Provided is a composition and methods for reducing the weight loss and/or preserving the natural gloss of post-harvest edible plant matter. In particular, the methods including applying to the surface of the plant matter a composition including an edible wax having a melting temperature below 70° C.; a hydrocolloid; a fatty acid; an emulsifier; and water, wherein said edible wax is present in a weight percent ranging from about 10% to about 25% of the total weight of the composition.
Description
FIELD OF THE INVENTION
The present invention relates to a composition and methods for extending the shelf life of edible plant matter by reducing postharvest weight loss while preserving the external glossy appearance of the plant matter, in particular fruits and vegetables.
BACKGROUND OF THE INVENTION
Edible coatings, which are defined as thin layers of wax or other substances applied to the surface of food, have been employed for over 800 years to increase the shelf life of food. In the United States, wax coatings have been utilized commercially since 1930s, when oranges were coated with melted paraffin waxes. These early coatings were used to produce the appearance of a glossy skin. In recent years, coatings have been used to preserve attributes connected with fruit and vegetable quality and affording shelf-life extension involving a decrease in weight loss and respiration rate while providing glossy appearance and the possible prevention of damage induced by insect penetration (Nussinovitch in Modern biopolymer science: bridging the divide between fundamental treatise and industrial application, Kasapis et al. (Eds.), New York Academic Press, Elsevier Inc., 295-326, 2009).
Pepper fruit (Capsicum annuum L.) is naturally hollow and is therefore characterized by limited water reservoir capacity. Accordingly, the loss of small amounts of water may result in loss of freshness and firmness, a reduction in fruit quality, shelf life and market value (Maalekuu et al., J. Am. Soc. Horticult. Sci., 130, 735-741, 2005). The major factor shortening the postharvest life of bell peppers is water loss (Maalekuu et al., Adv. Horticult. Sci., 17, 187-191, 2003). Once the fruit is harvested, its tissue may rapidly dehydrate since the water potential (Ψ), which quantifies the water content of the surrounding air, is much lower than that of the plant tissue thus causing the diffusion of water from the fruit tissue to the environment. Consequently, postharvest shriveling of the fruit occurs (Dijkink et al., Postharvest Biol. Technol., 32, 311-320, 2004). Flaccidity, shriveling, wilting and decay are major problems that decrease marketability and consumer acceptance of postharvest bell pepper fruit. Flaccidity is also directly associated with the loss of water during storage when respiration as well as diffusion of water through the cuticle occur. Shriveling and wilting are processes which are evident in water loss of 5% or more. Hence, reduction of water loss, especially through diffusion through the cuticle, would help maintain textural quality and external appearance of the fruit thus improving its storage life.
Achieving water-saturated atmosphere around the fruit by individual-seal, shrink-wrap or modified-atmosphere packaging (MAP) has been employed. Bell peppers individually wrapped in plastic film showed marked reduction in weight loss and softening, which resulted in an extended shelf-life. Although individual-seal and MAP appeared to reduce bell pepper fruit moisture loss, a number of limitations inhibited commercial use. One limitation that has been encountered is the development of aerobic microorganisms due to water condensation caused by temperature fluctuations during storage or transportation. It was noted that film wrapping increased the incidence of bacterial soft rot in bell pepper compared to non-wrapped peppers. It was also shown that shrink-wrapped pepper developed higher populations of total aerobic microorganisms, yeasts, and molds as compared to non-wrapped peppers. Another limitation involved environmental apprehensions about the use of plastic materials. Hence, replacement of plastic films with edible or biodegradable materials is attractive from an environmental perspective.
The most common methods used nowadays for reducing water loss of postharvest fruit include lowering the temperature and/or raising the relative humidity (RH) of the storage environment. However, these storage environments can cause chilling injury, enhance disease development and increased incidence of fruit decay. In general, it is relatively difficult to preserve the quality of postharvest bell peppers as compared to other fruits, due to the peppers’ sensitivity to low temperatures (<7° C.), water loss and rot development (Meir et al., Postharvest Biol. and Technol., 5, 303-309 1995).
