During the partial hydrolysis of the collagen, its cross-linking structure is preserved, but some peptide bonds between chains are broken. The cross-linking degree varies as to raw material used to the gelatin fabrication, and its pretreatment determines the type of gelatin that will be produced, type A or type B [75]. Gelatins type A and B are produced by acid and alkaline processes, and they have isoelectric points in a pH range between 6.0 and 9.0, and of around pH 5.0, respectively [77].
Beyond traditional food applications of the gelatin and collagen as emulsifiers, stabilizers, foaming and microencapsulating agents, these biopolymers are also applied as biodegradable films and coatings in order to extend the shelf life of food and as carriers of active agents [72, 78, 79]. The most important applications of films and coatings based on collagen and gelatin are presented at Table 2.4. The versatility of collagen and gelatin to form blends and composites and to carry different active ingredients has been observed, whose main characteristic is the antimicrobial activity.
Figure 2.1 Schematic and chemical structure of collagen (a) and gelatin (b).
2.2.5 Soybean and Derivatives
Soybean is a leguminous composed of proteins (40%), total carbohydrates (insoluble fibers and soluble saccharides) (34%), oil (21%), and minerals (ash) (4%) [93]. The proteins, water-soluble carbohydrates, and fibers are the most used soybean compounds to manufacture films and coatings, aiming food applications.
2.2.5.1 Soy Protein
The commercial soy protein is a by-product obtained from the soy oil extraction, being available as soy protein concentrate (SPC), soy protein isolate (SPI), and soy flour. SPC and SPI differ mainly by protein and carbohydrate contents. According to Koshy et al. [94], full soy flour and SPC showed carbohydrate content (34% and 18%, respectively) and protein content for full soy flour (56%), SPC (65%), and SPI (>90%).The full fat soy flour is produced by grinding soybeans into fine powders, while the SPC is prepared by defatting and removing of water-soluble carbohydrates from soy flour. Finally, the SPI is a highly refined soy flour and free of the most nonprotein components, fats, and carbohydrates [94].
Table 2.4 Films and coatings based on collagen and gelatin for food packaging applications.
| Components | Production approach | Mains results | References |
|---|---|---|---|
| Gelatin/mint essential oil | Dip coating | Coatings with antimicrobial properties used to extend the shelf life of strawberries | [78] |
| Gelatin (PSa))/ starch/acerola powder | Casting | Active films containing acerola compounds | [79] |
| Gelatin (SSb))/TiO2 | Casting | Films with antimicrobial activity against E. coli and S. aureus | [80] |
| Collagen/lysozyme | Dip coating | Coatings with antimicrobial activity against psychrotrophic bacteria used to extend the shelf life of fresh salmon fillets | [81] |
| Collagen (FSc))/sodium alginate | Casting | Biodegradable films with better structural organization | [82] |
| Gelatin (FSc))/cellulose nanofibers/palmitic acid | Casting | Films with improved physicochemical properties | [83] |
| Collagen/nisin | Casting | Films with antimicrobial activity against L. monocytogenes, S. aureus, and Lactobacillus, used to package ready-to-eat sausage | [84] |
| Gelatin (PSa))/chlorophyllin | Drying tunnel | Films with antimicrobial activity against L. monocytogenes and E. coli., used to package bologna slices | [85] |
| Gelatin (FSc))/ZnO/chitosan nanofibers | Casting | Films with antibacterial activity used to package chicken fillet and cheese | [86] |
| Collagen/chitosan/pomegranate peel extract | Casting | Films with antimicrobial activity against B. saprophyticus, B. subtilis, S. typhi, and E. coli | [87] |
| Collagen (LWd)) hydrolysate | Spraying nozzles | Coatings used to improve the growth of peas, soybean, broad bean, and rape seeds | [88] |
| Gelatin (e)BB and f) BC)/mint essential oil | Casting | Coatings with antifungal activity against B. cinerea and R. stolonifera for fruit application | [89] |
| Gelatin (FS c)) hydrolysate | Dip coating | Films were used to extend the shrimp shelf life, reducing microbial growth and lipid oxidation | [90] |
| Collagen from cowhide | Casting | Films with better structural organization | [91] |
| Gelatin (FS c))/squalene | Casting | Biodegradable packaging used to package fried fish crackers |
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