Development and Valuation of Novel PLA-Based Biodegradable Packaging Materials Complemented with Food Waste of Plant and Animal Origin for Shelf-Life Extension of Selected Foods: Trends and Challenges

Abstract

Food waste and food waste by-products have gained considerable attention in recent years. Based on the principles of circular economy, these materials can be used for the preparation of novel and biodegradable packaging materials for food preservation. Among the matrices that have been well exploited, poly-lactic acid (PLA) comprises a key material to be fortified with food waste by-products, as shown by numerous studies in the recent literature. In this context, the aim of the present review was to provide an overview of the literature on the most recent trends in the use of PLA and food waste by-products to prepare films for the shelf-life extension of foods of animal or plant origin. The results showed that the use of PLA packaging films fortified with food waste by-products of plant or animal origin has greatly expanded in the last 20 years. The application of these novel packaging materials to foods has led to considerable shelf-life extension and stability. However, there is still a gap in the use of specific food waste by-products of plant origin, such as peels, seeds, or gels (i.e., onion peels, grape seed extract, grape pomace, prickly pear cladode gel) or animal food waste by-products (i.e., whey, collagen, gelatin), to prepare PLA-based packaging films. The present review, which comprises the thematic issue of an ongoing doctoral study, examines trends and challenges with regard to this topic that have not been extensively studied.

1. Introduction

Food waste is a serious concern that has grown exponentially in recent years, as it has been reported that more than 50% of plant products, such as fruits and vegetables, are lost or wasted from post-harvesting to consumer-end processes. Also, plant-based by-products are wasted after consuming the main parts of fruit. Some typical examples of these by-products are seeds, peels, fruit pomace, and some fruits or vegetables that lack the required sensory criteria, such as perfect shape or color, and thus are not acceptable to consumers [1]. Most plant-based by-products consist of essential proteins, polysaccharides, organic acids, lipids, and essential oils and can be used as additives to create packaging materials with better physicochemical and biochemical properties [2]. It is well known that biodegradable packaging materials, such as PLA, have poor mechanical properties, thermal stability, and sealability. Different studies that used lime peel [3], pomegranate peel [4], plum peel [5], and grapefruit seed extracts [6] as additives in biodegradable packaging materials found improvements in their capacity as barriers to water and oxygen, along with mechanical properties, while they had antioxidant and antimicrobial activity.

Other fruit by-products are peels from apples, peaches, onions, citrus fruits, and blueberries [2]. The by-products of these fruits contain considerable amounts of cellulose, a polysaccharide that can improve the oxygen barrier and wettability properties of PLA films [7]. Moreover, wine by-products constitute a wide range of food waste, with about 20 million tons of grape pomace generated each year [8]. Wine by-products contain bioactive compounds, such as polyphenols, pigments, minerals, and fibers, which provide health effects and protection against chronic disorders such as diabetes, atherosclerosis, hypertension, cancer, and obesity [8,9]. Their incorporation in biodegradable packaging materials could lead to alternative methods of winery waste valorization and be a solution to the disposal problems of farmers [10]. Overall, food waste utilization is growing exponentially nowadays, and we should focus on newly developed techniques to combine biodegradable and sustainable food packaging with food waste products.

PLA (poly-lactic acid) is a synthetic biopolymer produced by lactic acid monomers from starch or other products rich in carbohydrates (corn, sugarcane, wheat) through fermentation and polymerization [11,12]. Some of PLA’s features and advantages are its biodegradability, high mechanical resistance, and nontoxicity, serving as a barrier to undesirable flavor and odor changes in foodstuffs, low carbon emissions, and low production waste [11]. The disadvantages and limitations of PLA in terms of its use as a food packaging material are its low heat resistance capacity, its weakness as a gas barrier, and its high brittleness, along with high cost due to its difficult and low production worldwide [10,11,13,14]. These are some of the reasons that amplify the importance of food waste utilization and incorporation in PLA, as there have been various efforts in the literature to improve PLA’s chemical and physical properties using nanofillers, such as plasticizers, nano-additives, silica, and carbon nanotubes [11,15,16], for the shelf-life extension of foods [17]. Some other features and benefits of PLA are that it saves energy and reduces the volume of landfills, while it can be used to create hybrid and compostable plastic–paper packaging, along with improvements in its physical properties using the aforementioned treatments for different material modifications [18,19]. PLA has been approved by the United States Food and Drug Administration (FDA) as a safe packaging material for food applications and has been classified as generally recognized as safe (GRAS) [18,20]. Additionally, PLA is the most widely produced biopolymer at the moment, with about 140,000 tons every year, and this is expected to rise by 30% next year, making PLA the most widely used biodegradable material in the food packaging industry [18].

