Soy Protein
Soy protein has been used since 1959 as an ingredient in a variety of foods for its functional properties, which include emulsification and texturizing. Soy protein is used in many applications [143]. Recently the popularity of soy protein has risen, mainly because of its health benefits. It has been proved that soy protein can help to prevent heart problems. Soy protein films do not have as good mechanical and barrier properties as most protein films, due to their hydrophilic nature. They are used to produce flexible and edible films.
2.4 Biopolymer Type Number 3: Polysaccharides
Polysaccharides are among the most widespread organic compounds in the plant kingdom and used in many applications [144]. Polysaccharides play essential roles in the life processes of all plants. They can be divided into several broad groups according their functions, i.e., structural polymers (cellulose), protective polysaccharides (pectin and hemicelluloses) and reserve polysaccharides (starch). Further, polysaccharides can form glycoconjugates with proteins and lipids resulting in biological macromolecules in the cell wall and cell membranes, and play important roles in many physiological and biochemical processes.
2.4.1 Starch
Starch is a complex carbohydrate and one of the largest molecules in nature found chiefly in seeds, fruits, tubers, roots and stem pith of plants, notably in corn, potatoes, wheat, and rice. Starch is a polymer of D-glucose organized in two major constituents of huge molecular weights. Amylose contains amorphous and crystalline regions [145, 146]. Amylopectin is used in high-performance flocculents and as non-ionic surfactant [145]. To improve their resistance to shock and moisture, polyolefins were added in small quantities (about 10–15%) or in large proportions up to 85–95% to starch. Those polymer mixtures disappeared during the biodegradation process leaving small fragments whose degradation time was a function of their carbon chain length. Supol (Supol, Germany) Potato flour is submitted to a thermal treatment under pressure. Pellets can be injected to produce single-use dishes which are microwavable and which are compostable or can be added to animal food. Evercom (Comstarch, Japan) plasticized maize starch can be injected to make small parts for catering or for horticultural applications. This product is compatible with other biopolymers such as PHBV, PLA, PCL polyesters. Native starches differ in the amylose/amylopectin ratio depending on their botanic source, such as native starches are composed of 20–30% amylose and an additional amount of amylopectin, amyloseenriched starch may contain up to 84% amylose while waxy starches consist of nearly pure amylopectin. The main applications are for producing mulch films, shopping bags, food packaging (yogurts), nappies, medicinal and personal hygiene products [147, 148].
2.4.2 Cellulose and Cellulose Derivative
Cellulose is a polysaccharide that is the main constituent of all plant tissues and fibers. The name cellulose, from Latin cellula, was coined in 1838 by French chemist Anselme Payen. Special forms of cellulose fiber are found in most plants in the leaves and stalks, with cotton fiber (95% cellulose) [149]; wood (about 50%) being the principle industrial sources of cellulose [150]. Because of its ubiquity in the plant kingdom, cellulose is arguably the most abundant polymer on earth, with billions of tons produced annually through photosynthesis. The strong glucosidic bonds ensure the stability of the cellulose in various media. Cellulose is mostly insoluble and highly crystalline. Chemical reactions such as esterification are conducted on the free hydroxyl groups to improve its thermoplastic behavior. The main uses of cellulose are for paper, membranes, dietary fibers, explosives and textiles [151]. CellophaneTMis a blend of cellulose and diaphane [152]. A transparent paper-like product that is impervious to moisture and used to wrap candy, cigarettes, etc. The name was coined in 1912 by Swiss chemist Jacques Edwin Brandenberger, the invention of the material dates from 1908. Cellophane films are obtained by dissolution of cellulose in a sodium hydroxide and carbon disulphide solution (Xanthation) and then by recasting in a sulphuric acid bath. Degradation takes place after six weeks of composting. Cellophane films are mainly used in food packaging where they are valuable for their barrier properties against microorganisms, gases and smells. Cellulose acetate is mainly used in the synthesis of membranes for reverse osmosis.
Cellulose is the principle part of most plant cell walls, and is currently of interest because of processes for paper making, and as a major structural component of textile fibers such as (Gossypium spp.), ramie (Boehmeria nivea), jute (Corcorus capsularis), flax (Linum usitatissiumum) and sisal (Agare sisalana). Surgical cotton is actually made from wood. Cellulose used as biopolymer, biomaterial, drug delivery, bacterial microparticles [153, 154].
Bacterial cellulose is synthesized in a process whereby the polymer material is extruded from the bacterial cells. Most cellulose-producing bacteria (i.e., Acefobacter) extrude cellulose as a ribbon-like product from one fixed site on the cell surface. This results in a network of interlocking fibers forming. Bacterial cellulose is produced under conditions of agitated fermentation. Bacterial cellulose is a water-insoluble material that has a large surface area because of its large network of fibers; bacterial fibers have roughly 200 times the surface area of fibers from wood pulp. This, coupled with their ability to form hydrogen bonds, makes them unique when used as suspensions, they have pseudoplastic thickening properties. The bacterial cellulose is used for dressing chronic wounds [155], nanocomposites [156], cancer treatment [157], natural rubber latex formation [158], antimicrobial food packaging applications [77], biocomposite [159], gravity-driven oil/water separation [160] and many others.
2.4.3 Hemicellulose
Hemicelluloses are a group of substances which occur in association with cellulose, and are usually a mixture of xylans, xyloglucans, arabinogalactans, glucomannans and galactoglucomannans. Hemicellulose is one of the most abundant polysaccharides after cellulose. Hemicelluloses were used as feedstock for producing sugars. Hemicelluloses are mostly heteropolysaccharides classified according to the sugar residues present, namely xylans, mannans, arabinans and galactans, and they are either linear or branched polymers. Xyloglucan is used as a barrier film [161].
2.4.4 Chitin and Chitosan
Chitin was discovered in 1811 by Braconnot and was initially termed fungine because it was discovered in mushrooms [25], it is derived from shrimp, crab, Antarctic krill, and cultivated fungi. It was later in 1823 that Odier gave the name chitin to the same material discovered now in the elytrum of the cock chafer beetle based on the Greek term chitos, meaning coat. Chitin as a natural polysaccharide is a tough, semitransparent horny substance; the principal component of the exoskeletons of arthropods and the cell walls of certain fungi.
Chitosan is known as soluble chitin [162–167]. Chitosan is produced commercially by deacetylation of chitin. It has many uses: diluent, binder, drug carrier, drug release, site specific drug delivery, absorption, enhancer, carrier, anticancer, anticoagulant, antiviral, antioxidant, tissue engineering and food technology. Chitosan is soluble in water and in some organic solvents. The difference between chitin and chitosan is defined by their solubility in a dilute solution of weak acids. Chitosan dissolves in dilute acetic acid. It presents a unique combination of properties, brought about by its polysaccharide structure, large molecular weight, and cationic character. Chitin and chitosan are biocompatible and present antithrombogenic and hemostatic properties. These polymers can be extruded to make films for packaging applications. Chitosan is used in many applications including: hydrogel, tissue engineering, drug delivery, tissue repair.
Chitosan is the partially or fully deacetylated form of chitin. The chitosan deacetylation degree is usually in the range between 70% and 95%, and the molecular weight is also between 10 to 1000 kDa. Its application in the tissue engineering and drug delivery fields is wide ranging from cartilage, bone, vascular grafts and skin to substrates for cell culture. Biologically renewable, biocompatible, biodegradable, non-toxic and non-antigenic properties of chitosan make it a bio-functionally useful biomaterial. In addition, hydroxyl and amino groups of chitosan can be modified chemically to provide a high chemical diversity. It also has bio-adhesive properties. Chitosan exhibits different behaviors