1.1.1. Introduction:
The term "active packaging" was first applied by Labuza in 1987 and can be defined as packaging that performs some desirable function other than actual packaging products [1].
The intent is to enhance the shelf life of food while preserving nutritional quality and ensuring their safety, which shows more unilities than simple wrapper. Because of advancements in packaging, material science, biotechnology and new consumer needs, active packaging systems are often combined with controlled atmosphere packaging (CAP) or modified atmospheric packaging (MAP). Usually, active packaging is used to prevent moisture loss during food storage and transportation. The present day, they are being used widely to ensure the quality of food, inhibit the growth of bacteria organisms that cause food spoilage, increase the shelf life of products, and limit contamination from surrounding environment [2]. This technology is based on the removability of undesired compounds from foods or its environment such as: moisture, ethylene, oxygen, etc. The complex structure of foods can be modified by avitivity of packaging, active substances that are added, specifically. These substances are able to control release rates, absorption rates, diffusion rates, etc. Normally, active substances are antimicrobial compounds, antioxidants, carbon dioxide, flavors, ethylene, or ethanol depending on particular food [3].
Most of the food consumed come directly from nature. In addition, the food is being able to be used right after harvesting from the farm in order to reach the hands of consumers, through a time - consuming series of handling, storage, and shipping steps, the product begins dehydration, loss of sensory, taste, nutritional value and lead to spoilage. If there is no guarantee of special protection, damage can happen in hours or days, even if this damage is not immediately visible [4].
In most circumstances, the phrases film and coating are used interchangeably to describe how a food's surface is coated with a thin layer of material containing specific ingredients.
The membrane will be a barrier against transpiration, helping to control physiological and biochemical activities that take place inside food, contributing to maintaining the freshness of food products during storage [5].
Food wraps should have the following characteristics [6]:
– Help stabilize the structure and prevent mechanical damage during transportation and handling and display.
– Do not contain harmful or allergic ingredients.
26 – The good adhesion on food surfaces.
– Control the water content of food to maintain the desired moisture content.
– Prevent loss or absorption of flavor, nutritional and character-stabilizing ingredients food sensibility.
– Resist mold and harmful bacteria.
– Maintain or enhance aesthetic and sensory attributes (appearance, taste, etc) of the product.
– Easy to manufacture and cost-effective.
– Environmental friendliness.
1.1.2. Classification:
1.1.2.1. Classification based on functions:
❖ Oxygen scavengers
High levels of oxygen in food packaging can facilitate microbial growth organisms, produce unpleasant odors, change color, and lose nutrients, thereby significantly reducing the shelf life of the food. Therefore, the control of the oxygen level in the food package is important to limit the possibility of spoilage in food. The oxygen absorption system provides an alternative to gas and vacuum packaging while improving the quality and shelf life of the product. Furthermore, they are economical in terms of cost reduction packaging and increase profits. The oxygen scavengers absorber is not suitable for liquid food, because direct contact with the liquid often causes the spillage of substances in the oxygen scavengers. Oxygen scavengers sold in the United States are required to be labeled "Do not eat", for safety and regulatory purposes requested by the Food and Drug Administration. Although packages can be wrapped by secondary packages, this method increases the packaging cost [7].
❖ Carbon dioxide scavengers and emitters
Microorganisms generally inhibited by high carbon dioxide levels because it slows their growth on the surface of meat and poultry and in delaying respiration of fruit and vegetables. Carbon dioxide is more permeable than oxygen, that a reason why it usually applies in food packaging. Most of the carbon dioxide inside the package is normally permeable through the membrane. For packaging which is highly permeable to carbon dioxide, a carbon dioxide emitter system can be needed to slow down respiration and prevent microbial growth. The employment of a dual-function system that includes an oxygen filter as well as a carbon dioxide emitter to extend the shelf life of perishable goods [7].
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❖ Moisture scavengers
Humidity in food packages is very important and necessary to control to prevent the growth of microorganisms and avoid the formation of mist. The lower the water vapor permeability of packaging, the more water accumulation inside the packaging. The formation of water inside the food package often occurs due to the respiration of fresh products, and temperature fluctuations in food packages that have pretty high moisture.
The accumulation of excess water inside the packaging promotes bacteria and mold growth development, leading to reduce quality and reduce shelf life. An effective way to control the accumulation of excess water in a food package with a high vapor barrier must use desiccants such as silica gel, natural clay (for example, montmorillonite), calcium chloride, or other desiccants. Silica gel is the most widely used desiccant because it is non-toxic and non-corrosion [7].
❖ Antibacterial membrane
Humans have been developing strategies to preserve food and prevent the growth of harmful microbes since prehistoric times. Canning, pasteurization, sterilization, freezing, cooling, drying and fermentation are the main methods of food preservation. Nowadays.
When chemical preservatives are combined with these food preservation techniques, there are benefits in preventing microbial contamination after processing and achieving a stronger inhibitory effect on microorganisms. Membranes containing antibacterial substances are of great value in inhibiting the growth of surface microorganisms and prolong shelf life.
A multilayer membrane with antibacterial properties usually consists of four layers, including the outer layer, barrier layer, matrix layer, and control layer. An antibacterial agent is embedded in the background layer. The release of the matrix to the food surface is controlled by the control layer right next to the matrix layer. Among the problems encountered in the antibacterial film is an active ingredient that can partially or completely lose its antibacterial properties when it is introduced into the membrane. Therefore, polymerization or derivatization of active substances prior to their addition to the polymer is necessary to increase compatibility between active agents and polymers [7].
