In our impression, most of the packaging materials are inedible, even natural sources of paper materials, but also because of the late bleaching, plus a variety of additives difficult to eat directly, and extremely poor taste. The use of edible films, however, dates back to the 12th century in our country, when our ancestors used waxing to extend the shelf life of citrus as early as the 12th century. Edible sausage casings and glutinous rice paper are also the first typical edible packaging used in China.
Can't believe it, but your favorite sausage casings are typically edible membranes.
Edible sausage casings
According to the scientific definition, edible membranes are composite membranes formed by edible materials, which are mainly composed of natural macromolecules such as lipids, proteins and polysaccharides. Film-forming materials can be classified according to their functional properties: main agents (polysaccharides, proteins), hydrophobic agents (waxes, fatty acids, etc.) and plasticizers (polyols and lipids).
Compared to synthetic packaging materials, edible film is biodegradable and free of contamination. It can also be used as a carrier for food flavors, nutritional fortification, antioxidants, and anti-microbial agents.
Currently, edible coating films and edible packaging films in China are mainly used in foods such as fruits, vegetables, candies, nuts and pastries.
According to the classification of raw materials, edible films can be broadly classified into four categories: polysaccharide-based edible films, protein-based edible films, lipid-based edible films and composite edible films. The following is an introduction of each type of film.
Polysaccharide edible film
Polysaccharide-based edible films are made from starch, modified starch, edible gum, and fiber derivatives as the main raw materials.
Due to the special long-chain helical molecular structure of polysaccharides, they are chemically stable and suitable for long-term storage and various storage environments, but they are hydrophilic polymers and generally have little moisture resistance.
1 . Cellulose edible film
In recent years, the research and development of modified cellulose edible packaging films has received much attention worldwide. The production of easily degradable composite plant fiber disposable food and food packaging materials developed in Xinjiang, China, has been commercialized. Liu Linwei et al. used methyl cellulose and carboxymethyl cellulose as raw materials and stearic acid, soft stearic acid, beeswax and agar as plasticizers and reinforcing agents to produce translucent, soft, smooth and melt-in-the-mouth packaging films with high tensile strength, low moisture permeability and air permeability.
The main factors influencing the film formation of wheat gluten protein and the optimal process conditions were determined by single factor tests and orthogonal tests, and the film resistance was further improved by adding stearic acid and paraffin wax. The results showed that the membrane with paraffin was about 10% more moisture resistant than the membrane with stearic acid.
2. Starchy edible film
Starch-based edible films are made from starch as the main raw material. The raw materials for starch-based edible films include corn, wheat, sweet potato, potato and konjac starch, etc. The adhesives used are mostly natural non-toxic vegetable or animal gums, such as gelatin, agar and natural resin gums.
In the late 1960s, edible membranes were extensively studied abroad. The cereal films developed at Clemson University in South Carolina, USA, are made from corn, soybeans and wheat and are used as paper-like films for packaging food products such as sausages and are available for consumption. a preliminary discussion of the application of starch films was made by Maria A Garcia et al.
The starch was modified with dilute alkali solution and glycerol was added as a plasticizer. Fresh strawberries were treated with this prepared coating solution and stored at 0°C and 84.8% relative humidity. The results showed that the treated strawberries outperformed the control group in terms of water loss rate, hardness and spoilage rate.
3. Animal and plant gum edible film
Japan has been a world leader in the development and application of animal and vegetable gum edible films. These edible films are made from animal gums (such as bone gum and shellac) and plant gums (such as glucomannan, keratan, pectin, sodium alginate, etc.) as substrates and glycerol, polyol, sorbate, etc. as plasticizers.
It has good transparency, high strength, good printability, heat sealability, gas barrier and water and moisture resistance, and has been used in the packaging of condiments, sweeteners, soups and fats and oils, etc. It can also be used in the wrapping of frozen foods, candy and dried fruit to prevent adhesion.
The collagen film developed by Natick, USA, is made of animal protein collagen. The film has high strength, water and air resistance, and is used for packaging meat products to preserve their flavor.
Polysaccharide-based biofilms have a wide range of applications in medicine, such as membranes made of regenerated cellulose for hemodialysis, plasma separation and virus removal; membranes made of titin can be used as artificial skin or surgical thread for wound healing or hemostasis, with the advantage that titin can be degraded and absorbed by the body and can promote wound healing.
4. Chitin and chitosan-based edible membranes
Chitin and chitosan have good film-forming and biodegradable properties and are very suitable for the manufacture of edible packaging materials. Caner et al. investigated the effects of different types of acids (acetic acid, formic acid, lactic acid, propionic acid) on the properties of chitosan films and found that lactic acid chitosan films have good oxygen barrier, moisture barrier and elongation properties.
Brandenburg A H et al. added chitin and chitosan to an aqueous solution of starch, mixed the film, and treated it with alkali after drying to produce a composite film of starch + chitin + chitosan, which is oil resistant, insoluble in water, and has high tensile strength and can be used for packaging solid, semi-solid or liquid foods.
Kim Y J et al. used corn starch as the base material, added chitin and chitosan respectively, and processed with certain amount of plasticizer and viscosity enhancer to form composite packaging paper, which is mainly characterized by high tensile strength and elongation, and strong water resistance, even when immersed in boiling water for l0 min, its performance remains little changed.