The definition published by the European Bioplastic Organization in 2020 [21] of the necessary conditions that a plastic must have to be defined as bioplastic is that it is bio-based, which means that it is derived partly from biomass, or it is biodegradable, or that it is both [22]. Moreover, there is an increased public awareness of the environmental problems and challenges that must be faced to reduce plastic materials and improve sustainability, thus driving biodegradable and bio-based packaging material development [22]. In 2018, for the first time, the European Commission published its aims and scope for single-use plastics in terms of reducing the impact and volume of certain plastics on the environment, followed by the first directive in 2019 and many corrections and decisions until late 2023. The 10 materials that were included in the directive were the following: (i) plastic bags; (ii) wet wipes and sanitary items; (iii) cigarette butts; (iv) plastic bags; (v) cups for beverages; (vi) beverage containers; (vii) food containers; (viii) cotton bud sticks; (ix) cutlery, plates, straws, and stirrers; and (x) balloons and sticks for balloons. These items, along with their measures, were incorporated in the directive as some of the items that will have the most effective results, but also are the 10 most found items on the European beaches, highlighting the importance of these measures. Also, these measures are applied to food and beverage containers that are made of expanded polystyrene and products made of oxo-degradable plastics. Furthermore, the European Union (EU) has focused on the limitation of other single-used plastics, through some awareness-raising measures, design requirements on bottles, such as the connection of cups to bottles, and the informing of consumers about plastic content and recycling through the labeling. Finally, the specific targets of the European Union are the collection separation of 77% of plastic bottles by 2025, increasing to 90% by 2029, and the incorporation of 25% recycled plastic in PET bottles used in beverages starting in 2025, increasing to 30% for all plastic beverage bottles after 2030 [23]. Also, PET has been extensively used in many applications including food and beverages due to its low cost [24]. However, of around 70 million tons of PET produced worldwide, only 28.4% is recycled, while PET waste management includes its incineration, chemical pyrolysis, and landfill disposal [24], causing extensive environmental pollution. These measures will lead to an exponential growth of PLA utilization as a food packaging material in the following years, as currently, only about 1% of the 386 million tons of plastic that are produced around the world is bio-based or biodegradable [25]. From 2000 until now, the research and publications concerning PLA also had exponential growth, showing the trend in research nowadays and the importance of developing biodegradable and sustainable food packaging materials. PLA’s use as a food packaging material is limited now due to the laws of some countries for compostable food packaging [26]. Starbucks and McDonald’s use coated paper cups made with Ingeo PLA in some countries, while at the Olympic Games of Paris 2024, near the Eiffel Tower, people could drink beer that was offered in PLA cups [26]. These are the occasions that PLA has been used as a food packaging material in the market. Considering the aforementioned information about PLA, it has been carefully chosen as the research object for this doctoral thesis due to its trendiness, as well as for the trends of the EU-launched directives about biodegradable packaging materials, showing that PLA is about to be used at the earliest. Figure 1 shows the relevant information about the use of PLA in research studies and its comparison with other biopolymers, according to the Scopus database. It is evident that PLA holds the second position after the widely used chitosan.

Supplementary Figure S1 provides the research articles that have been published about PLA and can be found in the Google Scholar database for the period 2000–2024. It is remarkable that the relevant studies increased exponentially and launched up, especially after 2015.

According to Wellenreuther et al. [25], despite the research interest in PLA as a thermoplastic material and its features, there is still a lack of research reflecting PLA cost analysis or techno-economic analysis. Overall, there was an increase in bioplastic production from 2000, from 2.11 million tons to 2.87 million tons, to 2025. This should lead to PLA cost reduction, because of rivalry [21]. Wellenreuther et al. [25] stated that PLA cost depends on the raw materials used (corn starch, corn grain, cassava starch, etc.), along with the energy requirements, chemicals, distribution, and sales. Several studies [27,28,29,30,31] analyzed the costs of PLA production, considering the processes and feedstock. It is remarkable that feedstock is a variable that plays a catalytic role in PLA cost, along with the performance and quantity of PLA that can be produced. PLA cost minimum values in EUR per ton depending on the feedstock are as follows: (i) corn grain: 798 EUR/t, (ii) triticale: 861 EUR/t, (iii) potato: 1710 EUR/t, (iv) cassava: 2279 EUR/t, and (v) food waste 3365 EUR/t, and they are represented comparatively in Figure 2.

Considering the abovementioned information, the present review article focuses on the utilization of certain food waste by-products of plant and animal origin and their prospects to be used as food packaging materials by the food industry. Moreover, this review critically assesses the development of PLA films with improved mechanical and oxygen barrier properties, along with antioxidant and antibacterial activity that could be implemented for the shelf-life extension of different foods. The subject of this review article constitutes an ongoing doctoral thesis, and moreover, it compares the results of different studies that developed similar packaging materials, biodegradable or not, and represents the trends and challenges of these efforts. To our knowledge, limited hypotheses are available in the literature with this overall concept, and this constitutes the novelty of the present review article.

2. Food Waste By-Products of Plant Origin

2.1. Onion By-Products

Onion and garlic are some of the most consumable foods around the world. Onion (Allium Cepa L.) peels result in a huge amount of waste that is discarded, generating about 300–500 kg of onion waste per day in India [32]. The production of onions has increased by 30% in recent years, thus generating increased waste from damaged bulbs, skin, peels, roots, and flowers [33]. The disposal of onion waste has certain problems due to its strong aroma and toxicity, its high concentration of sulfur compounds, and its high moisture content. So, the researchers are urged to take advantage of onion waste with the extraction of its bioactive compounds and the production of biopolymers to develop packaging materials [33]. It has been documented that onion peels contain flavonoids that are responsible for antimicrobial, antioxidant, and anti-inflammatory properties [32]. Also, red onion peels contain anthocyanins, a flavonoid group responsible for the red/purple color of onion skin [34]. Dietary flavonoids have an important role in human health, providing antioxidant, anti-inflammatory, anticancer, antithrombotic, and antibacterial effects [34]. Due to these health benefits, many studies tried to extract polyphenols and anthocyanins from onion peels with different methods to obtain high yield and stability because of the unstable nature of anthocyanins and their sensitivity in oxidation [35]. The properties of these peels can be used to develop flexible biodegradable films, friendly to the environment, with antioxidant and antimicrobial properties that can contribute to the shelf-life extension of different foods [32]. Additionally, onion peels consist of proteins, total dietary fibers, minerals, and carbohydrates, especially polysaccharides that help in the development of flexible biodegradable and edible packaging materials [36]. Red onion peels are also rich in various bioactive compounds and phytochemicals, such as tannins, ferulic acid, quercetin, kaempferol, and coumaric acid, highlighting the importance of the utilization of these peels [36]. Furthermore, onion peels are rich in lignocellulosic materials that help in the development of packaging materials with better mechanical properties and permeability to oxygen and water and improve the shelf-life of different food products after application. It is important to highlight that onion peels contain about 31.41% cellulose, 2.57% hemicellulose, and 6.05% lignin, along with high amounts of sugars and polysaccharides [33]. One of the most well-known methods for developing biodegradable films is the solution method. In this method, the base biopolymer is dissolved into a solvent (PLA is soluble in chlorinated hydrocarbons, such as chloroform), and then the antioxidant by-product is added. If there is a good dispersion of biopolymer/by-product in the mixture, then the final form of film has the expected properties (antioxidant, antimicrobial, and specific color) [37,38].

