Trends Sci. 2025; 22(9): 10415

EOs are volatile, aromatic compounds extracted from various plant parts, including flowers, leaves, fruits, bark, seeds, and roots [1]. They are composed of complex mixtures of bioactive compounds, primarily terpenes (monoterpenes, sesquiterpenes, and their oxygenated derivatives) and phenylpropanoids [2]. Additional components such as alcohols, esters, aldehydes, phenols, ketones, and acids contribute to their unique functionalities [3]. Terpenes, including pinene, limonene, and myrcene, are simple hydrocarbons, while terpenoids represent oxygenated forms, offering enhanced antimicrobial and physiological activities. Specific terpenes such as carvacrol, eugenol, and thymol have demonstrated antibacterial effects by disrupting cellular functions and inhibiting protein and DNA synthesis, making EOs valuable in addressing antibiotic-resistant bacteria [2-4]. Fish and seafood are critical sources of nutrition, providing essential proteins, omega-3 fatty acids, and micronutrients [5]. However, they are highly perishable, with spoilage driven by enzymatic reactions, oxidative processes, and microbial activity. Upon death, aquatic animals undergo biochemical and physical changes such as internal tissue digestion by gastric juices, discoloration, swelling, and softening, which accelerate microbial growth and quality degradation [6,7]. These rapid deteriorative processes cause substantial economic losses and emphasize the need for effective preservation strategies beyond traditional methods. EFCs have emerged as innovative solutions to enhance food preservation while addressing environmental concerns. EFCs are composed of biopolymers like proteins, polysaccharides, and lipids, offering biodegradable alternatives to petroleum-based packaging [8]. They act as physical barriers against environmental factors and, when infused with EOs, enhance functionality by inhibiting microbial growth and lipid oxidation. Several studies have demonstrated the efficacy of EO-enriched coatings in preserving seafood. For example, EOs combined with bacteriocins effectively suppressed Listeria monocytogenes in ready-to-eat seafood products [9]. EO-based vacuum packaging extended the freshness of rainbow trout [10], and chitosan coatings enriched with EOs preserved shrimp and tambaqui fillets under cold or frozen storage conditions [11,12]. This review aims to compile and present current knowledge on the application of EOs in EFCs for seafood preservation. It focuses on the functional roles of different EOs, the performance of various biopolymer matrices, antimicrobial and antioxidant mechanisms, and relevant regulatory considerations. Challenges such as off-flavor formation, EO volatility, and regulatory constraints are also discussed, providing insights for future research and broader commercial applications.

Spoilage mechanisms in seafood and relevance to edible coating application

Lipid oxidation

Lipid oxidation, the primary cause of rancidity in fatty foods, severely impacts seafood quality, leading to undesirable odors, flavors, and nutritional losses. This chemical reaction occurs between oxygen and unsaturated fatty acids, generating unstable fatty acid hydroperoxides. These hydroperoxides decompose into volatile compounds, directly causing rancidity [13]. Several factors influence lipid oxidation, including the type of fatty acids, free fatty acid content, oxygen levels, temperature, water activity, the presence of minerals or metals, antioxidants, light exposure, and radiation [14]. Foods rich in unsaturated fats are particularly susceptible, as oxidation not only causes rancidity but also reduces nutritional quality by degrading essential components such as polyunsaturated fatty acids (PUFA). Building upon this understanding of lipid oxidation, it is important to note the unique composition of fish fats compared to mammalian fats. Fish fats are richer in long-chain fatty acids (14-22 carbon atoms) with 5 or 6 double bonds, making them highly unsaturated [16-17]. In contrast, mammalian fats typically consist of fatty acids with up to 2 double bonds. Essential fatty acids like eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are abundant in fish oil and are crucial for human nutrition. The rate of lipid oxidation varies among anatomical regions of fish. For example, studies on herring have shown that the head region experiences the highest oxidation rates, while internal organs and the abdominal wall oxidize more slowly [18]. This variability is primarily influenced by hemoglobin levels, lipoxygenase activity, and α-tocopherol concentration rather than total lipid or PUFA content. In addition to anatomical factors, processing methods can further accelerate oxidation. For instance, hot air drying of shrimp progressively increases lipid oxidation, leading to the formation of compounds such as 4-hydroxynonenal, a toxic by-product of fatty acid oxidation [19]. Extended drying times exacerbate this effect by promoting free radical formation and accelerating PUFA degradation. Addressing lipid oxidation is critical for maintaining seafood’s sensory quality, nutritional value, and shelf life. Table 1 summarizes the lipid and fatty acid composition across various seafood species, highlighting their vulnerability to oxidative deterioration.

