Currently, the demands for food with natural quality, assured safety, minimal processing, extended shelf-life and ready-to-eat concept are booming. Innovation in packaging materials and package design not only ensures transit preservation and effective distribution, but also facilitates communication at the consumer levels. In 21st century the main technological advancement in the area of food packaging is nanotechnology, the science of nano-materials. The word “nano” comes from the Greek for “dwarf”. A nanometer is billionth of a meter (10-9m). Richard Feynman introduced the concept of nanotechnology in 1959 and Norio Taniguchi coined the term “nanotechnology” in 1974.
Nanotechnology chiefly involves designing, manufacturing, processing and application of polymer materials filled with nano-particles and/or devices of nano range which are <100 nm in size . It can be foreseen that for customer’s sake nanotechnology will create a major drive for the development of advanced packaging systems, as they display specific and improved physicochemical properties and extends the shelf life of products.
2. Classification of Nano-materials
Nano-materials are categorized as nanoparticles (NPs), nano-clays (NCs) and nano-emulsions (NEs).
Various organic, inorganic and combined fine nano-particulates (100 nm or less) are incorporated into plastics to improve the properties over those of conventional counterparts.
(i) Nano-cellulose: A polysaccharide, cellulose is the most common type of polymer and gives plant cell walls their strength. Nanocellulose is nanostructured cellulose with a diameter of less than 100 nm and a few micrometres in length that can either be nanocrystals or nanofibres . In order to increase the strength, mechanical characteristics, homogeneity and biodegradability of paper and composite materials, nanocellulose is utilized .
(ii) Starch nanocrystals: By breaking down starch granules using a variety of physical and chemical processes, nano starch is created . Starch nanoparticles have a high surface area per unit volume and at least one dimension smaller than 300 nm . The features of starch nanoparticles, often referred to as starch nanocrystals, include strength, flexibility, biodegradability, water impermeability, thermal conductivity and barrier properties .
(iii) Protein-based nano-particles: In order to improve the strength and barrier qualities, such as the water barrier properties, protein-based nanoparticles are utilized in food packaging . When added to protein-starch-based biocomposites, peanut protein and zein nanoparticles were found to increase the materials’ strength, temperature resistance and moisture barrier qualities .
(iv) Chitosan nano-particles: Chitosan present in the exoskeletons of crustaceans, arthropods and in cell wall of fungus has a great potential to be used as nanoparticle for use in packaging, since it is safe for the environment, non-toxic and has great antibacterial capabilities . When chitosan is added to a biodegradable polymer, such as polylactic acid films, it enhances the physical, mechanical and barrier properties as well as moisture impermeability due to the hydrophobic nature, hydrogen formation and reduced rate of moisture diffusion, due to covalent bond between chitosan nanoparticles and biopolymer [9, 21].
2.1.2 Inorganic nano-particles
(i) Carbon nanotubes: Carbon nanotubes are carbon allotropes that have been rolled up into cylindrical shapes with a diameter in the nanometer range. They can be either single-walled nanotubes or multi-walled nanotubes made up of many concentric cylinders . The mechanical and anti-bacterial qualities of the polymer used in packaging are enhanced by the inclusion of carbon nanotubes . In order to monitor the concentration of oxygen in modified atmospheric packaging, carbon nanotubes are used in the construction of oxygen sensors . A synthetic polymer matrix used for food packaging contains carbon nanotubes to give antibacterial characteristics and intelligent sensors that may identify food spoiling .
(ii) Silver nanoparticles (AgNPs): In order to extend food’s shelf life, silver nanoparticles are incorporated in food packaging, as they are effective against various gram-positive as well as gram-negative bacteria . For creation of active food packaging, AgNPs are utilized as an antibacterial agent in both biodegradable (polysaccharides like cellulose, starch and chitosan) and non-biodegradable (polyethene, polyvinyl chloride and ethylene-vinyl chloride) polymers .
(iii) ZnO nanoparticles: By producing Zn2+ ions and ROS, which damage cell organelles and result in cell death, ZnO nanoparticles exhibit antibacterial action against different bacteria, including E. coli, Staphylococcus aureus, Listeria monocytogens, Salmonella enteritids and various others. When added to the polymer matrix, ZnO NPs enhance the barrier, antibacterial and mechanical properties of composite films .
(iv) Titanium Dioxide (TiO2) Nano Particles: White metal oxides called TiO2 NPs are used in nano-composites for food packaging to block UV rays and improve the chemical, mechanical and barrier properties of the films . Titanium dioxide has antibacterial properties because it produces free radicals and reactive oxygen species (ROS), which interact with bacterial cells and kill them . Due to its chemical stability, affordability, lack of toxicity and environmental friendliness, TiO2 is a powerful photocatalyst because it act as scavenger of oxygen and ethylene [18, 33].
The term “nanoclay” is typically used to describe layered crystalline silicates, each of which is composed of octahedral or tetrahedral sheets . In order to enhance the physical and barrier qualities of plastic materials, nanoclay is frequently employed in food packaging . The most common form of nanoclays is a platelet with a flaky, soft texture, a low specific gravity, and a high aspect ratio. Due to their resemblance to thermoplastics and high aspect ratio, montmorillonites (MMT-Na+) and organophilic MMT are frequently utilized in packaging . Starch thermoplastic’s mechanical and barrier qualities as well as synthetic polymers’ capacity to break down biologically are improved by nanoclay .