PLA is a polymer obtained from many lactic monomers with different methods. The lactic monomer is produced by agricultural waste, such as starch, soy protein, corn, and sugar extraction [39]. Recently, researchers studied the application of red onion peels and red onion peel extracts in biodegradable packaging materials like PLA (poly lactic acid) and carboxymethyl cellulose [32,40]. The addition of onion peel extract and onion peel powder on films based on carboxymethyl cellulose provided strength to the film structure and decreased water vapor permeability. Also, the fabrication of antioxidants from onion peels into the film resulted in more stable release and better antioxidant activity, while SEM images showed smoother and uniform surfaces on the fabricated films [40]. Acylated onion peel powder incorporated in PLA films resulted in improved hydrophobic properties that led to better water vapor permeability, while the films had 99.65% antimicrobial activity against Staphylococcus aureus and Escherichia coli bacteria, in comparison with control PLA films that had 0%. These results were mainly attributed to the presence of flavonoids and polyphenols in onion peels [32]. In another study, researchers tried to develop films based on sodium alginate with glycerol as a plasticizer, enriched with purple onion peel extracts in different concentrations (0, 10, 20, 30%), resulting in better optical and functional properties, but decreased mechanical and water barrier properties [41]. These results show that onion peel extract is probably not so suitable for improving sodium alginate film properties. In conclusion, to our knowledge, there is a lack of research in the recent bibliography that incorporates onion by-products in PLA-based biodegradable films, showing the importance of this field of study.

Table 1. Food waste by-products incorporated in biodegradable matrices along with their mechanical, biochemical, antibacterial, and sensory properties.

Matrix	Food Waste	Mechanical Properties	Biochemical/Antibacterial/Sensory Properties	References
PLA	Onion peel	TS ↑	AA ↑ antibacterial	[32]
Carboxymethyl cellulose	Onion peel	Water barrier ↓ moisture and solubility ↓	Antioxidant activity ↑	[40]
Sodium alginate	Onion peel extract	TS ↓ EB ↓ water barrier ↑ solubility ↓	TPC ↑ antioxidant activity ↑ no antibacterial properties (E. coli and S. Aureus)	[41]
PLA	Red grape pomace extract	TS ↓ elastic modulus ↓	Antioxidant activity ↑ antibacterial	[42]
PLA	Tempranillo grape pomace extract	-	Antioxidant activity ↑	[43]
PLA	Grape seed extract	EB ↑	Antibacterial	[44]
PLA	Grapevine cane extract	Elastic modulus ↓TS ↓ Water barrier ↑	Antifungal	[45]
Chitosan	Prickly pear cladode gel	-	Cherry shelf-life extension, organoleptic ↑	[46]
PLA	Whey	EB ↓ elastic modulus ↑ oxygen barrier ↑ water barrier ↓	-	[47]
Whey	Whey with ascorbic acid	UV barrier ↑ water barrier ↓ elastic modulus ↓ TS ↓ EB ↑	-	[48]
Whey	Pineapple crown leaf cellulose	Solubility ↓ TS ↑EB ↓ Moisture absorption ↓	-	[49]
Chitosan	Collagen	Solubility ↓	Antifungal and antibacterial	[50]
Sodium alginate	Collagen	Water barrier ↑	-	[51]
PLA	Gelatin	TS ↓ EB ↑ water barrier ↓ oxygen barrier ↑	-	[52]

TS: tensile strength, EB: elongation at break, UV: ultraviolet, AA: antioxidant activity, TPC: total phenolic content, ↑: improved, ↓: reduced.

shows different food waste by-products incorporated in various biodegradable matrices along with their mechanical and physicochemical properties.

2.2. Winery By-Products

Grapes (Vitis vinifera) have an important role in the economy of many countries, especially around the Mediterranean zone. China is the global leader in grape production, with around 10,800 thousand metric tons of grapes in the 2019/2020 harvesting season [53]. Raw grapes consist of 80.54% water, 18.1% carbohydrates, and 0.72% proteins [54]. The high content of sugars they contain plays a significant role in the completion of the alcoholic fermentation of grapes to produce wine. After the harvesting season between late summer and November, red grapes are picked up and crushed to release the juice. Then, they are subjected to the fermentation stage where grape juice with all the solids that grapes consist of (seeds, peels, and stalks) is fermented, with the addition of yeast (Saccharomyces cerevisiae), to produce alcohol through biochemical processes. Five to seven days later, the fermentation stage has been completed, and grapes are ready to be pressed to extract the juice, separating the seeds, peels, and stalks [55]. Winemakers try to reuse the grape pomace in sustainable ways as animal feed or fertilizer [56]. In Italy, France, Greece, and Spain, wine waste is utilized as land-spread material and animal feed, or it is handled by incineration [10]. Grape pomace is obtained in tons during wine production and is rich in bioactive compounds that exhibit antioxidant, anti-inflammatory, anticancer, and cardioprotective properties, and researchers have extensively tried to develop extraction techniques to recover these phytochemicals [57]. Some groups of bioactive compounds that can be found in grapes and wine are phenolic acids such as hydroxycinnamic and hydroxybenzoic acids, flavonoids like catechin, and anthocyanins and procyanidins [57]. More specifically, the grape skins of red varieties are rich in anthocyanins, flavanols, hydroxycinnamic acids, and flavonol glycosides, while grape seeds contain high amounts of gallic acid and flavanols [58]. A previous study in 2006 [59] compared the polyphenols found in different red and white grape varieties with high-performance liquid chromatography (HPLC). The authors reported that grape seeds consist almost exclusively of flava-3-ols, with gallic acid and protocatechuic acid being in lower concentrations. On the other hand, red grape skins resulted in significant quantities of quercetin glycosides in Merlot and Shiraz varieties, while grape skins in general contained flava-3-ols and different phenolic acids such as caffeic, coumaric, and ferulic acid. Another notable ability of grape pomace is its usage as a preservative to prevent lipid oxidation and suppress the microbiological growth of some bacterial strains such as Escherichia coli, Staphylococcus aureus, and Streptococcus mutans, also providing antitumor activity and preservation against chronic diseases [57]. Figure 3 represents the utilization of grapes in wine and grape pomace that has considerable antioxidant activity based on its bioactive compounds.