The application of edible coatings and films in fruits and vegetables has received awareness worldwide for improvement of postharvest life (Lerdthanangkul et al., J. Food Sci., 61, 176-179, 1996; Conforti et al., Food Chem. Toxicol., 67, 1360-1363, 2002; Ozden et al., Euro. Food Res. Technol., 214, 320-326, 2002; Ayranci et al., Food Chem., 87, 339-342, 2004; Beaulieu et al., Indust. Crops and Products, 30, 271-275, 2009; Sabularse et al., Int. J. Food Sci. Nutri., 60, 206-218, 2009). However, despite their advantages, edible coatings for fruits can also adversely affect their quality. For example, an edible coating used to reduce the rate of water loss might interfere with fruit’s respiration, resulting in off-flavors (Park, Trends Food Sci. Technol., 10, 254-260, 1999; Chen et al., Food Hydrocolloids, 14, 561-568, 2000). In addition, the surface gloss of food is a very important parameter since it reflects on its quality in the eye of the consumer. Bell peppers have very high natural gloss levels compared to other fruits (Nussinovitch et al., Lebensmittel-Wissenschaft und-Technologie, 29, 184-186, 1995). When very glossy surfaces, such as those of red bell pepper, are treated with available coating formulations, their natural shine may be diminished.
U.S. Pat. Nos. 6,299,915 and 6,068,867 to one of the inventors of the present invention disclose a hydrocolloid protective coating for food and/or agricultural products comprising dried hydrocolloid gel, one or more natural compounds isolated from the surface of said product or a compound substantially equivalent thereto and other optional additives. The protective coating provides improved protection of the product, thereby extending its shelf-life.
U.S. Patent application No. 2004/0146617 and U.S. Pat. No. 7,222,455 disclose methods for suppressing cracking, stem browning, and water loss in fruit or vegetables, such as cherries. The methods comprise applying to fruit or vegetables an amount of a wax emulsion comprising a matrix of complex hydrocarbons, one or more emulsifying agents, and water. In some embodiments, the wax emulsion comprises from about 0.125% to about 25% (weight/weight) of carnauba wax, from about 0.1% to about 16% (weight/weight) of oleic acid, and from about 0.03% to about 6% (weight/weight) of morpholine, and from about 53% to about 99.7% (weight/weight) of water.
Edible coatings on fruits can serve as gas or moisture barriers. They can help diminish moisture loss, and/or reduce fruit oxygen uptake from the environment and thus slow respiration. Edible coatings have been reported to be effective on various kinds of fruits and vegetables (U.S. Pat. Nos. 7,771,763 and 7,169,423). Chitosan coating reduced weight loss, respiration rate, loss of color, wilting, and fungal infection of bell pepper during storage at 13° C. and 20° C. at 85% RH (El Ghaouth et al., Journal of Food Processing and Preservation, 15 (5), 359-368, 1991). Although several attempts have been made to design edible coatings for bell pepper fruit, two main problems remained unsolved. First, the coating provided only ˜4% reduction in the weight loss of the coated commodity and second, the coating reduced the natural gloss of the pepper.
There remains an unmet need in the art for an edible coating of bell pepper which provides an extension of its shelf life without impairing the natural gloss and taste thereof.
SUMMARY OF THE INVENTION
The present invention provides an edible hydrocolloid-wax based composition useful for coating plant matter, particularly a fruit or a vegetable having a high natural gloss and limited water reservoir capacity, the composition comprising an edible wax having a melting temperature below 70° C., a hydrocolloid, a fatty acid and an emulsifier. The composition of the present invention extends the shelf life of plant matter coated with the composition by reducing the plant’s postharvest water loss while maintaining the natural glossy appearance of the plant matter, preferably by brushing or polishing the coated commodity.
The present invention is based in part on the unexpected finding that coating of fruits and vegetables having natural gloss with a composition comprising a wax having a melting temperature below 70° C. in an amount of at least 10% by weight of the composition and less that 1% of a non-gelling hydrocolloid, significantly reduced the postharvest water loss of the fruits and vegetables, without affecting their taste and only minimally affecting their natural gloss. Surprisingly, the compositions of the present invention reduced the weight loss of coated peppers by ˜50% as compared to non-coated peppers, thus doubling the shelf life of coated peppers versus the non-coated ones. Although the natural gloss of the peppers was typically reduced by about 25% upon coating with the composition of the present invention, brushing of the peppers restored their natural shine, while maintaining the weight loss of the coated peppers significantly lower than the weight loss of the uncoated peppers.
