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2 An Overview of Biopolymers in Food Packaging Systems
Jéssica de Matos Fonseca☆, Betina L. Koop☆, Thalles C. Trevisol, Cristiane Capello, Alcilene R. Monteiro, and Germán A. Valencia
Federal University of Santa Catarina, Department of Chemical and Food Engineering, Florianópolis 88040-900, Brazil
2.1 Introduction
In the last years, polymers isolated from renewable raw materials have been studied as alternative to synthetic polymers for food packaging applications [1]. Synthetic polymers-based films are thin layers, between 50 and 80 μm. These materials have excellent barrier properties against several gases (e.g. H2O, O2, and CO2), as well as against biological, chemical, and physical contaminants [1, 2]. However, synthetic polymers are derived from petroleum, a nonrenewable resource, and they can be classified as nondegradable materials, negatively impacting the ecosystems [3]. In this sense, several researchers have focused to replace synthetic polymers by polymers from natural sources, also called as biopolymers [4–9]. Several biopolymers have been used to manufacture films and coatings due to the good film-forming properties of these macromolecules. Furthermore, these macromolecules can be isolated directly from biomass or they can be synthetized using microbial routes, as well as by means of chemical synthesis using monomers from agro-resources [3, 10, 11].
Food packaging based on biopolymers are sensitive to the relative humidity and temperature. In recent years, the development of advanced films and coatings based on biopolymers has been explored and applied to extend the shelf life of foods, as well as to improve food safety, quality, and convenience to consumers [3]. The objective of this chapter is to review the new strategies to manufacture biopolymers-based films and coatings, aiming their applications on foods, as well as the prospects and limitations of these materials for food packaging sector.
2.2 Main Polymers Isolated from Biomass
2.2.1 Casein and Whey
Milk proteins are conformed by casein and whey; casein is a milk-specific protein (∼80%) having four different proteins (αS1-, αS1-, β-, and κ-caseins). In milk, this protein form colloidal micelles with particle size between 50 and 600 nm. Caseins can be coagulated using acid compounds or enzymes (rennet), given that the coagulation method impacts the physicochemical properties of this macromolecule [12]. Acid casein is obtained after its precipitation by the exposure of the milk below pH 4.6 (isoelectric point of casein). In the enzymatic method, caseins are coagulated using chymosin (rennet) enzymes where several chemical bonds are cleaved in κ-casein. Rennet caseins are insoluble in water, and they have a pH around 7.5 [13].
Acid caseins are also insoluble in water, so they are neutralized to pH 6.7 using potassium, sodium, calcium, or ammonium to obtain caseinates, which are soluble in water. In another way, casein can be neutralized using sodium hydroxide to produce a caseinate called as sodium caseinate. Similarly, sodium, ammonium, and potassium caseinates are obtained using others neutralizing agents. Some caseinates such as sodium, ammonium, and potassium caseinates have similar physical properties, and their solutions are viscous and translucent. In contrast, solutions based on calcium caseinate are turbid [14]. Sodium and calcium caseinates are the most utilized biopolymers due to their excellent solubility, gelation, viscosity, and emulsifying and foaming properties [15].
Casein is a macromolecule having a high degree of polar groups such as carboxyl and amino, which provide good film-forming properties. Furthermore, films based on casein have acceptable gas barrier against the oxygen and other nonpolar molecules, being used as film or coating to reduce the lipid oxidation of foods [16]. In addition, films and coatings based on casein can be used as active material by blending with vitamins, minerals, dyes, and bioactive compounds (e.g. antioxidant and antimicrobial), preserving the food quality, and increasing the food shelf life [17]. Other characteristics in casein such as high nutritional value, water solubility, and emulsification capability turn this macromolecule an important material to manufacture edible packaging [18]. Table 2.1 shows some recent studies that applied casein derivatives as food packaging materials with antimicrobial and antioxidant properties.
Whey is a protein obtained from cheese or coagulated dairy products; this macromolecule is considered as by-product and represents approximately 20% of the total milk protein. Whey has a water content oscillating between 85% and 90% and a solid fraction composed of lactose, proteins, lipids, and minerals [28, 29]. In the food sector, whey can be used in liquid form, as powdered cheese whey, as lactose, and as proteins isolate or concentrate [30]. The proteins from whey are separated (concentration) and applied in the food industry due to their excellent nutritional and functional properties. Whey protein concentrate (WPC) and whey protein isolate (WPI) are obtained from the removal of nonprotein fractions to attain a protein content higher than 25% and 90%, in the final product, respectively [28].
Table 2.1 Films and coatings based on casein and whey for food packaging applications.
| Components | Production approach | Main results | References |
|---|---|---|---|
| CASa)/tannin from white peel grape, red peel grape, and oak bark | Casting | Films with improved water solubility and water vapor permeability. Bilayer films containing tannin have antioxidant property and antimicrobial activity against E. Coli and L. innocua | [19] |
| CASa)/LMPb)/glycerol/natamycin | Casting |
Films with antimicrobial activity
|