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An Overview of Natural Biopolymers in Food Packaging

Santosh Kumar 1,*, Indra Bhusan Basumatary 1, Avik Mukherjee1,*, and Joydeep Dutta2,*

1 Department of Food Engineering and Technology, Central Institute of Technology Kokrajhar, Kokrajhar 783370, Assam, India

2 Functional Materials, Department of Applied Physics, SCI School, KTH Royal Institute of Technology, Hannes Alfvéns väg 12, 114 19, Stockholm, Sweden

* Corresponding authors: Santosh Kumar, s.kumar@cit.ac.in; Avik Mukherjee, ak.mukherjee@cit.ac.in; Joydeep Dutta, joydeep@kth.se

CHAPTER MENU

1. 1.1 Introduction
2. 1.2 History and Background
3. 1.3 Classification
   1. 1.3.1 Polysaccharide-Based Biopolymers
   2. 1.3.2 Protein-Based Biopolymers
   3. 1.3.3 Lipid-Based Biopolymers
   4. 1.3.4 Biopolymers Synthesized from Bio-derived Monomers
4. 1.4 Advantages and Disadvantages
5. 1.5 Properties and Applications
6. 1.6 Conclusion and Perspectives

1.1 Introduction

The prefix "bio" in the term "biopolymer" signifies that these polymers are of biological origin, i.e. inherently produced in living organisms. Biopolymers, bio-based polymers, biodegradable polymers, and bioplastics are used synonymously in specific contexts, but each term has a different meaning. Bio-based polymers are materials produced from natural resources such as plants, animals, and microorganisms that can be biodegradable (e.g. starch, polylactic acid [PLA]) or non-degradable (e.g. biopolyethylene) [1]. Biodegradable polymers are materials that completely degrade when exposed to soil, air, water, and microorganisms over a specific time period. Biodegradable polymers may be natural (e.g. starch, cellulose, proteins, lipids) or synthetically produced (e.g. polycaprolactone and polybutylene succinate). A bioplastic is a plastic polymer manufactured from a natural or renewable source, and it is biodegradable [2]. Biopolymers are primarily composed of repeating units of monomers made of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) and are found in living organisms such as plants, animals, and microorganisms. Based on this definition, biopolymers include bio-based polymers and natural polymers, including biodegradable polymers such as polysaccharides, proteins, lipids, and polynucleotides (DNA and RNA). However, biopolymers such as DNA and RNA have complex molecular structure, in which monosaccharide, protein/amino acids, and functional groups such as phosphate groups are joined together by complex intramolecular interactions like hydrogen bonding, disulfide bridges, and hydrophobic interactions to create three-dimensional (3D) structure and termed as bio-based heteropolymers or biomacromolecules [3].

The physicochemical properties of biopolymers such as stiffness, elasticity, conductivity of electricity and heat, resistance to corrosion, appearance such as transparency, and color depend on the type(s) of monomer, degree of polymerization, and type(s) of intramolecular bonds. Compared to synthetic polymers obtained from fossil fuels, biopolymers offer the obvious advantage of eco-friendly degradation, which leads to effective waste management and a healthy environment. The biopolymers are excellent candidates for various applications such as food, pharmaceuticals, and cosmetics and in several industries including packaging, agriculture, textiles, and water treatment due to their biocompatibility, non-toxicity, and biodegradability [4-6]. However, impact strength, tensile strength, permeability, and thermal stability of biopolymers are relatively inferior compared to synthetic (i.e. petroleum-based) polymers. Reinforcement of fillers or additives in biopolymers significantly improves the mechanical properties, such as tensile and impact strengths of the resulting composites, and thermal and optical properties [7-9]. Cellulose, chitosan, starch, polyvinyl alcohol (PVA), polylactic acid (PLA), polyglycolic acid (PGA), polycaprolactone (PCL), polyhydroxybutyrate (PHB), polybutylene succinate (PBS), etc. have gained substantial attention as biopolymers in food packaging applications [5, 6, 8].

