Proteins from Industrial Biowastes: Comparison
View Latest Version
Please note this is a comparison between Version 4 by Dean Liu and Version 5 by Dean Liu.

A great amount of biowastes, comprising byproducts and biomass wastes, is originated yearly from the agri-food industry. These biowastes are commonly rich in proteins and polysaccharides and mainly discarded or used for animal feeding. 

  • bioplastic
  • protein
  • biowaste
  • valorization

1. Introduction

The accumulation of plastic wastes is a globally recognized problem that involves an extremely negative impact on the environment [1]. The exceptionally low biodegradability of fossil-based plastics, together with the massive production scale associated with the plastic market over the past 60 years, has generated a huge accumulation of plastics in landfills and the oceans [2]. To illustrate the magnitude of the problem, considering that almost 400 Mt of plastic waste is generated every year [3], there is currently more than 1 ton of plastic/person alive in the world. However, in spite of the recent efforts made in this field to shift from a fossil-based to a bio-based circular economy model, only 20% of plastic is collected for recycling, of which only 3% is reused [4][5]. The rest is incinerated, landfilled, or disposed of into nature, a large part of which is ending up in the oceans [6]. In this sense, European Union Directive (EU) 2019/904 aims to prevent and reduce the impact of certain single-use plastic products on the environment, especially the marine environment, and on human health. Consequently, the future of the plastics industry needs to be driven by sustainability issues, where the bioplastic sector is a crucial building block for a circular economy scenario [7][8].

The most accepted definition of the term bioplastic, which has been controversial among plastic industrial associations and environmental organization, is given by European Bioplastics [5]. According to this association, any plastic material can be denoted as a bioplastic if it is either bio-based, biodegradable or displays both properties. Consequently, bioplastics embrace a whole family of materials with different properties and applications, ranging from biodegradable fossil-based polymers, such as poly(butylene adipate-co-terephthalate) (PBAT) or polycaprolactone (PCL), to non-biodegradable bio-based polymers, such as bio-based polyolefins (e.g., bioPE and bioPP) or polyesters (e.g., bioPET) [9]. However, the ecofriendliest bioplastic group is formed by biodegradable and bio-based polymers. This group comprises biodegradable aliphatic polyesters produced by fermentation of biomass, including polylactates (PLA), polyglycolates (PGA), polyhydroxy butyrate (PHB), polyhydroxy valerate (PHV), etc., and polymers extracted from renewable sources, also known as agropolymers, which include polysaccharide-based polymers (e.g., starch, cellulose, and cellulose derivatives) and protein-based polymers that can be extracted from animal or plant sources [10][11]. Currently, a big amount of the food produced worldwide (~30%) is discarded by the agri-food industry, being considered as byproducts or wastes [12]. These food biowastes could be reused as raw materials for the emerging bioplastics sector since their proteins, carbohydrates, lipids, and other compounds can be used for this application [13]

Agropolymers are considered the most eco-efficient bioplastic source in terms of the ratio between the added value of their potential applications and the environmental impacts associated with them [14]. They consist of a carbon backbone with different side groups that can form inter-/intra-molecular H-bonds. It is precisely the ability to temporarily disrupt these H-bonds and cause flow into new material shapes that allows forming plastic materials by conventional polymer processing techniques (e.g., casting, thermoforming, compression molding, extrusion, and injection molding) [15]. However, despite the unquestionable importance of bioplastics for enabling a more sustainable circular economy [16], they only cover approximately 1% of the global plastic market, accounting for 2.11 Mt in 2020 [5]. About 60% of the bioplastic market corresponds to biodegradable polymers and 20% to agropolymers (over 420 kt). Among them, starch and cellulose are abundant and low-priced raw materials [6]. Unfortunately, they typically require complex processing before they can be properly used as bioplastics. These processes, including fermentation or functionalization, typically increase their costs and, as a result, reduce their efficiency in the replacement of conventional plastics.