The compositions of the present invention are highly advantageous as they restore the natural gloss of the post-harvest fruits and vegetables as well as significantly reduce their water loss and preserve their pleasing taste. It should be appreciated that by virtue of the specific combination of the ingredients of the compositions of the present invention, the three effects, i.e., restoration of the natural gloss, reduction of water loss, and preservation of the taste of the post-harvest fruits and vegetables, are achieved. Known coating compositions, although capable of restoring the natural gloss of post-harvest fruits and vegetables, often harm the pleasing taste of these fruits and vegetables. Thus, the compositions of the present invention provide, for the first time, means for coating post-harvest fruits and vegetables which restores their natural gloss, reduces their water loss, and preserves their pleasing taste, thereby extending their shelf-life without compromising their appealing appearance.
According to a first aspect, the present invention provides a composition for coating edible plant matter having a natural gloss, the composition comprising an edible wax having a melting temperature below 70° C., a hydrocolloid polymer, a fatty acid, an emulsifier and water, wherein the edible wax is present in an amount greater than 10% (w/w) and preferably equal or greater than 15% (w/w) of the total weight of the wet coating composition, wherein the amount of wax in the composition reduces the weight loss of the plant due to water evaporation while maintaining the pleasing taste and natural gloss of the plant matter as compared to a plant matter coated with the same composition with edible wax in an amount equal or lower than 10% or with an edible wax having a melting temperatures higher than 70° C. According to certain embodiments, the edible wax should constitute about 10 to 25% (w/w) of the weight of the wet coating composition and preferably between 15 and 25% (w/w) of the weight of the wet coating composition. Accordingly, after drying the coating on the surface of the edible plant, the edible wax will constitute between 55-80% (w/w) and preferably between 60-80% (w/w) of the dried composition. It is to be emphasized that after coating the plant matter, the wax-hydrocolloid coating is left to dry, preferably at room temperature. Preferably the drying of the coating results with a hydrocolloid-wax coating having low water activity. Typically the dried coating composition on the surface of the plant matter comprises up to 10% of water, preferably up to 5% of water, preferably, up to 3% of water and more preferably, up to 2% of water. Each possibility represents a separate embodiment of the invention.
According to some embodiments, the edible wax is having the melting temperature of up to 75° C. According to some embodiments, the edible wax is having the melting temperature of between 45 and 75° C. According to some embodiments, the edible wax is having the melting temperature of up to 70° C. According to some embodiments, the edible wax is having the melting temperature of between 50 and 70° C. According to some embodiments, the edible wax is selected from animal wax, insect wax, vegetable wax and mixtures thereof; each possibility represents a separate embodiment of the invention. According to some embodiments, the edible wax is an animal wax or an insect wax. In some preferred embodiments, the animal or insect wax is beeswax. In yet some other embodiments, the edible wax is a vegetable wax. Non limiting examples of vegetable waxes include candelilla wax, Japan wax, soy wax, bayberry wax, castor wax and mixtures thereof. Each possibility represents a separate embodiment of the present invention. According to still further embodiments, the edible wax is selected from mineral waxes, such as, but not limited to montan wax. According to yet a further embodiment, the edible wax is selected from petroleum waxes. According to some embodiments, petroleum waxes are selected from the group consisting of microcrystalline wax, paraffin wax, and mixtures thereof. Each possibility represents a separate embodiment of the present invention.
According to some embodiments, the amount of edible wax having a melting temperature below 75° C. and preferably below 70° C. in the composition is sufficient to provide the following parameters to an postharvest edible plant matter coated with the composition:
1. reduction of water loss;
2. preservation of the pleasing taste with no off-flavors; and
3. restoration of the natural gloss,
as compared to an edible plant matter coated with a composition containing less than 10% (w/w) of wax in the wet composition or an edible plant matter coated with a composition containing same amount of wax, wherein the wax is having a melting point above 75° C.
