Nanotechnology-Enhanced Food Packaging. Группа авторов

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СКАЧАТЬ (EC), hydroxyethyl cellulose (HEC), hydroxypropyl methylcellulose (HPMC), and methylcellulose (MC) [33].

      Cellulose is conformed of β-D-glucose monomers, which are 6-membered rings called pyranoses. The β-D-glucose units are bonded by acetal linkages (oxygen atoms) produced from dehydration reactions between the C-1 of the pyranose and C-4 of a neighbor pyranose [34]. The equatorial position of β-D-glucose hydroxyl functional groups causes a considerable linearization of cellulose chains that facilitates the formation of long chains (fibers) of the biopolymer [34]. The hydrogen bonds between hydroxyl groups (–OH) from different cellulose chains promote the formation of microcrystalline regions, while other micro-regions are characterized by a disordered structure (amorphous) due to low amount of hydrogen bonds [35].

      Strong hydrogen bonds of the cellulose crystalline regions caused it to become mechanical and thermally resistant and insoluble in several solvents including water [36]. On the other hand, hydroxyl groups of cellulose amorphous regions are more distant between them than hydroxyl groups of crystalline regions, which allows physical interactions between cellulose and other molecules. In the case of water, cellulose is able to absorb a large number of molecules without dissolving them. This characterizes a high swelling ability of this biopolymer [33].

Cellulose ethers (MC, EC, CMC, HEC, HPMC) are biopolymers produced from substitution reactions of cellulose hydroxyl groups or alkylation and differ as to the substituting group and number of hydroxyl groups substituted (substituting degree) [33]. Generally, the cellulose etherification reactions are performed in alkaline medium using halides and alkyl sulfates as etherifying agents. The biggest advantage of the cellulose ethers in comparison with cellulose is their higher water solubility [36]. These materials are used to modify the rheology of solutions by changing of viscosity, increasing of water swelling ability, stabilizing of suspensions, gelling, and emulsifying and to form films and coatings that are more flexible than cellulose [35, 37].

Applications of films and coatings based on cellulose and its derivatives are presented in Table 2.2. It is observed that cellulose and its derivatives have the ability to form composites with a variety of other biopolymers for both active and smart packaging applications.

      2.2.3 Chitin and Chitosan

      Chitin is considered the second most abundant biopolymer in the world. Usually, this biopolymer is isolated from the exoskeletons of crustaceans such as crabs, lobsters, shrimps, squid, among others [51–53]. The molecular formula of chitin consists of the 2-acetamido-2-deoxy-β-D-glucose through a β (1,4) linkage, considered a polysaccharide (cellulose) with hydroxyl groups at position C-2 replaced by an acetamido group [51].

      Chitosan is a derivative obtained by the deacetylation of chitin (deacetylation >50%) by means of alkaline treatment [44]. Chitosan is a cationic polysaccharide with linear structure integrated by two monomers, D-glucosamine (2-amino-2-deoxy-β-glucopyranose) and N-acetyl-D-glucosamine (2-acetamido-2-deoxy-β-D-glucopyranose), linked by means of 1,4-glycosidic bonds [54]. Chitosan is a semi-crystalline biopolymer, nontoxic, biocompatible, biodegradable, and with antifungal, antimicrobial, and antioxidants properties [55, 56]. Due to these characteristics, chitosan is a biopolymer widely used in food packaging applications [55, 56].

Films based on chitosan have good permeability to gases (CO₂ and O₂) and acceptable mechanical properties; however, these materials are not good barrier against water vapor. The properties of chitosan films are impacted by the chitosan morphology and molecular weight, as well as by the N-acetylation degree, solvent type used to manufacture films, among others [54, 57, 58]. Similarly, edible coatings based on chitosan have been applied on fresh fruit and vegetables, as well as on minimally processed, decreasing the respiration rate and delaying the senescence of these products. In addition, coatings based on chitosan can be used to reduce the moisture loss and maintain the overall quality of food products [59]. Therefore, several researchers have used this macromolecule to improve the physical and mechanical properties of films and coatings, including blends with another polymers and nanoparticles. In Table 2.3, recent studies about chitosan films and coating applied in food products are listed.

      2.2.4 Collagen and Gelatin

Gelatin and its precursor collagen are biopolymers obtained from protein animal sources. Collagen is considered the most abundant protein of animal kingdom, composed of around 25–35% of total proteins of the animal body and is mostly found in the tissues as bones, cartilage, ligaments, tendons, skins, blood vessels, intervertebral discs, guts, and corneas [70]. Collagen is mainly extracted from bovine, porcine, and fish [71], while gelatin is obtained after partial hydrolysis of the collagen. Gelatin is characterized by its versatility, high digestibility, and gels melting at human body temperature. Both biopolymers show interesting physicochemical and structural properties, especially for food industries [71].

Table 2.2 Films and coatings based on cellulose and derivatives for food packaging applications.

Components	Production approach	Main results	References
WPIa)/CNFb)	Casting	Improvement of structural properties of WPIa)-based films using CNFb)for food packaging applications	[32]
Tara gum/CNCc)/grape skin extract	Casting	Colorimetric pH-sensing films with positive activation test for milk spoilage	[38]
HPMCd)/beeswax	Dip coating	Coatings with antifungal activity against A. alternata on cherry tomato fruit	[39]
CMCe)/sodium montmorillonite/TiO2	Casting	Biodegradable nanocomposite films with improved mechanical and light barrier properties	[40]
PLAf)/rosin modified CNFb)/chitosan	Casting	Films with antimicrobial activity against E. coli and B. subtilis	[41]
Gelatin/CNFb)/chitosan Starch/CNFb)/chitosan	Casting	Films with СКАЧАТЬ В начало < 12 13 14 15 16 17 18 19 20 21 > В конец