❖Other active packaging
Another active packaging that is expected to develop in the future includes antioxidants releasing films, pigment films, light – modulating absorption systems, anti – fog films and non – stick, air – permeable, film – breathable and film containing insect repellent.
Antioxidant membrane combinations, for example, can be employed to keep fats and oils from oxidizing and becoming rancid. They can also be used to keep smells and other
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flavors developing in foods. Han et al. proved that antioxidant-infused plastic films may effectively prevent oat oxidation [8].
1.1.2.2. Classification based on materials:
❖ Hydrocolloids
Polysaccharides used for membranes include cellulose, starch derivatives, pectin, seaweed extract and CH [9]. The polysaccharide is very hydrophilic, the moisture barrier effect of the polysaccharide coating is negligible. Although the polysaccharide coating may not provide a well vapor barrier, it is reported that these coatings can act as retarding agents for loss of moisture from food products [10].
❖ Lipid membrane
Lipid compounds used as protective coatings include monoglycerides acetylated, natural wax. The most effective lipids are paraffin and beeswax. Main function of lipid coatings is to prevent moisture loss due to their relatively low polarity. The hydrophobic properties of lipids will form thicker and more brittle films, so they must be bound to film – forming agents such as proteins or cellulose derivatives. Lipid membranes are often combined with a substrate such as polysaccharide, to provide mechanical strength [10].
❖ Protein membrane
Membranes from a variety of protein sources, such as corn, milk, soybeans, wheat, and whey, have been used for many years. In the natural state, proteins usually exist in the form of fibrous proteins (insoluble in water) or globular proteins (soluble in water and acid, base or salt solutions). Fibers are formed when fibrous proteins are strongly linked together by hydrogen bonding. Hydrogen bonding, ionic, hydrophobic, and covalent (disulfide) bonds all help globular proteins fold into complex globular shapes. The physicochemical properties of these proteins depend on the number of amino acid group and their position along the polymer chain. The membrane characteristics of several globular proteins have been examined, including wheat gluten, maize zein, soy protein, and whey proteins [10].
1.1.3. Materials to produce active packaging films:
The ingredients used to prepare the membranes are classified into three categories:
hydrocolloid (such as proteins, polysaccharides and alginates), lipids (such as fatty acids, acylglycerols, waxes) and synthetic materials combined [9].
❖ Polysaccharides
Cellulose is made up of D – glucose units that are connected by β – 1,4 glycoside linkages. Treatment of cellulose with alkali, followed by reactions with chloroacetic acid,
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methyl chloride, or propylene oxide to form carboxymethyl cellulose (CMC), methyl cellulose (MC), hydroxypropyl cellulose (HPMC), or hydroxypropyl cellulose (HPC) might enhance its water solubility. MC, HPMC, HPC and CMC film forming have good properties, no odor, tasteless, moderate toughness, oil resistance and water solubility.
Starch is a carbohydrate consisting of many D – glucose units. Most starches contain two types of glucose polymers: a linear polymer called amylose and a branched polymer glucose is called amylopectin. Starch is commonly used in the food industry. It has been used to produce biodegradable membranes that partially or whole polymer because of its low cost and good mechanical properties [10].
High amylose starch, such as maize starch, is a suitable supply of material for manufacturing films, and gelatinized and dried amylose solution can be used to make films.
Amylose and amylopectin make up roughly 25 % and 75 % of normal maize starch, respectively [9].
❖ Lipids
Paraffin wax is derived from the distillate of crude oil and consists of a mixture of solid hydrocarbons by ethylene – catalyzed polymerization. Paraffin wax is allowed to be used on fruits, vegetables, and cheese. Carnauba wax is a secretion from the leaves of palm trees.
Beeswax (white wax) is produced by honey bees. Candelilla is taken from the candle. Wax is used as a gas and moisture barrier (film on fresh fruit) and to improve the appearance of various foods.
If used with a thick wrapper, they must be removed before consuming the product. When used in a thin layer, they are edible. Waxes (notably paraffin, carnauba, candelilla, and beeswax) are good moisture barrier compounds and are edible [9].
❖ Proteins
Gelatin is a protein of animal origin and characterized by its film – forming properties.
Gelatin helps to protect foods from oxidation caused by oxygen and light. It shows the most advantages in low moisture content or oily foods. Gelatin is used to package foods that are low in moisture and contain oils that help protect against oxygen and light [11].
Gelatin films can be formed from 20 – 30 % gelatin, 10 – 30 % plasticizers (glycerol or sorbitol) and 40 – 70 % water, then they will be dried later. In addition, a gelatin film was formed as a coating on the surface to reduce oxidation, moisture [12].
Zein is the most important protein in corn. It is a prolamin protein, which can be dissolved in 70 – 80 % ethanol. Zein is relatively hydrophobic and this hydrophobic property is related to the amount of non – polar amino acids. Zein has good film – forming
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properties and can be used as biodegradable film. The resulting film is brittle and therefore requires the addition of a plasticizer to increased flexibility. Zein film is a relatively good vapor barrier compared to other edible films.