The hydrocolloid polymer is typically present in an amount lower than 2% (w/w), preferably lower than 1% of the total weight of the wet coating composition. According to some embodiments, the weight percent of the hydrocolloid polymer in the composition is equal or lower than 0.5% (w/w), although the appropriate percentage of the hydrocolloid polymer will be determined for the actual hydrocolloid polymer used, as is well known to one of skill in the art. After drying of the hydrocolloid-high wax composition, the hydrocolloid polymer weight percentage will correspondingly rise and, typically, will comprise a weight percent of 0.1 to 10% of the dry composition. Importantly, the hydrocolloid used in compositions and methods of the invention may influence the viscosity of the composition however it does not gellify the wet composition. Thus, according to some embodiments, the hydrocolloid polymer used may be selected from a non-gelling hydrocolloid polymer, a gelling hydrocolloid added to the composition in an amount lower than the amount sufficient for gellifing the composition or a gelling hydrocolloid added to the composition in the absence of a sufficient amount of cross-linking agents (such as for example potassium ions, or calcium ions) capable of causing the gellification of the composition.
In some embodiments, the hydrocolloid is a non-gelling hydrocolloid. In some embodiments, the non-gelling hydrocolloid is selected from the group consisting of locust bean gum (LBG), guar gum, xanthan gum and lambda-carrageenan. Each possibility represents a separate embodiment of the present invention. In some embodiments, the hydrocolloid is a gelling hydrocolloid used in an amount lower than the amount necessary for gelling the compositions of the present invention. Non-limiting examples of hydrocolloid suitable for use in the compositions of the present invention include: alginate, carrageenan, agar, agarose, arabinoxylan, carboxymethylcellulose, cellulose, curdlan, gelatin, gellan, β-glucan, pectin, starch, gum arabic, gum tragacanth, tamarind gum, fenugreek gum, cassia gum, tara gum. Each possibility represents a separate embodiment of the present invention. In an exemplary embodiment, the hydrocolloid is locust bean gum (LBG).
Without being limited by any specific theory or mechanism of action, the introduction of the hydrocolloid polymer into the wax composition altered the ordered structure of the wax in the composition after it has been dried on the surface of the plant matter, permitting better gas exchange with the atmosphere and thus resulting with a decrease in the production of off-flavor. As a result of this non-uniform or “imperfect” coating, the respiration of the coated plant matter is less disturbed and lower levels (relative to commercial coatings based on wax) of ethanol and acetaldehyde accumulate in the coated plant matter.
According to further embodiments, the fatty acid is typically present in the wet composition in the amount ranging from about 0.2 to about 10% (w/w). The emulsifier is typically present in the wet composition in an amount ranging from about 0.1 to 15% (w/w), preferably from about 0.1 to 10% (w/w), and more preferably from about 0.1 to 5% (w/w), and even more preferably from about 0.1 to 3% (w/w). According to certain embodiments, the emulsifier amount is lower than 2% (w/w) of the total weight of the wet coating composition.
In some embodiments, the fatty acid comprises an aliphatic chain of between 12 and 24 carbon atoms. In some embodiments, the aliphatic chain is saturated. In some embodiments, the aliphatic chain is un-saturated. Non limiting examples of fatty acids suitable for the coating composition of the present invention include oleic acid, stearic acid, palmitic acid, lauric acid, myristic acid, behenic acid, and isostearic acid. Each possibility represents a separate embodiment of the present invention. In an exemplary embodiment, the fatty acid is oleic acid.
In certain embodiment, the emulsifier is an edible emulsifier selected from non-ionic emulsifier, anionic emulsifier, and mixtures thereof. Each possibility represents a separate embodiment of the present invention. In some embodiments, the emulsifier enables to composition to be in a liquid form at room temperature. According to some embodiments, the emulsifier facilitates the solubility of the wax in the composition. According to some embodiments, the emulsifier served as a pH modifier of the composition. Non limiting examples of suitable emulsifiers include morpholine, ammonia, lecithin, ethylene glycol monostearate, ammonium lauryl sulfate, sodium steroyl-2-lactylate, potassium oleate, propylene glycol monostearate, sodium alkyl sulfate, polyglycol. Each possibility represents a separate embodiment of the present invention. In an exemplary embodiment, the emulsifier is morpholine.