In contrast, an emerging ecofriendly and cost-efficient alternative to plastics is based on the use of protein which can be easily processed for many applications [17][18]. Moreover, protein may be inexpensively extracted from many sources that are also abundant in nature. Interestingly, global food biowastes represent about 1300 Mt/year, according to the Food and Agriculture Organization (FAO) of the United Nations [19]. This biomass may be regarded as a potential source that can be used in the protein-based bioplastic sector, competing with other uses (e.g., biofuel). However, some problems related to the collection of food biowastes, due to their extremely wide dispersion, still impose a barrier to their efficient application at large scales [20]. Other more interesting alternatives are currently being considered for the valorization of proteins, such as the use of agri-food co-products from the starch, oil, or biofuel industries; the extraction from industrial biowastes such as blood, bones, feathers, wool, hair, nails, etc., from poultry or cattle slaughterhouses; or microalgae from sewage plants [20][21]. However, the commercial use of protein-based bioplastics in 2020 is still residual (with an output lower than 30 kt) as compared to other agropolymers, particularly starch which accounts for almost 400 kt in 2020 [5]. Some authors have indicated that plastics production from proteins is economically feasible, reducing the wastes associated with industrial products [22].

As for the portfolio of bioplastic applications, food packaging remains the widest segment of the whole bioplastic family, with an output of almost 1 Mt in 2020, representing nearly half of the total bioplastics market. The other half is largely diversified finding applications as consumer goods, or in the textile, agriculture, automotive, and construction field, among others [5]. In particular, protein-based bioplastics may also accomplish some of those applications, mainly in the fields of food packaging and plastics for agriculture. Moreover, they may also be used in more specific applications, such as in the development of absorbent and superabsorbent materials, in the controlled release of active agents (e.g., drugs, antimicrobial agents, nutrients, etc.), or biomedical applications (e.g., as scaffolds for tissue engineering) [23]. Therefore, despite the many advantages associated with the use of protein as bioplastics for a wide variety of applications, its high potential for the replacement of conventional plastics has not yet been sufficiently explored [20].

This review is focused on the potentials of protein co-products of the agri-food industry or protein fractions extracted from agri-food industrial biowastes, as well as their applications as substitutes for conventional non-biodegradable fossil-based plastics. The characteristic of these protein-based materials must be analyzed to assess the functionality required for each application. These properties can be typically divided into mechanical properties, thermal properties, and optical properties, correlating them to the microscopic (even molecular) structure of the materials [24].

2. Proteins from Industrial Biowastes and Co-Products

Every year, around one third of all food produced worldwide, is either lost or wasted [25]. In Europe, that amount is reduced to one fifth, being 19% obtained from food processing and 11% from primary production [12]. Food biowaste is mainly composed of carbohydrates, proteins, lipids, and other compounds with great potential for high-value applications [13]. In this section, the main protein-rich biowastes and co-products from the agri-food industry that have been used in the development of plastic materials are presented. It should be highlighted that depending on the application pursued, proteins should be previously extracted and/or concentrated from the biowaste. Extraction can be carried out either through dry (e.g., air classification) or non-dry (e.g., chemical treatment) conditions. Among the concentration procedures for obtaining protein concentrates or isolates are isoelectric precipitation or ultrafiltration. These preparation techniques are outside of the scope of this study, and readers interested in their description are referred to a recent review on this topic [26].

3. Processing of bio-based materials

The production of biodegradable materials is one of the most promising and studied pathways to handle the extremely high amount of biowastes and byproducts that the agri-food industry produces every year [27][28][29][30][31][32]. In this sense, the processing techniques and parameters selected strongly influence the end-use of the material developed. Commonly, these new materials are processed by traditional techniques used for synthetic plastic. However, a specific redesign is needed since these green materials require a different range of processing parameters due to their different composition and properties [33] which would influence their final characteristics, which definitely should be different from those of common synthetic materials [34][35].
The processability of a protein-based raw material is typically achieved either by its solubilization in an adequate solvent followed by a wet technique (casting or electrospinning) [36][37][38] or by a dry technique (e.g., extrusion and injection molding), which previously requires its blending with a low-molecular-weight component acting as plasticizer [39]. In the latter case, the plasticizer content is important for optimum control of the processing parameters, which are crucial to modulate the final properties of the materials. Furthermore, the amount of plasticizer alters the glass-transition temperature (Tg), a key processing parameter to consider during its processing [40][41]. The most extensively reported techniques employed in the production of protein based-materials are described in the following subsections: compression molding, injection molding, extrusion, three-dimensional (3D) printing casting, and electrospinning.

4. Characterization of protein-based materials

Any material processed for any purpose (e.g., packaging, coating, agricultural) must reach some specific characteristics to properly provide the functionality required. Thus, the mechanical properties, the thermal behavior and/or the optical properties of these materials, should be controlled to meet the requirements of their final use. Characterization techniques quantify the macroscopic parameters, relating them to the microscopic (even molecular) structure of the materials. The most important characterization techniques are explained in the following sub-sections.