The abovementioned features of grape pomace can be utilized to develop novel biodegradable packaging materials with improved mechanical properties and antimicrobial activities to extend the shelf-life of different foods. PLA is a biodegradable material that has had high interest in the biomedical industry in the last few decades due to its great performance in the development of active packaging materials that are friendly to the environment and extend the shelf-life of selected foods [42]. Researchers tried to take advantage of grape pomace properties and develop PLA films fabricated with winery by-products. Bruna et al. [42] developed PLA films fabricated with grape pomace from red grape varieties at different extrusion temperatures, and the prepared films had improved mechanical properties and antioxidant activity. Furthermore, these biocomposites decreased the microbial growth of E. coli and L. innocua, proving the appropriateness of these packaging materials. Similarly, in the study of Verano-Naranjo et al. [43], grape pomace extracts were prepared with two different solvents (ethanol and aqueous ethanol) to identify and quantify the phytochemical compounds of the grape pomace. Among the studied parameters, antioxidant activity and total phenolic composition were determined with ultra-high-pressure liquid chromatography–electrospray ionization time-of-flight mass spectrometry (UHPLC-ESI-ToF-MS) analysis. Continuously, the anti-inflammatory and antimicrobial capacity of these extracts was determined, before the supplementation of PLA film with these two extracts (ethanolic and hydroethanolic, respectively). In comparison with the previously mentioned constituents of grape pomace (i.e., skins, seeds), different anthocyanins were identified (i.e., malvidin 3-O-glucoside, delphinidin-3-O-glucoside, cyanidin-3-O-glucoside, petunidin-3-O-glucoside, etc.), along with flavanols (i.e., procyanidins and catechin) and flavonols (i.e., quercetin and kaempferol glycosides) in various concentrations. In conclusion, PLA films complemented with grape pomace extracts had improved antioxidant activity due to the better swelling effect of PLA with ethanol. In a previous study, Gómez [44] prepared PLA films treated with different concentrations of grape seed extract (1% and 5%, respectively). The higher concentration of the extract resulted in worse mechanical properties than the lower, while the antimicrobial activity of those films against various foodborne pathogens (Listeria monocytogenes, Escherichia coli O26, Escherichia coli O157:H7, Salmonella Infantis, and Salmonella Seftenberg) showed notable inhibitory effects [60]. Another study that needs to be highlighted for its novelty is that of Diaz-Galindo et al. [45], where researchers developed PLA films fabricated with grapevine cane extract and studied their properties against food pathogens (Listeria monocytogenes, Pseudomonas aeruginosa, Pectobacterium carotovorum, and Saccharomyces pastorianus). Wood tissues contain bioactive compounds such as flavonoids, phenolic acids, and stilbenes [61]. The main stilbene derivatives are trans-ε-viniferin and trans-resveratrol, so after the permission of the European Union for resveratrol as a novel food ingredient, grapevine canes utilization is important for the food, cosmetic, and pharmaceutical industry [62]. The results of this study were remarkable, showing an increased elongation at break of treated PLA films in comparison with pure PLA. Additionally, the water vapor barrier properties of these films were improved by 55% compared to PLA. Finally, PLA films with grapevine cane extracts had antifungal and antiadhesion properties, making these packaging materials unique and appropriate for active food packaging with antimicrobial effects.