Protein-based edible film
Protein-based edible films are made from animal and plant isolates such as whey protein, gluten and maize soluble proteins.
In the process of film formation, the protein film mainly relies on the action of disulfide bond (S-S), firstly, the S-S bond is reductively cleaved to sulfhydryl group, which is diffused in the solvent to lower the peptide molecules, and then the diffused protein molecules are oxidized in the air to re-form the S-S bond and form the film structure.
Common protein-based edible films include soybean isolate, whey protein, wheat gluten and corn soluble protein films.
1 . Soybean isolate protein membrane
The membranes are made from soy protein isolate and glycerol, and are made edible under both acidic and alkaline conditions.
Soybean isolate membranes have good mechanical and moisture resistance properties. Deng Yangwu et al. studied the film formation properties of soybean isolate protein and concluded that edible packaging films with good tensile strength and elongation could be produced at a ratio of 2.5:1 of soybean isolate protein to glycerol, pH 7 of the film solution, and 90°C of the film preparation temperature.
2. Wheat gluten protein film
Wheat gluten is mainly composed of wheat gluten and wheat alcohol protein, of which 30%-40% is wheat gluten and 40%-50% is wheat alcohol protein. Due to the elasticity of wheat gluten and the elongation of wheat alcohol protein, they can form a network structure with water and thus have unique physical properties such as excellent viscoelasticity, elongation, water absorption, lipid-absorbing emulsification and film-forming properties.
The effects of lipids on properties such as mechanical and permeability of wheat protein membranes were investigated by Lu-Li Meng et al. The results showed that the hydrophobic properties of lipids could effectively prevent water migration, and their complexation with proteins could improve the moisture barrier property of protein membranes. In addition, the mechanical properties and water solubility of wheat protein membranes varied depending on the type and amount of lipids.
3. Corn alcohol soluble protein film
Maize alcohol soluble protein has good hydrophobic properties that other protein films do not have, easy to form a film, its alcohol-water solution in the formation of irregular nematic structure, solvent evaporation can be made into a transparent, glossy film, with moisture, oxygen barrier, anti-UV, fragrance, oil and anti-static properties, and a certain inhibitory effect on bacteria, can extend the shelf life of food.
Yan Jingkun et al. showed that the tensile strength and elongation of protein films decreased with the increase of refrigeration and freezing time; the mechanical properties of protein films were better under refrigeration conditions than under freezing conditions.
4. Peanut isolate protein membrane
Peanut protein isolate has good film-forming properties. Peanut isolate protein membrane has a certain tensile strength, and also has a certain ability to prevent water vapor migration, which is a promising edible membrane.
Jangchud studied the effects of glycerol, sorbitol, polyethylene glycol, and malondiol on peanut protein membranes. The results showed that glycerol was the most effective plasticizer, and the mass ratio of glycerol to protein was 0.67~1.67g/g, which did not affect the water permeability and oxygen permeability, but could significantly increase the elongation at break.
5. Silk Silk Protein Film
Ruijuan Xie and Mingzhong Li used epoxy resin as the cross-linking agent to prepare silk glue protein film with certain mechanical properties, which improved the physical properties.
Chen et al. prepared nano-TiO2-modified regenerated silk sericin protein films by sol-gel method. The mechanical strength of the silk protein film was improved and the dissolution rate in water was decreased.
6. Sunflower protein film
Orliac investigated the effects of glycerol, ethylene glycol, diethylene glycol, triethylene glycol and propylene glycol on the properties of thermally molded sunflower protein films and concluded that triethylene glycol and glycerol are the most suitable plasticizers for sunflower proteins.
7. Myogenin membrane
Natick Research Institute in the United States uses animal protein collagen edible packaging film to package meat, which is characterized by high strength, good water resistance and water vapor barrier, collagen film can be melted when thawed, but also edible, harmless to humans. At the same time, it also solves the problem of marine pollution caused by food packaging plastics.
Composite edible film
By combining polysaccharides, proteins and fatty acids in different ratios to make edible films, the mechanical strength, light transmission, air permeability and water retention of the films can be improved by changing the types and contents of polysaccharides and proteins in the composite films to meet the needs of different food packaging.
Li Mengqin studied the effect of calcium chloride, a cross-linking agent, on the performance of wheat gluten composite film, and obtained that the optimum addition of calcium chloride was 0.67%, and the tensile strength of the composite film made under this condition increased by 13.4% and the water vapor transmission coefficient decreased by 7.3%, and the application of calcium chloride cross-linking could significantly increase the strength of edible film and improve the mechanical properties of the composite film.
Genndios used a mixture of soybean isolate, corn alcohol soluble protein and wheat gluten protein to make the membrane. The results showed that the water resistance of the membrane was significantly stronger than that of wheat gluten protein alone when the ratio of wheat gluten to corn alcohol soluble protein was 4:1.
Mau-Chang Chen's study of methyl cellulose and stearic acid composite membranes showed that increasing the volume fraction of stearic acid fraction to 22% significantly reduced the methyl fibers, and further increasing the stearic acid fraction content would increase the water vapor transmission coefficient of the membrane.