5. Applications of protein-based bioplastics

The main agri-food industrial biowastes and co-products for bioplastic applications has been described in the previous section. Food biowastes can be used for the production of biofuels [42], but the present review focuses on their application in the field of greener materials, which has been extensively studied but is less exploited commercially, especially the protein fraction. The selection of a suitable biopolymer source is key in the development of any final product with a particular application, which may be chosen based not only on its processing suitability but also on consumer requirements. For instance, animal proteins are commonly rejected in cosmetics, despite being widely accepted in agricultural applications [43]. Moreover, the design and development of bioplastic materials need to bear in mind the accordance between service conditions and the final mechanical and functional properties of the material developed. Although many researchers focus on the mechanical properties of bio-based bioplastics, many applications (i.e., superabsorbent, drug delivery, controlled release, etc.) do not require excellent mechanical properties for their final usage [18][28]. Some critical requirements are demanded for these bio-based materials when used in food applications. For instance, food quality and safety during storage should not be compromised. Moreover, extended shelf-life and a reduced permeability to volatile compounds (i.e., oxygen and moisture) are also pursued [44]. This section summarizes the main applications for the agri-food industry biowastes whose end-use can be linked to the goals of the bioplastic industry. Moreover, this section also addresses the requirements of these bio-based materials for certain applications.

6. Future Trends

Findings gathered in the present review put into focus the wide versatility of bioplastics manufactured from agri-food industrial biowastes or co-products, although the limits for their applicability are still far from being fully explored by the scientific community. In the relatively near future, conventional plastics will disappear in single-use applications, following the European strategy for plastics in a circular economy, which aims to transform the way plastic products are designed, used, produced, and recycled in the European Union. Most current applications are focused on the use of lignocellulose, starch, or fats from food biowaste, and the protein fraction is mostly relegated to low-value applications (e.g., animal food). However, as highlighted in the several applications described above, there is a solid scientific ground to industrially exploit those protein-rich biowastes and co-products. Techniques like electrospinning or 3D-printing have yet to further develop their potential to do so, and proteins which are noncompetitive with the agri-food industry, such as rapeseed or keratin, may find a privileged position. However, the excess of co-products that are only minimally used by the agri-food industry despite being edible, such as blood from the meat industry, should be better employed in applications like those herein presented, in agreement with a circular economy. When bioplastics generated from biowastes and co-products such as those herein indicated are competitive, the laws of supply and demand will help to modulate their use.

