Agricultural wastes are useful resources that can be employed as a natural source to synthesize bio-based packaging. Scientists synthesize innovative materials from various beneficial compounds such as carbohydrates, proteinous substances and essential oils. As a result, using trash as a source of packaging material will be able to help decrease expenses incurred by the food industry drastically and improve the quality of packed foodstuff. Moreover, some chemical and biological materials such as essential oils and nanoparticles cannot be implemented in food formula directly. Therefore, the application of such substances as a part of food packaging can be a proper solution. Various agricultural and food-based wastes should be considered and evaluated for their potential application in the packaging industry.
Different packaging styles have been invented worldwide, owing to their numerous exceptional benefits, some of them being their cost effectiveness as well as for being environmentally friendly. The use of edible films and coatings has attracted significant attention. Edible films and coatings are digestible for the human body and environment. Edible materials are classified as edible coatings, films and sheets based on their usage. Edible coatings are the liquid form of edible materials that can also incorporate other chemical and biological components such as nanoparticles. The thickness of edible coatings is 0.050mm. Edible sheets are thin layers wrapped around food. In contrast, edible coatings are often sprayed on the surface of food or food immersed in various edible coatings such as proteinous compounds.
Numerous investigations on the production of edible coatings based on various fruits, vegetables, polysaccharides, proteinous substances, essential oils and antibacterial agents have been done. Coatings and films play a significant role in extending shelf life, owing to crucial properties present in them that can fight against food pathogens, including lipid oxidation, enzymatic activity, maintaining chemical quality and boosting the microbiological quality of packed food. Various antibacterial, antifungal and antioxidant ingredients have been introduced into edible materials to improve their microbial quality and reduce fatty acid oxidation, resulting in minor enzymatic browning and texture changes during the shelf life.
Polysaccharide-based Edible Coatings:
There has been a significant interest in applying polysaccharide-based edible coating with essential oils (EOs), owing to their potent antioxidant and antimicrobial characteristics. Owing to their ease of extraction and application, chitosan, pectin, alginate and gelatine are among the most commonly used inedible coating polysaccharides. The hydrophilic nature of polysaccharide-based edible coatings has limited their use for a specific cuisine. Starch is naturally biodegradable and renewable biopolymer, owing to its vast availability and low cost. Disposable tableware, industrial items and food edible coating and packaging have all been made with starch polymers. Amylose and amylopectin molecules are the building blocks of starch. Due to starch’s physical nature and structure, mechanical properties and moisture/gas barrier capabilities are among the deficiencies of starch-based edible coatings.
Chitosan Edible Coatings:
Chitosan is a non-toxic polycationic heteropolysaccharide generated through alkaline deacetylation of chitin, which is mostly recovered from shrimp, prawn and crayfish shells as one of the most readily available wastes from fisheries. Chitosan has been employed for various medical and industrial reasons in recent decades, owing to its natural properties and low extraction costs. Furthermore, chitosan has attracted much attention in the food industry as a natural source of polymers with a wide range of applications in food packaging. Chitosan biopolymers have exhibited antimicrobial activities against various bacteria, fungi, yeasts and moulds. Edible biodegradable coatings are made of natural polymers such as polysaccharides and proteins, which reduce hazardous chemical consumption and boost the cost-effectiveness of packaging, owing to the use of wastes as natural sources of edible coatings.
Fruits and Vegetable-based Edible Coatings:
Global population growth, drought and environmental destruction are now a major concern. Hence, the rising attempts made to minimize food waste through proper packaging helps prolong shelf life, apart from being environmentally friendly. These wastes or remains such as seeds, skins, juices and pulps are rich sources of antioxidants, vitamins and other nutritious materials that can be reproduced to produce new materials. Also, they are attractive candidates for making films and biodegradable coatings. Plants with higher antibacterial characteristics are more often used, since the films’ mechanical characteristics are enhanced and the growth of microorganisms would slow down. Aloe Vera was used in different studies and the derived edible coating has gained much attention, owing to its tastelessness and odour-free nature. Thus, it would not cause any undesired changes in the food. In addition, it contains nutritious materials and active vitamins such as sugar, saputin, vitamins and amino acids. It is capable of hindering dehydration of the fruit juices coated with it.
Essential Oils in Edible Coatings:
Essential Oils (EOs) are known for their antimicrobial, anti-browning and colourant properties, owing to their hydrophobic and volatile structure. Thus, incorporating EOs in edible coatings increases their functionality and is considered to be a unique novel method for increasing the shelf life and maintaining the quality of fresh food. Although, the addition of EOs reduces the physical attributes of edible coatings, when compared to synthetic polymers such as LDPE, the benefits of using such EOs edible coatings include reduced odours, increased active substances and sensory aspects. Coatings containing EOs have been made from natural and biological materials, including lipids, proteins and polysaccharides. Numerous studies on using essential oils against various microorganisms, including Staphylococcus aureus, Bacillus subtilis, Serratia marcescens and Salmonella enteritidis have been conducted and results showed to inhibit the growth.
Application of Nanoparticles in Edible Coatings and Films:
The synthesis and application of innovative nano-biocomposites incorporating various biological nanoparticles have emerged as a leading technology in recent years. Edible coatings and films are an appropriate matrix for embedding different nanoparticles to increase nanoparticle contact with robust microorganisms in packed food. Silver, copper, titanium dioxide and zinc among other nanoparticles have been included in nanocomposites. Furthermore, chitosan, kefran, shellac, cyclodextrin and starch are the matrices used to manufacture nanoparticle-containing edible coatings and films. Chitosan is widely used as a non-toxic biopolymer. Chitosan biofilms and coatings are an ideal matrix for encapsulating different nanoparticles. Numerous studies on the utilization of nanocomposites containing chitosan and nanoparticles have been done.
Lipid-based Edible Coatings:
Natural resources produce lipids that constitute hydrophobic bonds, owing to their unique properties. They can be utilized to cover a variety of foods either alone or in combination with other materials. Lipid-based coatings are shinier and lose lesser humidity. The primary components of these compounds are derived from plant and animal fats. Essential oils are the other materials in the lipids category. Owing to the presence of terpenoids and terpenes, these compounds are hydrophobic and some of them have antibacterial properties. EOs are employed to improve the antibacterial properties of edible coatings and films. Waxes are a type of lipid with a high molecular mass. They are derived from both plant and animal sources and since they reduce humidity loss and evaporation, their uses for edible coatings are gaining popularity. Different forms of waxes used to create coatings include synthetic waxes, carnauba wax, candelilla wax, rice bran wax and beeswax.
In recent years, global emphasis has been laid on packaging that extends shelf life, maintains food quality and significantly reduces production costs. Furthermore, environmentally friendly packaging made from agricultural as well as food and plant waste is growing globally. Edible coatings are set to be replaced by artificial packaging shortly, owing to their promising antibacterial, chemical and physical capabilities. It is worth noting that using essential oils, nanoparticles and agricultural wastes together may have synergistic effects, which can help in ensuring a highly effective packaging for the Food Industry.
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