**1. Introduction**

Since the 19th century, petroleum-based polymers and plastics have occupied a major position in food packaging, but most are non-renewable, non-biodegradable, difficult to recycle, and carelessly discarded as garbage after use, thereby contributing to ecological environmental deterioration and possible health hazards [1]. Under various natural and anthropogenic forces, plastic fragments (from waste plastic containers, sheets, and films) break down into small particle sizes, further generating microplastics with a diameter smaller than 5 mm [1–3]. According to Lebreton et al. [4], over 79,000 tons of plastic waste float on the Great Pacific Garbage Patch, and the content of marine microplastics has increased rapidly from 0.4 kg/km2 in the 1970s to 1.23 kg/km<sup>2</sup> in 2015. Then Barrett et al. [5] estimated that there could be as much as 14.4 million tonnes of microplastics in the top 9 cm of sediment throughout the global ocean, which was 34–57 times more than that at the ocean surface. Moreover, microplastics have been ubiquitously detected in oceans (from the continental shelf to deep-sea waters [6], from the eastern North Pacific Ocean [3] to the Indian Ocean [7], and from coral reef to whales [8]), freshwater systems [9], airborne [10], plants, animals, and even humans [11,12]. Unfortunately, the plastic (including

**Citation:** Zhao, Y.; Li, B.; Li, C.; Xu, Y.; Luo, Y.; Liang, D.; Huang, C. Comprehensive Review of Polysaccharide-Based Materials in Edible Packaging: A Sustainable Approach. *Foods* **2021**, *10*, 1845. https://doi.org/10.3390/foods10081845

Academic Editor: Pascal Degraeve

Received: 8 June 2021 Accepted: 8 August 2021 Published: 10 August 2021

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**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

microplastics) pollution is posing a serious threat to the global environment and human health. Therefore, it is of great significance for packaging to develop a series of renewable environment-friendly materials to replace the traditional petrochemical-based materials, among which the edible material is one of the most promising materials.

Edible packaging material is a kind of sustainable material that takes natural, edible and digestible "food" as raw material and is processed by modern material forming technology. It has excellent biocompatibility and biodegradability and can be consumed by animals or humans along with the food, while satisfying the basic functions of packaging (e.g., protection and transport), thus avoiding packaging waste pollution [13,14]. The design of edible packaging was originally inspired by the "peel/skin" of fruits and vegetables, and now edible packaging has been widely applied to various forms of food packaging (e.g., films, coatings, sheets, bags, cups, trays, and lids), as shown in Figure 1. In addition, edible packaging materials are non-toxic harmless, can be in direct contact with food, and even can be used as carriers of some antioxidative, antibacterial and/or nutritional factors to improve the sensory quality and nutritional value of foods [14,15].

**Figure 1.** The major sources, types, processing methods, product forms, and food preservation applications of polysaccharide-based edible packaging.

To date, edible packaging materials include three natural biopolymers: polysaccharides, proteins, and lipids, among which polysaccharides (the most abundant natural macromolecules in nature, low processing cost and special function) occupy the most important position [13]. Polysaccharides are complex carbohydrates with varying degrees of polymerization and are composed of monosaccharides linked by α-1,4-, β-1,4-, or α-1,6-glycosidic bonds [16]. The polysaccharides commonly applied in edible packaging are cellulose, hemicellulose, starch, chitosan, and polysaccharide gums, which are used as the main matrix of packaging materials, and processed into polysaccharidebased edible films or layers by casting, coating, electrospinning, or extrusion technologies (Figure 1) [15–18].

The main value of polysaccharide-based edible packaging materials is to protect the quality of food, prolong their shelf life, and improve the functional characteristics, economic benefits, and sustainability of the packaging [15,19]. Compared with traditional packaging materials (such as paper, plastic, metal, and glass), polysaccharide-based materials have two significant advantages: Edibility and environmentally friendly performance. Compared with protein- and lipid-based packaging materials, polysaccharides have better chemical stability and processing adaptability, a greater range of sources, and lower cost. According to relevant studies, polysaccharide-based materials have good gases, aromas, and lipids barrier properties [20–24]; and even some polysaccharides and their derivatives have antioxidant and antimicrobial activities, which can effectively protect foods (e.g., fruits, vegetables, meat, aquatic products, nuts, confectioneries, and delicatessens), and extend their shelf life [15,19]. Furthermore, developing polysaccharide-based materials effectively reduces the dependence on petroleum resources, decreases the carbon footprint of the "product-packaging" system, and meets the strategic requirements of global sustainable packaging.

This article reviews the latest advances in the major polysaccharide-based edible packaging materials (cellulose, hemicellulose, starch, chitosan, and polysaccharide gums) from the viewpoints of fundamental compositions, properties, functional modification, application, and safety, highlights the potential of polysaccharides in food packaging, and provides the trends of these materials in modern packaging technology.

#### **2. Fundamental Compositions and Properties of Various Polysaccharides**

The functional characteristics of food packaging are not only related to the properties and main deterioration modes of packaged foods, but also depend on the compositions and properties of the packaging materials. Therefore, the relevant discussion of various polysaccharides has important guiding significance for analyzing the applicability of different polysaccharides in food packaging, as well as the selection of corresponding modification and application schemes. The major and minor sources, similarities and differences in compositions and structures of five polysaccharides, as well as their outstanding advantages as edible packaging are shown in Table 1. Meanwhile, the molecular structure models of different polysaccharides are shown in Figure 2.

**Figure 2.** Three-dimensional models of the molecular structure of various polysaccharides. (**a**):Cellulose (**b**): Xylan (**c**): Glucomannan (**d**): Amylose (**e**): Amylopectin (**f**): Chitosan.


Glucomannan

*Amorphophallus*

[30,31,33]

 *konjac* plants

bonds

•

Contains numerous hydroxyl groups

[16,30,31]





and firm network structure [71]

**Table 1.** *Cont.*


Although the reported polysaccharides differ in source, composition, structure, and characteristics, they generally have good gelation, film-forming, mechanical, and barrier properties, and are abundant, renewable, edible and biodegradable. In particular, there are many kinds of hemicellulose and polysaccharide gums, but the ones commonly used in packaging are xylan, glucomannan, pectin, alginate, carrageenan, and agar. These polysaccharides can be processed into different forms of packaging (including films, coatings, containers, sponges, and gels) through various material technologies, and have tremendous potential in the development and application of edible packaging in the future.

However, compared with traditional petroleum-based polymers and plastics, polysaccharide-based materials still have many disadvantages, mainly including the following:

