Field of the invention

The present invention relates to the field of agricultural science and technology, especially to a method for synthesizing carboxymethylcellulose-based composite film for prolonging shelf life.

Background of the invention

Food, fruit, and vegetable are essential for human life and they are also a significant source of income at the household and national levels. Thailand is one of the countries which has high volume of agricultural exports, processed foods, and unprocessed foods. These kinds of food, whether it is fresh or processed food, fruit, and vegetable, could spoil easily due to their sensitivity to the environment, temperature, air permeability, humidity, pathogenesis, and damage caused by animals and insects, leading to spoilage, denaturation, or quality change easily and quickly. Therefore, it requires a procedure for controlling or maintaining food quality as long as possible to prolong shelf life and keep the food fresh when delivering it to consumers. The procedure for controlling or maintaining food quality could be done by many different methods, e.g. containing food in a fully-closed package; using low temperature, pressure, or gas for the preservation; or having food processing operation to maintain nutritional and physical qualities. Furthermore, the efficiency of food preservation could be achieved by proper preparation, pleasant property, and freshness of food, not being damaged by such physical force as fracture, bruise, and crash and by feeding insects, which directly cause food spoilage.

Food preservation is a key to food products after purchase, and there has been a continuous research and development activity that seeks the right preservation method, with pleasant quality and physical property, for different types of food. Apart from the above-mentioned examples, food preservation could also be done by the following methods: cleaning, compound soaking, cutting, processing, and compound coating, which suit for different kinds of food product. One of the most interesting methods that could surprisingly maintain physical property of food products is film coating or composite coating which is found in the following prior art:

Thai patent application no. 9901002530, invention titled “Film coating and polyvinyl alcohol-based mixture for film coating”, illustrates a dried mixture for film coating in medicinal tablet, supplementary food, food, confectionery, agricultural tablet, and those of similarity comprising polyvinyl alcohol, plasticizer, pigment or coloring substance, and lecithin; a method for coating substrate by aqueous dispersion; and a method for drying the coating film;

Thai patent application no. 0801000023, invention titled “Non-synthetic edible cellulose- based composite for producing fresh egg coating materials”, illustrates a non-synthetic edible cellulose-based composite comprising cellulose, plasticizer, hydrophobic reactant, solvent, with or without active ingredients, that are processed to obtain a transparent gel-like solution with medium viscosity. This solution is suitable for coating fresh egg or it could be a substitute for oil/wax-based egg coating materials, which efficiently preserve egg quality.

Thai patent application no. 1103000658, invention titled “Method for producing polymer film substrate from polyethylene and calcium carbonate”, illustrates a method for producing film substrate by blending particulate filler and calcium carbonate in a screw extruder with speed and temperature control, pelletizing substance by a pelletizer, dehumidifying plastic pellets in a dryer, and blowing dehumidified plastic pellets into film with a blown film extruder under a control temperature to obtain desirable mechanical properties and size. By using this method, we could obtain a polymer film with pleasant gas permeability which could be used as a packaging material, under modified atmosphere, for fruit and vegetable to prolong shelf life.

Thai patent application no. 1701001215, invention titled “Edible coating solution from chitosan and carboxymethylcellulose for prolonging the shelf life of modified food, vegetable, and fruit”, illustrates a formula of edible coating solution for prolonging the shelf life of fresh-cut food, vegetable, and fruit comprising chitosan, carboxymethylcellulose, and solvent. In addition, the edible coating solution according to this invention further comprises any one or more of edible plasticizer, edible disinfectant of foodbome pathogen, edible antioxidant, edible color additive, and edible flavor.

As mentioned above, there are inventions related to coating method, method for producing coating material or film, and composition of coating material or film. Each invention has different method and composition that suits for different kinds of food products. The inventor has developed a method for synthesizing carboxymethylcellulose-based composite film for prolonging shelf life in order to obtain a suitable coating material for prolonging shelf life of products, wherein the aforementioned coating material causes no harm to consumer’s health and environmental pollution. Summary of the invention

The method for synthesizing carboxymethylcellulose-based composite film for prolonging shelf life is a film synthesizing method comprising steps of modifying crystallizing agent, preparing carboxymethylcellulose solution, and performing film coating to obtain a film for coating food, vegetable, fruit, and tree branch, which causes no harm to consumer’s health and it is eco-friendly.

The objective of the present invention is to provide an alternative for prolonging shelf life of food, vegetable, fruit, and tree branch by using a carboxymethylcellulose-based composite film which is suitable for prolonging shelf life of food, vegetable, fruit, and tree branch because it could help control and maintain quality and physical properties, such as, delaying internal fibre fracture from dehydration, reducing ethylene release, reducing mold growth on peels, maintaining natural color, maintaining crispness, delaying spoilage, delaying germination, which are important for product value during the storage, distribution, and shipment to consumers.

Detailed description of the invention

The method for synthesizing carboxymethylcellulose-based composite film is effective for coating a product with plain, porous, and rough surface because it allows effective coating throughout the surface. The reason is that carboxymethylcellulose is hydrocolloid, which is a hydrophilic polymer and a carbohydrate of cellulose derivative. This type of hydrocolloid is modified or adjusted for its properties of cellulose, which is a composition of plant cell wall allowing the substitution of methyl group and carboxymethyl group. Its characteristic is solid, white, odorless, tasteless, harmless, eco-friendly, water-soluble, and it could be a thickening agent for adhesion and maintenance, suitable for using as an edible film or coating material. Furthermore, it is a renewable material which is biocompatible and biodegradable.

