a) WPI: whey protein isolate.
b) CNF: cellulose nanofibers.
c) CNC: cellulose nanocrystals.
d) HPMC: hydroxypropyl methylcellulose.
e) CMC: carboxymethylcellulose
f) PLA: poly(lactic acid).
g) MC: methylcellulose
h) EC: ethylcellulose.
i) HEC: hydroxyethyl cellulose.
Table 2.3 Films and coatings based on chitosan for food packaging applications.
| Components | Production approach | Main results | References |
|---|---|---|---|
| Chitosan/gelatin/starch/sorbitol/tween/geraniol/thymol | Casting | The coatings reduced the weight loss and delayed the physicochemical alterations of strawberries | [59] |
| Chitosan/black chokeberry extract/acetic acid | Casting | Colorimetric pH indicator films with high resistance to water | [60] |
| Chitosan/glycerol/sorbitol/acetic acid | Casting | Films with antimicrobial activity against L. monocytogenes | [58] |
| Chitosan/nisin/potassium sorbate/acetic acid | Casting | Potassium sorbate and nisin reduced the resistance and increased the flexibility and hydrophobicity of chitosan films | [61] |
| Chitosan/ɛ-polylysine (ɛ-PL)/TPPa)/acetic acid | Self-assembly | Films with low solubility in water and water vapor permeability, as well as with antimicrobial activity against E. coli and S. aureus | [62] |
| Chitosan/poly (acrylic acid)/sodium chloride/methanol/human plasma/fibronectin/silicone oil | Layer-by-layer | Hydrophobic films highly stable for 28 days in food simulants | [63] |
| Chitosan/ESsb)/choline chloride based/malic acid/lactic acid/citric acid/glycerol | Thermo-pressing molding | Film with improved mechanical and barrier properties manufactured at industrial scale | [64] |
| Chitosan/montmorillonite/aromatic aldehydes/ethanol/acetic acid | Self-assembly | Hydrophobic films with good mechanical properties | [65] |
| Chitosan/carbon/L-(β)-lactic acid/glycerol | Radiofrequency reactive/magnetron sputtering | Films with acceptable barrier properties for food packaging applications | [66] |
| Chitosan/acetic acid | Casting | Films reduced the growth of mesophilic bacteria in fresh pork loins stored under vacuum, at 4 °C, for 28 days | [67] |
| Chitosan/sodium alginate/calcium chloride | Layer- by-layer | Chitosan coating layer-by-layer preserved the ascorbic acid content, antioxidant capacity, and firmness and avoid the fungal growth of on fruit bars during storage | [68] |
| Chitosan nanoparticles/TPPa)/acetic acid | Ionic gelation | Coating was effective to delay the grapes ripening, reducing the weight loss and maintaining the sugar content, soluble solids, the titratable acidity, and sensory characteristics | [69] |
a) TPP: tripolyphosphate.
b) ESs: eutectic solvents.
Collagen is produced by connective tissue cells, and it is classified as a superelastic fibrous protein. Analyzing the deconstruction of collagen fibers (Figure 2.1a), their quaternary structure is characterized by a set of collagen fibrils composed of collagen molecules, whose protein structure is tertiary [72]. This super coiling is composed of three identical or nonidentical polypeptide chains twisted together. Each polypeptide chain constitutes the primary structure of the collagen and contains around 1000 units of amino acids, whose glycine (Gly), hydroxyproline (Hyp), and proline (Pro) are in vast majority [72]. The interactions between N—H and C=O (hydrogen bonds) from amino acids are responsible by the α-helical conformation of the collagen secondary structure [73]. On the other hand, collagen tertiary structure is stabilized by means of hydrogen bonds between C–O groups from glycine and O—H groups from hydroxyproline [73]. Finally, the collagen quaternary structure is stabilized by hydrogen bonds, intramolecular van der Waals interactions, and some covalent bonds. Each collagen molecule can have until 300 nm in length and 1.5 nm in diameter [70].
There are at least 28 types of collagen, which differ as to the arrangement of amino acids composing the primary structure. The most abundant collagens are of the types I, II, and III, which manage cell differentiation, proliferation, and migration and provide the scaffolding [70]. Because of the difficult digestion of collagen by the human body, this protein is also commercialized in its complete hydrolyzed form [74].
Gelatin is composed of collagen polypeptide fragments (Figure 2.1b), whose structure is based on α-helical conformation and its combinations (β and γ conformations) [75]. Gelatin functionality depends on raw material, which causes variations of its relative fractions of peptides and molecular mass (95–100 kDa), consequently [70]. The variation of molecular mass of gelatin peptide fractions causes changes in the gelation time (setting time), gel strength (bloom), and viscosity of the biopolymer solution [76]. Gelatin bloom depends on the number of α- and β-chains, which constitute the fractions of the largest peptides, and its viscosity