In additional embodiments, the composition may further comprise a resin. In some embodiments, the resin may be selected from the group consisting of shellac, copal, damar, elemi and mixtures thereof. Each possibility represents a separate embodiment of the present invention. According to some embodiments, when the wax is a vegetable wax, an animal or insect derived resin (such as shellac) is added to the composition, preferably at a weight ratio of up to 5% of the total weight of the wet composition.
The composition of the present invention may further contain additional substances selected from the group consisting of antifoaming agents, preservative agents, adhesive agents, cross-linking agents, plasticizers, and surface-tension reducing agents. Each possibility represents a separate embodiment of the present invention. Exemplary additional substances include, but are not limited to polydimethylsiloxane (PDMS), potassium carbonate, sodium bisulfite, sodium benzoate, sodium propionate, calcium propionate, benzoic acid, potassium sorbate, polyethylene glycol, glycerol, propylene glycol, sorbitol, mannitol, high laurate canola oil (Laurical™), Astral R and HUMKOTE®. Each possibility represents a separate embodiment of the present invention.
According to some embodiments, the composition for coating edible plant matter comprises: from about 10% to about 25% (w/w) of edible wax, up to about 2% (w/w) of a hydrocolloid polymer, from about 0.5 to about 5% (w/w) of the fatty acid, and from about 0.3 to about 5% (w/w) of the emulsifier in the wet composition. According to some embodiments, the edible wax is beeswax. According to some embodiments, the hydrocolloid polymer is locust bean gum. According to some embodiment, the fatty acid is oleic acid. According to some embodiments the emulsifier is morpholine.
According to some embodiments, the composition for coating edible plant matter comprises: from about 10% to about 25% (w/w) of edible wax, up to about 1% (w/w) of a hydrocolloid polymer, from about 0.5 to about 5% (w/w) of the fatty acid, and from about 0.3 to about 5% (w/w) of the emulsifier in the wet composition. According to some embodiments, the edible wax is beeswax. According to some embodiments, the hydrocolloid polymer is locust bean gum. According to some embodiment, the fatty acid is oleic acid. According to some embodiments the emulsifier is morpholine.
According to some embodiments, the composition for coating edible plant matter comprises: about 10%-25% (w/w) of beeswax; up to about 1% (w/w) of hydrocolloid; about 0.2%-10% (w/w) of fatty acid; about 0.1%-15% (w/w) of emulsifier; and about 49%-89% water, of the total weight of the composition.
In one embodiment, the composition is applied to the edible plant matter postharvest.
In another embodiment, the edible plant matter comprises a fruit or a vegetable having naturally gloss appearance. In some embodiments, the edible plant matter comprises a fruit or a vegetable selected from the group consisting of peppers, eggplants cherries, berries plums and persimmons. Each possibility represents a separate embodiment of the present invention. In some embodiments, the peppers are selected from the group consisting of bell peppers, sweet peppers, chili peppers, and paprika peppers. Each possibility represents a separate embodiment of the present invention. In an exemplary embodiment, the plant matter is a bell pepper. In another embodiment, the edible plant matter comprises a fruit or a vegetable having small or limited water reservoir capacity. In particular embodiments, the edible plant matter comprises a fruit or a vegetable having from about 75% to about 95% (w/w) water content.
According to another aspect the present invention provides a method for reducing the weight loss and/or preserving the natural gloss of a post-harvest edible plant matter comprising step of applying to the surface of the plant matter a composition comprising: an edible wax having a melting temperature lower than 70° C.; a hydrocolloid polymer; a fatty acid; an emulsifier; and water, thereby coating the edible plant matter, wherein the edible wax is present in a weight percent ranging from 10% to 25% of the wet composition and from 50% to 85% (w/w) of the dried composition.
According to some embodiments, the composition is applied to the surface of the plant matter by rubbing the composition onto the surface of the plant, possibly by using of rubber gloves, dipping or immersing the edible plant matter in the composition, spraying the composition onto the edible plant matter, pouring the composition onto the plant matter, possibly when the plant matter is moving on a conveyor belt. Each possibility represents a separate embodiment of the present invention.