2.3. Prickly Pear Cladodes

Opuntia ficus-indica L. is a plant that belongs to the Cactaceae family and Opuntia genus. The country of its origin is Mexico, but it grows in different countries with similar climatic conditions, such as Australia, countries in South and Central America, and the Mediterranean countries [63]. More specifically, in Greece, Opuntia ficus indica L. mainly grows in Central and Western Greece, Peloponnese, and Crete, areas with a warm climate. The most typical hybrid varieties are Agave Americana, Santa Ynez, Ellisiana, Sanguigna, and Sulfarina [64]. In these countries, Opuntia’s fruits are consumed widely, given their antioxidant activity, betalains, ascorbic acid, and flavonoid contents [65]. Prickly pear juice also contains high amounts of minerals such as calcium, potassium, and magnesium, along with terpenoids (dl-Limonene) [66]. In addition, the pulp waste of prickly pear fruits has been exhaustively used for the preparation of jams and other candies or even for the preparation of bio-functional alcoholic beverages complemented with honey [67]. Cladodes are a part of the plant that is not utilized widely, except in some countries (i.e., Mexico), where young cladodes are consumed in salads, soups, snacks, and drinks [68]. The edible portion of cladodes contains a high quantity of dietary fibers, proteins, water, fatty acids, polysaccharides, minerals, and vitamins, along with phytochemical compounds, such as polyphenols and phytosterols that provide antioxidant activity and medical properties [63,68], while cladodes have also been used in forms of agriculture such as animal breeding [69]. The carbohydrates in the cladode cell wall are cellulose (the most dominant ingredient), hemicellulose, and lignin in different concentrations. Moreover, they contain monosaccharides and simple molecules of carbohydrates such as fructose, mannose, arabinose, galacturonic acid, glucose, xylose, and rhamnose [70]. It has been reported that the polysaccharides in prickly pear cladodes could retain water, acting as mucoprotective agents. Also, different low-molecular-weight compounds have been identified, such as lactic acid, the simple molecule that is used for PLA synthesis [71]. Opuntia mucilage can act as a protector against oxidative stress and different stress factors, can hydrate the human skin, and finally, has barrier properties against cutis wounds [71]. In the food industry, prickly pear cladodes can be used as an emulsifier, additive, and edible coating for the shelf-life extension of different products, as reported by Medina-Torres in 2013 [72], where research studies microencapsulated gallic acid, a natural antioxidant, in the nopal mucilage of Opuntia with a spray-drying process. Recently, Christopoulos et al. [46] investigated the effect of chitosan-based edible coatings prepared with extracts from prickly pear cladodes in different concentrations. These edible coatings were applied to cherries, and variables such as weight loss, antioxidant activity, total phenolics and flavonoids, total anthocyanins, and microbial decay were studied. The results showed that during storage, the edible coatings complemented with cladodes extract exhibited no negative effect on cherries, while their quality was improved, and storage life was also extended in comparison to the control edible coatings. Another study showed the chemical, structural, and morphological analysis of the mucilage of a relative species, Opuntia spinulifera [73]. Researchers used a set of instrumental analysis techniques, such as Fourier transform infrared spectrometry (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and nuclear magnetic resonance (NMR) spectroscopy, to identify and confirm the existence of specific chemical constituents. FTIR analysis showed common fingerprints in the carbohydrate and polysaccharide region and the presence of pectin and galactose, while NMR spectra confirmed the existence of saccharide units with α and β configurations. More specifically, ¹H NMR spectra confirmed the presence of polysaccharides due to the signals in specific regions that were attributed to α and β carbons, corresponding to 55 sugar residues such as xylose, rhamnose, and galactose. Moreover, signals identified in a different region were attributed to hydrogen next to a –OH group. In 2016, Lefsih et al. [74] reported that pectin from Opuntia ficus indica is precipitated with ethanol in mucilage samples, explaining its presence. Finally, pectin from prickly pear cladodes mucilage was used for the development of pectin/chitosan biodegradable films and their characterization [75], and some studies proved the effectiveness of prickly pear cladodes as a coating material for the shelf-life extension of strawberries, kiwi, and fig fruit [76,77,78,79]. Also, pectin from different citrus species peel powders was used for the development and characterization of PLA-based films [80]. Overall, to our knowledge, there is a lack of research studies on the development of biodegradable packaging materials with prickly pear cladodes, confirming the novelty of this ongoing doctoral thesis.

3. Food Waste By-Products of Animal Origin

3.1. Whey Protein

In the early stages of cheese making, around 5000 B.C., people were challenged and struggled to utilize secondary products, such as a yellow-green sticky liquid [81]. This liquid by-product from cheese making process is whey. Later in the centuries, with the evolution of sciences such as chemistry, microbiology, and engineering, people managed to utilize whey. Whey consists mainly of 93% water, 0.8% proteins, and 5.1% carbohydrates [82], while the dominant carbohydrate is lactose and the main protein is lactalbumin. The most well-known and noteworthy product that occurs from whey utilization is whey protein. Whey protein is a dietary supplement marketed commonly with health claims and medicinal properties [83]. Athletes consume whey protein as a supplement to improve their muscle mass, body weight, and strength [84], and the results of whey consumption have been widely studied, but there is still a lack of consistency in terms of tests, samples, and protein supplements [85,86]. On the other hand, whey protein contains α-lactoalbumins (α-Ias) and β-lactoglobulins (β-Igs), the peptide derivatives of which possess immense functionalities [86,87,88,89]. Moreover, whey protein contains branched-chain amino acids such as valine, leucine, and isoleucine that play a significant role in neural function and blood glucose homeostasis [90], and cysteine, a necessary amino acid that is responsible for glutathione block building [91]. Whey protein is rich in bioactive peptides that reduce oxidative stress and scavenge free radicals. These properties have been attributed to the endogenous antioxidant enzymes that it contains (catalase, superoxide dismutase, ferroxidase, glutathione peroxidase), along with glutathione [92].

The previously reported functionalities of whey protein forced researchers around the world to develop biodegradable packaging materials fabricated with whey protein and test their properties. The major problem of film development with whey protein layers is their brittleness; as a result, whey protein cannot stand alone as a layer without plasticizers which will work as a crosslink between the layers, as reported previously in numerous studies [93,94,95,96,97,98,99,100,101]. In a previous study, Cinelli et al. [93] developed PLA films coated with whey protein layers and tested their oxygen barrier and mechanical properties. The whey-protein-layered films showed better oxygen permeability in comparison with the control PLA films but were lacking however, in barrier property maintenance. Concerning their mechanical properties, PLA/whey films affected elongation at break and reduced tensile strength and elastic modulus values. However, the findings obtained from this study were still suitable for application in food packaging. Overall, these results were positive, leading to new ecological and cost-effective food packaging materials, while the usage of plasticizers resulted in faster biodegradability [93].