The carboxymethylcellulose-based composite film is further provided with modified calcium carbonate because calcium carbonate has a property of ultrafine grinding, chemical stability, non-toxicity, white color, and oil absorption. The mixture will help seal porous surface which reduce the internal/extemal air exchange effectively. Calcium carbonate could be found generally in nature and in animals like shells and bones. It is mostly found in nature in the form of limestone and calcite or calspar. A substitute mineral for calcium carbonate is, such as, magnesium oxide and titanium dioxide. The method for synthesizing carboxymethylcellulose-based composite film for prolonging shelf life comprises steps as follows:

Step for the preparation of modifying crystallizing agent with fatty acid comprises:

Adding 1 to 10 grams of fatty acid in 168.5 to 200 milliliters of base solution while mixing and heating at the temperature of 75 to 120 degrees Celsius, wherein fatty acid could be selected from any one or more of butyric acid, lauric acid, palmitic acid, or stearic acid or a combination thereof, wherein the suitable fatty acid is stearic acid, and base solution could be selected from any one or more of sodium bicarbonate, magnesium hydroxide or a combination thereof, wherein the suitable base solution is sodium hydroxide;

Adding 20 to 50 grams of crystallizing agent and 5 to 20 milliliters of distilled water, then mixing homogeneously, wherein the crystallizing agent could be selected from any one or more of calcium carbonate, magnesium oxide, or titanium dioxide or a combination thereof, wherein the suitable crystallizing agent is calcium carbonate which helps enhance crystallinity of coating material on food, vegetable, fruit, and tree branch to reduce carbon dioxide and oxygen permeability for prolonging shelf life;

Filtering by a filtration assembly and heating at the temperature of 50 to 70 degrees Celsius for 24 hours. Step of preparing carboxymethylcellulose solution and performing film coating comprises:

Dissolving 1.5 to 5 grams of carboxymethylcellulose in 98.5 to 150 milliliters of distilled water, adding 1 to 5 milliliters of plasticizer, and adding 20 to 30 grams of modified crystallizing agent, mixing homogeneously, wherein plasticizer could be selected from any one ore more of glycerol, sorbitol, sucrose, xylose, glutaraldehyde, or polyethylene glycol or a combination thereof, wherein the suitable plasticizer is polyethylene glycol-400;

Adjusting an acid-base balance of solution by dropping base solution until an acid-base balance turns neutral;

Heating at the temperature of 80 to 100 degrees Celsius for 30 minutes; Performing film coating, wherein the preparation of film coating on the surface of food, vegetable, fruit, and tree branch will spread solid or liquid particles throughout the surface to prolong shelf life effectively, wherein the coating could be selected from:

Spray tunneling which is a coating method using a spray tunneling system by providing an electrostatic magnetic field inside the tunnel at the side and controlling air pressure to control the coating direction sprayed by electric charge and air pressure to a predetermined product surface directly; thus, this method allows effective spraying, not exceeding specified area, wherein this method sprays coating on the product surface with the least thickness;

Spray coating which is a coating method emphasizing thickness of film layer on the coated product surface by spray coating throughout the product surface and drying, wherein this method could perform spray coating for multi layers as desired;

Cast coating which is a coating method suitable for forming amorphous film and not emphasizing thickness of film layer by pouring coating on the product surface and drying;

Paint coating which is a coating method using a paint coating device painting on the product surface and drying;

Fluidized bed coating which is a spray coating method having a principle to spray coating material in small droplets to make it adhere on particle surface while suspending in the air, wherein this method allows thorough and consistent particle surface adhesion as the aforementioned method is a cooperation of coating and drying simultaneously;

Dip coating which is an easy, convenient, and fast method that could be done by dipping in coating solution for a certain period of time and drying, wherein each method is different in terms of the consistency, thickness of film layers after coating, convenience and speed, amount of coated product for each time, coating cost, and continuity of coating.

After finishing coating process, it is further provided with a step of investigating film coating thickness by the measurement of film surface, wherein the measurement method could be selected from micrometer, ultrasonic, gravimetric, or coating thickness gauge.

The information from the test of using carboxymethylcellulose-based composite film for prolonging shelf life is as follows:

According to the test result table above, it could illustrate the efficiency after using carboxymethylcellulose-based composite film for prolonging shelf life by coating on each type of food, vegetable, fruit, and branch. The different physiology affects the efficiency of coating solution differently as follows:

Fruit on Peel: Coating could help reduce transpiration, ethylene gas release, ripening from other side effects, mold growth on peels, and also enhance peel thickness.

Fresh-cut Fruit: Coating could help delay internal fiber fracture from dehydration (firmness texture), maintain natural color, and delay braise. Vegetable: Coating could help maintain crispness by delaying dehydration, maintaining odor (pungency), preventing internal structure of fruit from being soft and pulpy, maintaining firm external structure of fruit, delaying calyx fall, delaying germination, delaying spoilage for fresh- cut portion, delaying mold growth on peels, and delaying loss of starch content in cassava (delaying the conversion of starch to glucose).

Tree Branch: Coating could help reduce germination rate and dehydration in tree branch and prolong life span of tree branch for cuttings.

Any modifications are clearly comprehensible and could be done by a person skilled in the art. Thus, it is under a scope and intention of the present invention as shown in the attached claims. Best mode of the invention

As mentioned in detailed description of the invention.