Synthetic polymers like polyethylene (PE), polypropylene (PP), nylon, polyester (PS), polytetrafluoro-ethylene (PTFE), and epoxy are commonly known as plastic and are derived from petroleum hydrocarbons [10]. These materials are still an integral part of our human life, and they have found their way into our daily routine. The demand for petroleum-based polymers in our commercial world is increasing because of their versatility, high mechanical strength, flexibility, resistivity, transparency, chemical inertness, low mass, and low cost [11]. Moreover, these plastic do not readily react with the product with which they are in contact, and they have excellent resistance to water, gases, temperature, and chemical degradation. Synthetic plastics are made from petroleum hydrocarbon, which is a non-renewable resource, and they emit large quantities of greenhouse gases during production [11]. In addition, burning of plastics can emit toxic chemicals such as dioxins [12]. Plastics that are used for short time periods and single-use plastics should not be made of synthetic plastics due to their low density and slow decomposition. As reported by various environment protection agencies, plastics alone account for more than 25% (by volume) of the total municipal solid waste generated. Synthetic plastics-based food packages/containers and utensils take many years, sometimes even more than a hundred years, to degrade in the environment (Figure 1.1a), whereas natural biopolymer-based food packages/containers and utensils decompose within a few weeks to a few months (Figure 1.1b). Thus, synthetic plastic-based food packages and containers become a significant problem for the environment and living beings. They impact the quality of air, water, and soil and indirectly plant, animal, and human lives. Accumulation of large amounts of plastic waste in the marine ecosystem causes choking and entanglement of marine flora and fauna [13].

Figure 1.1 Lifecycle of (a) synthetic plastics-based food packages/containers and (b) biopolymer-based food packages/containers and utensils.

As an alternative to petroleum-based plastics, biopolymers have significant potential to be used in food packaging applications [5, 6]. These would help to reduce the impact of synthetic plastics waste because of rapid degradation of biopolymer-based plastics in the environment. They are decomposed by the enzymatic activity of naturally occurring microorganisms in the environment such as bacteria, fungi, and algae and by chemical processes such as chemical hydrolysis. During biodegradation, biopolymer-based food packages and containers are converted into simple organic molecules, carbon monoxide (CO), methylene (CH), water, biomass, and other natural substances. Biopolymers such as chitosan and PLA are naturally recycled by biological processes (Figure 1.2). Thus, biopolymers are characterized by easy disposal, recycling, biodegradation, and composting and by their eco-friendly nature. In addition, some of them have advantageous features such as inherent antimicrobial and antioxidant activities, because of the presence of different functional groups in their polymeric chains. Despite these advantages, biopolymers lack adequate mechanical and barrier properties, which makes them unsuitable for use as food packaging [14]. Many researchers have focused on this and propose the use of crosslinkers such as nanofillers and blending of two or more biopolymers to address these challenges. This chapter provides a comprehensive overview of various biopolymers and their properties and applications in food packaging and preservation.

Figure 1.2 Lifecycle of chitosan (left) and PLA (right).

1.2 History and Background

"Biopolymers" can be defined as polymers that are naturally produced or are obtained from living organisms. The repeating monomer units of biopolymers are saccharides, nucleic acids, or amino acids, and sometimes various additional chemical side chains and functional groups. Historically, biopolymers have been commonly used as food, for making clothes and houses, and as fuel for cooking. They are biodegradable in nature and are obtained from natural renewable resources, which has inspired a renaissance of research interest. Biopolymer-based composite materials are sustainable and have the potential to replace the fossil fuel-based synthetic plastics that have been used on a large scale since the industrial revolution. Fossil fuels are limited resources, and due to non-biodegradability they cause significant environmental problems. Therefore, biopolymers can be used as sustainable and environmentally friendly alternatives to synthetic plastic for food packaging applications.

Silk is an ancient protein polymer, with an amino acid composition that depends on the producing species. Silks are produced by spiders, silkworms, and several lepidoptera larvae. Bombyx mori, a silkworm, is the most popular species for silk production. This silk is characterized by fibroin fibers held together by a glue-like protein...