In the following years, whey protein as an additive in biodegradable materials was spread out widely, and in 2022, Kamali et al. [102] developed PLA bilayer films with whey/pullulan in different thickness ratios that contained a Listeria phage and applied them to chicken breasts. Encapsulated packaging materials with phages have been used widely in different studies to reduce the microbial growth of specific pathogens such as Pseudomonas fluorescens [103], Salmonella Typhimurium [104,105], Listeria monocytogenes [106,107], and Escherichia coli [108,109]. In the study of Kamali et al. [102], the results were important, showing not only that the growth of Listeria was inhibited, being affected by A511 phages, but also that the mechanical properties of the films had higher tensile strength and elastic modulus values in combination with the lower water vapor permeability (due to the hydrophobic properties of PLA, although whey protein has hydrophilic properties). It is quite notable that the contact surface of bilayer films plays a significant role in the hydrophilicity or hydrophobicity of the packaging materials, along with their contact angle [110,111].

Moreover, Phupoksakul et al. [47] developed three-layer films of PLA and linear low-density polyethylene (LLDPE) films that had whey protein as the middle layer. Researchers used glycerol as a plasticizer in different ratios for the preparation of the whey protein layer and the corona treatment assay to bond the layers. Corona treatment is a method that changes the surface by discharging plasma and has been used widely for essential oil incorporation in LDPE films [112]. The tensile properties of PLA films were significantly higher than those of LLDPE films, along with higher elastic modulus values. Additionally, PLA films had lower oxygen permeability (OP) values in comparison with LLDPE. Although glycerol has a minor role in oxygen permeability reduction, as reported by some researchers [113,114,115], it is important that a biodegradable packaging material has lower OP values than a common plastic. The sustainable features of PLA films as a green alternative packaging material and their improved oxygen barrier properties can lead to their investigation as shelf-life extenders of oxygen-sensitive dry foods [47].

Over the years, whey protein has not only been used as an additive for synthetic or biodegradable polymers. Etxabide et al. [48] developed active and sustainable whey-protein-based films incorporated with ascorbic acid in different ratios and tested their properties. The findings of this research were remarkable concerning the UV-Vis light barrier properties of whey-protein-based films. The control films without ascorbic acid incorporation presented high barrier properties in the range of 200–400 nm (UV region), due to the high concentration of aromatic amino acids in whey protein, which can absorb UV light [48,116,117], while the incorporation of ascorbic acid extended the absorbance range (200–500 nm). The light barrier properties of these films can lead to application in foods with high lipid concentrations, as they can protect them from lipid peroxidation caused by UV-Vis light [48,118]. Also, incorporated films had higher water vapor values because of the high amount of hydroxyl (OH) groups in ascorbic acid that promote better water vapor diffusion inside the film [119]. The mechanical property tests of these films resulted in significant conclusions concerning their tensile strength, elongation at break, and elastic modulus values. The control whey-protein-based films had higher tensile strength and elastic modulus values, while the higher the concentration of ascorbic acid added, the lower the values of tensile strength and elastic modulus. Control films had a lower elongation at break, while the fabricated films had approximately the same values. These findings lead to a wide range of choices concerning the concentration of ascorbic acid that should be added, depending on the food and purpose of use. With the same reasoning, Fitriani et al. [49] developed whey-protein-based films fabricated with nanocrystalline cellulose isolated from pineapple crown leaf. This research promotes the importance of circular economy and sustainability, as the basic components for developing these films come exclusively from food waste products [120,121]. Different concentrations of nanocrystalline cellulose were encapsulated in whey-protein-based films, and their mechanical properties were improved. More specifically, when a higher concentration of nanocrystalline cellulose was added, the tensile strength values were increased, while elongation at break decreased. These results show that nanocrystalline cellulose hardens whey-protein-based films and offers a variety of choices for our desired properties, depending on the packaged food. Moreover, when the concentration of nanocrystalline cellulose increased, the water solubility of the films decreased, along with moisture absorption. These findings can be attributed to the distribution of nanocrystalline cellulose in the whey protein film, creating functional groups that close the gaps of biopolymer molecules [49,122,123]. Also, these strong structures and bonding provide a lower water solubility, which can also be attributed to the water-resistant characteristics arising from the crystalline area of nanocrystalline cellulose [49,124,125].

In summary, whey protein is a useful and functional tool for developing encapsulated biodegradable polymers or whey-protein-based packaging materials that have specific characteristics. Still, there is a lack of research about packaging materials fabricated with whey protein, and in parallel, there are numerous parameters that should be considered and analyzed to improve their range of applications.

3.2. Fishery By-Products

A large group of living organisms that live in freshwater and marine environments are fishes. Fishes consist of about 34,000 species globally, and they are farmed or caught wild from marine or inland water sources, such as lakes and rivers [126]. Fish and fish by-products play a crucial role in the human diet, especially in Mediterranean countries, where a lot of people raise their income from fishing and selling fish. In addition, fish contain essential unsaturated fatty acids, amino acids, micronutrients, and oils rich in vitamin A, along with eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which make fish healthy foods that act against cardiovascular diseases [126,127,128]. Fish production worldwide was estimated at around 178.5 million tons, concerning aquaculture and capture fisheries, with a rate of increase of 3% until 2020 [129]. According to Samarejeewa et al. [126], in 2020, approximately 89% of fish was edible in good quality, while the other 11% was diverted for feed. Of the total production worldwide, around 40% is wasted as non-edible components [130]. More specifically, around 30% of fish is wasted for quality reasons, while the other 8% is wasted for safety reasons. The products that occur from fish waste are chitin and chitosan, polypeptides, collagen, gelatin, proteins, enzymes, and fish oil [126]. Though fish waste utilization has increased in recent years, the potential remains high due to its inedible parts that can be purchased from industries that produce significant amounts of fish discards [129]. The fish waste parts that occur from industries are bones, skin, head, fins, tails, gut, and liver. Solid fish waste is dangerous if disposed of in landfills, as it is rich in organic content, which is associated with water and land contamination. As detailed in the comprehensive review of Thirukumaran et al. [129], one of the bioactive compounds that occur from the aforementioned parts of fish is gelatin from the skin or inner and outer tunics; it has a wide recovery range of 10.58–43.50% that depends on the fish and antioxidant and antihypertensive properties, and it can be used for functional ingredients in the food industry or for capsule preparation in the pharmaceutical industry [131,132,133]. Moreover, collagen from the skin and body parts of fish can be obtained in a recovery range of 20–33% and also offers antioxidant activity for medical and cosmetic products, along with functional foods [134,135]. Also, fish oil and peptides derived from fish waste possess antioxidant properties and can be utilized by the food or pharmaceutical industries [136,137]. These findings highlight the importance of fish waste utilization.