The droplet sizes of the nanoemulsions, which are typically between 200 and 100 nm, are comparable to those of microemulsions . Nanoemulsions are thermodynamically metastable when phase separation develops over time, just like conventional emulsions. However, due to the lower attractive force between the tiny droplets, nanoemulsions have kinetic stability, which prevents droplet aggregation and gravitational separation . In contrast to thermodynamically stable microemulsions, the nanoemulsions are not impacted by changes in temperature or pH. For their preparation, fewer surfactants are needed. In addition to affecting a nanoemulsion’s optical characteristics and stability, the droplet size also affects its rheological and releasing characteristics. Among the food pathogens that nanoemulsions are effective against are gram-negative bacteria. They can be used to clean the surfaces of food processing plants and lessen surface contamination. Additionally, nano-emulsion therapy prevents the develo pment of Salmonella typhimurium.
2.4 Applications of Nano-material in the field of Food Packaging
2.4.1 Improved Packaging:
In improved packaging development, nanomaterials are mixed into the polymer matrix to improve mechanical and physical properties of the packaging such as gas barrier properties, resistance to temperature and humidity, mechanical strength and flexibility . A variety of nanoparticle reinforced polymers, also termed as nanocomposites have been developed, which typically contain up to 5% w/w nanoparticles and they improve barrier properties of packaging such as reduction in oxygen and carbon dioxide permeation for up to 80–90%. Scientists reported that excess clay loadings in ethylene-vinyl alcohol (EVOH) copolymer-based nanocomposite films lead to the reduction of tensile properties and optical transparency due to the formation of clay agglomerates . With the addition of only 3% (w/w) clay, the oxygen (by 59%) and water vapour barrier (by 90%) properties of the nanocomposite films were improved in comparison to the material without added clay nanoparticles.
2.4.2 Smart Food Packaging
The improvement of food packaging with smart or intelligent functions can be performed using nanoparticles to monitor chemical or biochemical, or even microbial development inside the food and or the environment surrounding the product. Therefore, specific pathogens and specific gases nanosensors can be used for food spoilage detection .
Smart packaging adapts to its surroundings, fixes itself, or warns the user about contamination and/or the presence of diseases. The German company Bayer, a global leader in chemicals, makes a clear plastic film called Durethan that contains clay nanoparticles. Since the nanoparticles are spread throughout the plastic, they can prevent fresh meats and other goods from coming into contact with oxygen, carbon dioxide or moisture. The plastic is also stronger, lighter and more heat resistant thanks to the nanoclay.
Researchers have developed a molecular barrier that helps stop oxygen from escaping by enclosing nanocrystals in plastic. A plastic beer bottle being developed by Nanocor and Southern Clay Products (Austin, USA) may have an extended shelf life of 18 months. Ingenious packaging that releases a preservative if the food inside starts to degrade is being developed by researchers in the Netherlands. This preservative package uses a bio switch created using nanotechnology to “release on command.” “Smart” food packaging will alert you if food is spoiling or has gotten oxygen inside. Such packages are already used in breweries and dairies and consist of nano-filters that can remove micro-organisms and even viruses.
2.4.3 Food Nano-sensors
Nanosensors have a great potential for fast detection, identification and quantification of pathogen microorganisms, decaying substances and allergy-causing proteins. Custom-made nanosensors used in smart packaging are used for food analysis (detecting toxins, chemicals and food pathogens) detection of flavours or colours etc. . Food packaging can be equipped by nanosensors which are sensitive to humidity, gases formation or temperature changes. For example, when gas is formed due to spoilage of food, the packaging changes the colour of the indicator and thus alerting the customer to the unsuitability of the product. Moreover, it can be successfully used for real-time monitoring of food freshness status and reduce the requirement for determining the shelf life of the food, since the nanosensors can respond to certain chemical markers, pathogens and toxins in food .
Bio-nanosensors are the result of combining the biosensors and nanotechnology. To detect contamination and regulate the food environment, nanomaterials are used as sensors as they are able to detect microbial and other food contaminants. The packages could also be designed to allow air and other enzymes to move out of package but not allowed to enter, which enhances the shelf life of product along with reducing the need for chemical preservatives in our foods. Therefore, nanomaterials can be used as nanosensors and nanotracers with almost unlimited potential by the Food Industry.
2.4.4 Active Packaging with Nano-Material
Another important potential application of nanoparticles is that they can be incorporated into the packaging material which not only enhances the physical and chemical properties of the package, but also improves the performance and functional properties (antimicrobial, antioxidant, scavenger), therefore, elevating the shelf life of food materials.
Researchers reported the challenges of using nanotechnology to create low-cost packaging that assists in functionality, weight and ease of processing. The new hybrid plastic, comprising of polyamide and nano-clay makes it much more difficult for oxygen to pass through it. Moreover, when nano-particles are inserted on the packaging material, they can break ethylene gas and delay the ripening process and in turn maintain the freshness of fresh fruits and vegetables and enhance their shelf-life.
Nanotechnology has the versatility to deliver innovative food packaging materials. Nano-composites can improve the mechanical, chemical and functional properties of packaging. Nano-materials are often used to make packaging that keeps the perishable fresh for a long time. Smart food packaging, integrating nano-sensors, can even provide consumers with information about the status of the food they contain. Food packaging contains nanoparticles which warn consumers when the product is no longer fit for consumption. Nano-sensors can warn the consumer if the food inside the package has become rotten or can notify us of the exact nutritional status of food. In fact, nanotechnology will change the manufacturing operations of the entire packaging industry.
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About the Authors:
1. Ritupriya Jaiswal
Department of Food Science & Technology
Khalsa College, Amritsar.
Email ID: email@example.com
2. Dr. Gursharan Kaur
Department of Food Science & Technology
Khalsa College, Amritsar.
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