Role of additives in starch-based edible films and coating: A review with current knowledge

Edible films and coating provide a potentially effective method for preserving fresh food products by reducing moisture loss, regulating respiration rate, improving surface smoothness, and or preventing microbial growth during their storage. Concurrently, starch has proven for its inexpensive, non-toxic, and widely available attribute for film and coating production. However, this biopolymer has some shortcomings when making films to preserve food. For this reason, the use of additives in its synthesis is frequent. The current review focuses on the effects of additives on the physicochemical barriers, and bioactive properties of starch-based biodegradable polymer films and coating, as well as how these composites comply with the requirements to produce edible and biodegradable food-based films and coating. These biopolymers perform magnificently as transporters for active ingredients isolated from natural sources and can be introduced into packaged foods at a controlled rate. Furthermore, the additives demonstrated antibacterial and antioxidant capabilities in the films or coating, which would improve the shelf stability of coating or packaged food. The starch-based edible films and coating have therefore garnered a significant interest as natural and environmentally friendly solutions.

Introduction

Carbohydrates, protein, lipids, or a combination of these compounds are used to make edible polymers. Even so, carbohydrates are the most widely used biopolymer in the production of films and coating due to their low cost and widespread availability [1]. Carbohydrates are the most common biopolymer used for edible film and coating due to their high availability and low cost. Carbohydrates are generally obtained from plants and can be easily modified to suit desired purposes. For example, starch and cellulose can be hydrolyzed to form simpler carbohydrates like glucose and maltose. These simpler carbohydrates can then be used as the raw material for edible polymer production. As carbohydrates are relatively cheap and widely available, they are the most viable option for producing edible polymers. As well as, the edible polymers are mainly prepared using carbohydrates, protein, lipids, or a combination of these compounds. Among these compounds, carbohydrates are the most widely worked biopolymer due to their low cost and wide availability. Thus, carbohydrates are the most viable option for producing edible polymers. Using starch from various sources in the manufacture of films and surface coating with a range of properties has been described in several types of research. Starch is a naturally occurring, biodegradable, and renewable carbohydrate found in plant stems, seeds, fruits, roots, and tubers. It is a significant source of energy for animals and humans, as well as short-term energy storage for plants. Starch is made up of two polysaccharides, one of which is amylose, and the other is amylopectin. Both are water insoluble.

When starch is subjected to specific quantities of shear pressures, thermal energy, and plasticizer, its granules irreversibly lose their semi-crystalline structure and transform into a continuous matrix. However, amylose is the cause for exceptional film-forming ability of starch, which results in films that are long-lasting, heat sealable, and isotropic [2]. Starch is used in edible films and coating as it has the capacity for forming colorless, tasteless, and translucent layers with properties similar to synthetic polymers. Starch is also used as a thickening agent in food products like gravies, sauces, soups, and pie fillings. Starch can also be used to improve the texture and consistency of foods like breads and pasta. Additionally, it is often used in baking as a gluten-free alternative to wheat flour. Finally, starch is used as a stabilizer in processed foods like ice cream, to prevent the formation of large ice crystals. Starch is used in edible films and coatings due to its unique properties. Starch is a natural polymer derived from plants and is biodegradable. It has a high water-binding capacity, is non-toxic, and is relatively inexpensive. The starch-based edible films and coatings have properties similar to synthetic polymers, such as moisture resistance, heat resistance, and flexibility. These properties make starch-based edible films and coatings suitable for use in food packaging and preservation.

Along with the properties of starch like preservation of food, protection of flavor and texture, enhanced texture, improved appearance, and reduced fat content, it can be used to create polymeric packaging materials based on starch, starch has undergone substantial research. Compared to plastics, the mechanical qualities are poorer. However, these restrictions have been reduced by the development of more recent technologies like gamma irradiation. To solve these limitations, research has been undertaken on various additives, starch sources, changes, and process parameters. Combining starch films with other biopolymers, natural fillers, hydrophobic substances, and antimicrobial/antioxidant chemicals can enhance their structural and functional properties. Incompatible polymeric blends can lead to an increase in film stiffness, whereas compatible polymeric blends can lead to a decrease in film stiffness. Additionally, blending starch and other hydrocolloids can alter the film’s water vapor permeability and oxygen permeability, as well as its mechanical properties such as tensile strength, elongation, and tear strength. Furthermore, the extent of the alteration of the mechanical features depends on the amount of starch and other hydrocolloids used in the blend [3], [4]. Moreover, incorporating hydrocolloids in edible starch coatings and films increases the viscosity of starch networks and decreases their rate of retrogradation.

Starch and other hydrocolloids interact with one another in different ways depending on their molecular weights, chemical compositions, conformations, and hydration patterns [5]. Thus, functional additives are very important to expand the efficiency by increasing the quality of edible films in terms of chemical, mechanical, and microbiological levels. These additives are added to prescribed limits so that they can enhance the functionality of these films and coatings without any harmful effects on the consumer [6]. The additives utilized can be plasticizers (glucose, sucrose, sorbitol, glycerol etc.), emulsifiers (lecithin, polysorbate 60, sodium lauryl sulfate, etc.), antimicrobials and antioxidants [7]. Furthermore, different bioactive compounds are added in the solvent mixture to increase the efficacy of edible layers during the assembly of the edible packaging mixtures. The plants synthesize these for themselves to combat different biotic and abiotic stress. These bioactive compounds are known for providing various properties and various health benefits [8]. Nanocomposite coatings based on biopolymers can be developed using techniques such as electrospinning, spray-drying, spray-coating, and layer-by-layer assembly. These techniques can be used to create coatings with thin layers of nanomaterials, such as carbon nanotubes, graphene, and nanofibers, embedded in a biopolymer matrix. The nanomaterials provide the coatings with greater strength, durability, and flexibility, while the biopolymer matrix provides the coating with improved biocompatibility and biodegradability. The nanocomposite coatings can be used for a wide range of applications, such as medical implants and devices, food packaging, and corrosion protection. Starch nanocomposite/coatings based on biopolymers are materials that are made up of starch and other biopolymers materials, such as proteins and polysaccharides. These materials are used to provide a protective coating on surfaces, such as food containers, packaging materials, and other items. They are typically produced by combining starch with biopolymer materials, using various chemical and physical processes.

The resulting nanocomposites/coatings are usually more durable and resistant to environmental conditions than traditional coatings, allowing them to provide more effective protection. They also have a range of other beneficial properties, such as improved thermal and mechanical stability and resistance to microbial growth. These materials are becoming increasingly popular for use in a variety of applications, including food packaging, pharmaceuticals, and medical devices. Starch-based films and coatings can be used to improve the barrier properties of food and packaging materials. The addition of additives such as plasticizers, emulsifiers, antioxidants, and antimicrobials can have a significant impact on the film forming ability of starch. Plasticizers can improve the flexibility of the films, increasing their flexibility and elongation. Emulsifiers can improve the film forming ability of the films, reducing surface tension and increasing adhesion. Antioxidants can protect the films from degradation by oxygen, making them more stable and durable. Antimicrobials can prevent the growth of microorganisms, increasing the shelf life of the films. The addition of these additives can improve the film forming ability of starch, allowing for its use in a wider range of applications [9]. The detailed procedure of final product development from solvent is depicted in Fig. 1.