3.2.1. Collagen

The main fishery by-products that could help in the development of biodegradable packaging materials are collagen and gelatin. Collagen has been reported in earlier years as a biological plastic, in many ways [138]. Its molecules are organized in a precise way, as they are aligned end to end and are polymerized side to side [138]. Recently, collagen that was extracted from cow hide and sodium alginate were used as the base to develop biodegradable packaging materials fabricated with pomegranate peel powder and chitosan, respectively [139]. The results showed that films had improved biodegradability, along with increased mechanical strength, mainly for the film that was fabricated with pomegranate peel powder. Moreover, the films exhibited antimicrobial activity against Escherichia coli and Bacillus cereus, which can be attributed to the antioxidant properties of chitosan [129] and pomegranate peel powder [140]. Concerning collagen from fish, the best extraction methods are acid-soluble collagen (ASC), enzyme-soluble collagen (ESC), ultrasound extraction, Deep Eutectic Solvent (DES), and Supercritical Fluid Extraction (SFE) [141]. Recently, polyglycolic acid (PGA) with lyophilized type I collagen derived from porcine tissue was used for the development of novel nanofiber blends with improved properties for potential biomedical applications [142].

In 2019, Bhuimbar et al. [50] used acid-soluble collagen extraction to extract collagen from fish waste and developed a collagen–chitosan blend as food packaging material. More specifically, the researchers used the skin of Centrolophus niger to extract its collagen, removing the non-collagenous proteins first and characterizing the collagen itself, and later, they developed a collagen–chitosan blend, also incorporated with pomegranate peel powder in different concentrations, as mentioned previously. The blended films were prepared successfully, showing the incorporation features they have, and had also antibacterial activity against some foodborne pathogens, such as Bacillus saprophyticus, Bacillus subtilis, Salmonella typhimurium, and Escherichia coli. These findings are in agreement with the study of Maliha et al. [139], furthermore proving the antibacterial activity of pomegranate peel powder in collagen-based packaging materials. Moreover, in 2021, Júnior et al. [51] developed sustainable and edible food packaging materials with sodium alginate and hydrolyzed collagen in different concentrations. The authors concluded that the higher the concentration of hydrolyzed collagen, the higher the water barrier properties. Also, hydrolyzed collagen increased the thermal stability of the films. According to our literature research and knowledge, there were not any published papers that studied the incorporation of collagen in biopolymer matrices, which creates the basis for further research.

3.2.2. Gelatin

As mentioned previously, gelatin is a fishery by-product that could be a useful tool in the development of biopolymer-based food packaging materials. Gelatin has been studied quite extensively in recent years for its ability to form films with good functional properties that provide protection from oxygen and light and protect foods from drying [143,144]. Moreover, films with gelatin have been found to possess good mechanical properties, but their weakness is their poor water barrier properties and moisture sensitivity, thus providing a limited application range in foods with high moisture content because they may swell or dissolve in contact with water [144,145]. To avoid these issues caused by gelatin’s instability, some researchers tried to develop bilayer films of fish gelatin and PLA, in different thickness ratios [52]. The results showed that bilayer films had lower tensile strength values but higher values of elongation at break in comparison with pure PLA films. More specifically, the bilayer films with the highest ratio of gelatin had the higher elongation at break, which offers a plethora of different ratios to choose from, depending on the food that will be packaged and the properties of the used packaging material. Furthermore, the better oxygen barrier properties provided by the bilayer films with a high gelatin ratio showed a great gap from pure PLA. These findings confirm the abovementioned properties highlighted by Bakry et al. [143] and Sunderman et al. [144]. Lastly, water vapor permeability values were lower in the bilayer films with a high PLA thickness ratio, and pure PLA had the lowest value. As mentioned previously, gelatin films have bad water barrier properties, resulting in swelling or dissolving, making thus these films a bad choice for developing packaging materials for foods with high moisture content [144,145]. UV light barrier properties also increased with the addition of a high ratio of gelatin, which is also a remarkable finding that makes gelatin–PLA bilayer packaging material suitable for biodegradable food packaging.