References

  1. Fernández-Espada, L.; Bengoechea, C.; Sandía, J.A.A.; Cordobés, F.; Guerrero, A. Development of novel soy-protein-based superabsorbent matrixes through the addition of salts. J. Appl. Polym. Sci. 2019, 136, 47012.
  2. Álvarez-Castillo, E.; Bengoechea, C.; Rodríguez, N.; Guerrero, A. Development of green superabsorbent materials from a by-product of the meat industry. J. Clean. Prod. 2019, 223, 651–661.
  3. Gómez-Heincke, D.; Martínez, I.; Stading, M.; Gallegos, C.; Partal, P. Improvement of mechanical and water absorption properties of plant protein based bioplastics. Food Hydrocoll. 2017, 73, 21–29.
  4. Perez, V.; Felix, M.; Romero, A.; Guerrero, A. Characterization of pea protein-based bioplastics processed by injection moulding. Food Bioprod. Process. 2016, 97, 100–108.
  5. Nadaud, P.; Krochta, J.M. Water vapor permeability, solubility, and tensile properties of heat-denatured. Food Sci. 1999, 64, 1034–1037.
  6. Capezza, A.J.; Glad, D.; Özeren, H.D.; Newson, W.R.; Olsson, R.T.; Johansson, E.; Hedenqvist, M.S. Novel sustainable superabsorbents: A one-pot method for functionalization of side-stream potato proteins. ACS Sustain. Chem. Eng. 2019.
  7. Ashter, S.A. 7–Processing biodegradable polymers. In Plastics Design Library; Ashter, S.A., Ed.; William Andrew Publishing: Norwich, NY, USA, 2016; pp. 179–209. ISBN 978-0-323-39396-6.
  8. Lukubira, S.; Ogale, A.A. Thermal processing and properties of bioplastic sheets derived from meat and bone meal. J. Appl. Polym. Sci. 2013, 130, 256–263.
  9. Martin-Alfonso, J.E.; Felix, M.; Romero, A.; Guerrero, A.; Martín-Alfonso, J.E.; Félix, M.; Romero, A.; Guerrero, A. Development of new albumen based biocomposites formulations by injection moulding using chitosan as physicochemical modifier additive. Compos. Part B Eng. 2014, 61, 275–281.
  10. Gómez-Estaca, J.; Gavara, R.; Catalá, R.; Hernández-Muñoz, P. The potential of proteins for producing food packaging materials: A review. Packag. Technol. Sci. 2016, 29, 203–224.
  11. Krochta, J.M.; Hernández-Izquierdo, V.M. Thermoplastic processing of proteins for film formation. J. Food Sci. 2008, 73, R30–R39.
  12. Budhavaram, N.K.; Miller, J.A.; Shen, Y.; Barone, J.R. Protein substitution affects glass transition temperature and thermal stability. J. Agric. Food Chem. 2010, 58, 9549–9555.
  13. di Gioia, L.; Guilbert, S. Corn protein-based thermoplastic resins: Effect of some polar and amphiphilic plasticizers. J. Agric. Food Chem. 1999, 47, 1254–1261.
  14. Uitto, J.M.; Verbeek, C.J.R. The role of phase separation in determining the glass transition behaviour of thermally aggregated protein-based thermoplastics. Polym. Test. 2019, 76, 119–126.
  15. Masavang, S.; Roudaut, G.; Champion, D. Identification of complex glass transition phenomena by DSC in expanded cereal-based food extrudates: Impact of plasticization by water and sucrose. J. Food Eng. 2019, 245, 43–52.
  16. Karmee, S.K.; Lin, C.S.K. Valorisation of food waste to biofuel: Current trends and technological challenges. Sustain. Chem. Process. 2014, 2, 22.
  17. Secchi, G. Role of protein in cosmetics. Clin. Dermatol. 2008, 26, 321–325.
  18. Fernández-Espada, L.; Bengoechea, C.; Cordobés, F.; Guerrero, A. Thermomechanical properties and water uptake capacity of soy protein-based bioplastics processed by injection molding. J. Appl. Polym. Sci. 2016, 133, 1–10.
  19. Bradley, E.L.; Castle, L.; Chaudhry, Q. Applications of nanomaterials in food packaging with a consideration of opportunities for developing countries. Trends Food Sci. Technol. 2011, 22, 604–610.
  20. Reichert, C.L.; Bugnicourt, E.; Coltelli, M.-B.; Cinelli, P.; Lazzeri, A.; Canesi, I.; Braca, F.; Martínez, B.M.; Alonso, R.; Agostinis, L.; et al. Bio-based packaging: Materials, modifications, industrial applications and sustainability. Polymers 2020, 12, 1558.
  21. Silviana, S.; Rahayu, P. Central composite design for optimization of starch-based bioplastic with bamboo microfibrillated cellulose as reinforcement assisted by potassium chloride. J. Phys. Conf. Ser. 2019, 1295.
  22. Chalermthai, B.; Ashraf, M.T.; Bastidas-Oyanedel, J.-R.; Olsen, B.D.; Schmidt, J.E.; Taher, H. Techno-economic assessment of whey protein-based plastic production from a co-polymerization process. Polymers 2020, 12, 847.
  23. Mostafa, N.A.; Farag, A.A.; Abo-dief, H.M.; Tayeb, A.M. Production of biodegradable plastic from agricultural wastes. Arab. J. Chem. 2014, 4–11.
  24. Hunt, B.J.; James, M.I. Polymer Characterisation; Springer: Amsterdam, The Netherlands, 2012; ISBN 9789401121606.
  25. Stenmarck, A.; Jensen, C.; Quested, T.; Moates, G. Estimates of European Food Waste Levels; FUSIONS EU: Stockholm, Sweden, 2016; ISBN 978-91-88319-01-2.
  26. del Mar Contreras, M.; Lama-Muñoz, A.; Manuel Gutiérrez-Pérez, J.; Espínola, F.; Moya, M.; Castro, E. Protein extraction from agri-food residues for integration in biorefinery: Potential techniques and current status. Bioresour. Technol. 2019, 280, 459–477.
More
© Text is available under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/)
ScholarVision Creations
Feedback