According to some embodiments, the application of the composition of the present invention to the surface of the plant matter is performed at room temperature (25° C.±10° C.). According to some embodiments, the composition is applied to the surface of the plant matter and/or to the stem of the plant matter when the temperature of the composition is between 35° C. to 70° C., preferably at a temperature of between 35° C. to 50° C. After applying the hydrocolloid-wax composition to the surface of the plant matter, the coating is left to dry on the surface of the plant matter, preferably at room temperature.
According to some embodiments, the method of the invention further comprises the step of brushing the coated edible plant matter. The brushing of the coated plant matter restores the glossy appearance of the plant matter to at least 80% of the natural gloss of uncoated plant matter, preferably to at least 85% of the natural gloss of the uncoated plant matter and most preferably to about 90% of the natural gloss of the uncoated plant.
Polishing or brushing the coating decreased its thickness and induced the redistribution of the wax on the surface of the plant matter which increased the gloss values of the coated plant matter. Polishing of a plant matter coated with a hydrocolloid-wax composition wherein the wax had a melting temperature below 70° C. (e.g. beeswax) resulted in a glossier appearance as compared to a plant matter coated with a hydrocolloid-wax composition wherein the wax has a melting temperature above 70° C. (e.g. carnauba wax). Without being limited by any theory or mechanism of action, the glossier appearance may result from the greater redistribution of the wax due to its relative softness.
According to some embodiments, the coating thickness prior to brushing is between 20 and 50 μm thick. According to some embodiments, the coating thickness is reduced by up to 50% upon brushing. According to some embodiments, the brushing of the coated plant matter is performed using a brush comprising natural fibers such as horse hair fibers. According to some embodiments, the brushing of the coated plant matter is performed using a brush comprising synthetic fibers such as nylon or polyethylene fibers. According to some embodiments the brush comprises horse hair fibers. According to some embodiments, the coated plant is brushed for up to 20 minutes, preferably between 1-10 minutes, at a brushing speed of about 100 to 300 rpm.
According to some embodiments, the method of the invention provides the extension of shelf life of edible plant matter by reducing the extent of weight loss during storage. According to some embodiments, the weight loss of a plant matter coated with the composition of the invention is reduced by at least 20%, preferably by at least 30%; preferably by at least 40%; and most preferably by about 50% as compared to an uncoated plant matter under same storage conditions. According to some embodiments, the method of the present invention provides the extension of the shelf life of the edible plant matter for between several days to several weeks beyond the shelf life of uncoated edible plant matter under the same storage conditions. According to some embodiments, the shelf life of an edible plant matter coated with the formulation of the invention is doubled as compared to the shelf life of an uncoated plant matter under the same storage conditions.
The methods of the present invention are particularly advantageous for the coating of edible plant matter comprising fruits or vegetables having small water reservoir capacity and/or to fruits or vegetables having a natural glossy appearance such as for example peppers, eggplants and persimmons. According to some currently preferred embodiments, the methods of the present invention suitable for coating peppers.
According to some additional preferred embodiments, the present invention provides a method for reducing the weight loss and/or preserving the natural gloss of a post-harvest edible plant matter comprising step of applying to the surface of the plant matter a composition comprising: beeswax; present in a weight percent ranging from 10% to 25% of the wet composition and from 50% to 85% (w/w) of the dried composition, a hydrocolloid polymer; a fatty acid and an emulsifier. According to yet additional preferred embodiments, the present invention provides a method for reducing the weight loss and/or preserving the natural gloss of a post-harvest pepper (such as a bell-pepper) comprising the step of applying to the surface of the pepper a composition comprising: beeswax; present in a weight percent ranging from 10% to 25% of the wet composition and from 50% to 85% (w/w) of the dried composition, a hydrocolloid polymer; a fatty acid and an emulsifier.
In another aspect, the invention provides a method for preparation of the hydrocolloid-high wax compositions useful for the coating of a plant matter, particularly fruit or vegetable having limited water reservoir capacity and high natural gloss, the method comprising the steps of: a) adding a hydrocolloid to preheated water having a temperature in the range from about 55° C. to about 95° C., more preferably from about 75° C. to about 85° C.; b) adding a fatty acid and an emulsifier to the mixture obtained in step a; c) adding molten wax to the mixture obtained in step (b).
Further embodiments and the full scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.