent of at least 1% w/w. 15. A process of Claim 12 wherein the silane or siloxane monomer or oiigomer is applied in undiluted form. 16. A process of Claim 12 wherein the siloxane monomer or oiigomer is applied in the form of an aqueous solution of a precursor hydrolyzable thereto by acid, in the 5 presence of such acid. 17. A process of Claim 16 wherein the precursor is an alkyl trialkoxysilanβ in the presence of a tin soap. 10 18. A process of Claim 1 wherein the cure is effected by air drying at ambient temperatures. 19. A process of Claim 17 wherein the cure is effected, by air drying in a wind tunnel. 15 20. A process of Claim 1 wherein the cure is effected by air drying at elevated temperatures up to about 50°C. 21. A fruit carrying a coating applied by the process of claim 1. 20 22. A vegetable carrying a coating applied by the process of claim 1. 23. An egg carrying a coating applied by the process of claim 1. 25

Inventors: WANG YING, WANG, YING
Applicants: INT APPLIED SCIENCES INC, INTERNATIONAL APPLIED SCIENCES, INC.
Application year: 1990
Main classification: A23B7
IPC codes: A23B5, A23B7, A23L1