Later, Nilsuwan et al. [146] evolved their previous work by adding epigallocatechin gallate (EGCG) to a PLA/gelatin bilayer film, as an alternative approach which enhanced the antioxidant activity of the prepared films. The incorporation of EGCG created interactions with gelatin, as first shown by FTIR spectroscopy and then proven by scanning electron microscopy (SEM), resulting in homogeneous structures. The bilayer films had good mechanical properties, along with high UV light barrier ability and good water vapor permeability. Moreover, the results showed that the films had antioxidant activity in the DPPH assay, as EGCG was released properly during 7 days of storage. These findings affected the quality of striped catfish packaged in the bilayer films of gelatin/PLA and incorporated with EGCG in comparison with the control samples that were packaged in LLDPE bags, as these inhibited oxidation based on the use of the thiobarbituric acid reactive substance (TBARS) assay, which is based on the decomposition of peroxides to aldehydes and ketones [147] and provides results commonly expressed as mg malonaldehyde/kg sample. Also, the fatty acid profile of fresh catfish strips on day 0 and day 7 was determined with gas chromatography–flame ionization detector (GC-FID) and confirmed the impact of EGCG bilayer films, showing low chemical changes. Furthermore, EGCG films showed antimicrobial activity [148], which affected the microbiological profile, inhibiting the growth of total viable count (TVC) and psychrophilic bacteria count (PBC). Also, a sensory analysis showed a higher likeability for catfish strips that were packaged in gelatin/PLA bilayer films with EGCG.

Fish by-products constitute a huge food waste problem worldwide. Their utilization is crucial for environmental sustainability and food waste reduction. The isolation of certain bioactive compounds originating from fish by-products could lead to new protocols for developing biopolymers with improved properties, suitable for food packaging. Finally, the incorporation of antioxidant compounds is a challenge that could help in the shelf-life extension of selected foods.

4. Discussion

This literature review article focuses mainly on the utilization of food waste by-products of plant and animal origin and their incorporation in PLA-based packaging materials for the development of novel packaging technology to extend the shelf-life of different foods. After our analysis of the recently published articles and finding of gaps, onion peels, prickly pear cladodes, and grape pomace were selected as the plant-origin by-products to be fabricated in a PLA matrix. These food waste by-products have been the subject of a wide range of research incorporating them in edible and biodegradable packaging materials, as we mentioned before [32,40,41,42,43,44,45,46,72,75], but there is scarce research interest in fabricating these materials in PLA. Moreover, animal-based by-products were selected with the same reasoning, noticing the extensive research interest in their utilization in edible packaging materials [48,49,50,51,139,142] and their incorporation in PLA, mainly as a second layer in bilayer or three-layer films [47,52,93,102,146].

On the other hand, during the preparation of PLA-based films, some problems can be faced, as the solution method for incorporating solid materials and food waste by-products in PLA is unattractive based mainly on (i) the use of organic solvents and (ii) the possibility of contamination due to the possible traces of the solvent [149]. Also, low heat resistance is a common problem when developing PLA porous membranes [150], along with low brittleness and low toughness properties [151]. Finally, the production of PLA membranes with wide-diameter solid materials, such as food waste by-products, and the use of chloroform as a solvent have lower conductivity and low distribution problems [152], thus resulting in the formation of wide gaps in the polymeric matrix that affect the oxygen barrier properties.

The published articles focusing on PLA have increased exponentially after the 2000s, as can be seen in Figure S1, while the European Union announced new directives and laws for biodegradable biopolymer development and petroleum-based plastic use reduction, thus showing the current trend as we mentioned in the Introduction section. PLA is an expensive biopolymer, and its price can be seen in Figure 2, depending on the feedstock that is used to isolate it. Therefore, its use for the preparation of novel packaging materials must be targeted (Table 1) to manage the shelf-life extension of selected foods efficiently. Furthermore, food waste has been a huge problem in recent years, and the global population growth pushes governments to find new functional and sustainable ways to utilize it, and at the same time to reduce it. It is critical to highlight the high content of phytochemical compounds in onion peels and grape pomace that will be utilized and offer antioxidant and antibacterial properties [32,40,42], while prickly pear cladodes contain pectin that will probably affect the mechanical properties of PLA films. In parallel, whey and fishery by-products mainly affect the mechanical properties of PLA films [47,52,93,146], offering a plethora of parameters to be selected, depending, however, on the food to which the film will be applied.

Additionally, there is still work to complete on the utilization of food waste by-products to be used for the commercial production of packaging films. A problem that should be solved is the actual utilization of food waste from industries. The enactment of laws that will obligate the food industries to handle food waste properly, and at the same time to provide processed food waste to packaging industries, for the development of novel packaging materials, will help in the better visualization of the actual food waste amounts. So, there will be no loss. Also, concerning the cost-effectiveness, availability of waste, and the functionalities offered by incorporation in PLA, we believe that onion peels and winery by-products are the most suitable waste materials for practical application and mass production. The availability of onion peels [32] and grape pomace in some countries [53] is huge, while are low in cost as they mainly are wasted or used as animal feed and fertilizer [56]. These parameters constitute a new challenge for our group to develop PLA-based packaging materials (in the near future) with the desired properties in order to apply them in contact with different foods and monitor their shelf-life.

Finally, we must consider that plant-based versus animal-derived food waste by-products have different properties when introduced into a PLA matrix. These properties concern (i) the mechanical, (ii) biochemical, (iii) antibacterial, and (iv) sensorial attributes (Table 1), parameters that should be carefully considered during the development and consolidation of such experiments.

5. Conclusions and Future Perspectives

The results of the present review article showed that research based on PLA packaging materials has exponentially increased in the last 20 years. It is evident from the databases (Scopus and Google Scholar) that research studies on the use of PLA number almost 600,000. PLA packaging materials fortified with waste by-products of plant or animal origin seem to be a promising technology for preparing packaging films that will increase the shelf-life of selected foods and, at the same time, contribute to the reduction in the use of conventional plastics. In parallel, with the use and management of food waste and food waste by-products through a holistic protocol, there is also a decrease in the disposal of these materials into the environment. The latter treatment contributes to a greener and healthier environment for humans. To our knowledge, great efforts on this thematic issue have been carried out at an international level, but there is still space for research on the exploitation of food waste by-products, such as grape pomace, onion peels, pear cladode gels, or fishery by-products, which will be studied in an ongoing doctoral thesis.