Table 1 Example of lipid and fatty acid composition of fish and seafood.

Proteolytic changes

Proteolytic activity is one of the major factors driving the spoilage of fish and seafood, leading to texture softening, loss of structural integrity, and the development of undesirable odors and flavors. This process involves the enzymatic breakdown of proteins and nitrogenous compounds, both from endogenous and microbial sources. Factors such as processing methods, salting procedures, marination, and brine composition significantly influence the extent of proteolytic changes. After harvest, post-mortem reactions in seafood muscle tissues result in the degradation of proteins and non-protein nitrogen compounds, causing notable changes in color, flavor, and texture. The breakdown of nitrogenous compounds, particularly non-protein compounds, generates unpleasant odors and putrid-smelling by-products, which serve as key spoilage indicators. Understanding these biochemical processes is critical for developing strategies to manage seafood freshness and quality during storage. Enzymatic activity significantly contributes to the degradation of muscle proteins. Endogenous enzymes such as lysosomes, cathepsins, calpains, and collagenases play critical roles in breaking down myofibrillar proteins, which are primarily responsible for maintaining the structural integrity of muscle tissue. These enzymatic actions lead to muscle softening, structural weakening, and a progressive decline in seafood quality after death [1,6,7]. To mitigate these proteolytic changes, frozen storage is commonly employed to inhibit enzymatic activity and microbial growth. Freezing helps preserve aroma, flavor, color, and nutritional value; however, prolonged storage can moderately impact the texture due to protein denaturation and aggregation. These changes occur because protein molecules gradually lose their functional properties during extended freezing periods, thereby affecting overall seafood quality [1,6]. Experimental evidence further illustrates the impact of proteolysis during frozen storage. A study monitoring enzymatic activities, including trypsin, calpain, and catechin, in intact and decapitated shrimp during 120 days of frozen storage revealed critical insights. The results showed that the content of myofibrillar proteins and Ca²⁺-ATPase activity decreased over time in both groups. However, the decline was significantly more pronounced in intact shrimp, as decapitation appeared to inhibit enzymatic activity by preventing the transfer of trypsin enzymes from the shrimp head to the muscle tissue through the first abdominal segment [22,23]. Myofibrillar proteins, such as actin and myosin, are essential for maintaining seafood muscle texture and water-holding capacity. Ca²⁺-ATPase activity is a valuable biochemical marker of freshness and quality, with its reduction signaling ongoing protein degradation. The myofibrillar fragmentation index also demonstrated that decapitated shrimp exhibited less muscle protein dissociation compared to intact shrimp. By limiting the enzymatic action of trypsin, calpain, and catechin, decapitation effectively extended the shelf life and preserved the textural quality of shrimp products. Overall, understanding the enzymatic processes and their effects on muscle proteins is crucial for optimizing seafood storage methods and maintaining quality during extended storage periods. Figure 1 illustrates the typical proteolytic changes observed in fish muscle during postmortem deterioration.

Off-flavor formation

Unpleasant tastes and odors in fish and seafood products are significant challenges for the fishing industry, significantly affecting consumer acceptance and economic viability. These undesirable flavors often result from compounds such as hexanal, heptanal, nonanal, and trimethylamine, which are generated through various biochemical and environmental processes. The disparity in flavor profiles between aquaculture-raised and wild-captured fish further underscores the need for managing odorous volatile compounds to meet consumer preferences and maintain market value [23]. Several factors contribute to developing off-flavors in fish (Figure 2). Environmental conditions, feed composition, and contamination during rearing can lead to undesirable tastes and odors. Post-mortem changes exacerbate these issues, as spoilage processes driven by microbial growth, enzymatic activity, and lipid oxidation produce distinct off-flavors [24]. These mechanisms highlight the importance of understanding the formation and sources of off-flavor compounds to implement effective mitigation strategies in seafood processing. Identifying the causes of undesirable flavors before and after fish death is crucial for the industry to adopt corrective measures, maintain product quality, and ensure consumer satisfaction. Tables 2 and 3 show fish and seafood’s pre-hunting and post-hunting off-flavor compounds.

Figure 1 Proteolytic changes of fish.

Figure 2 A mechanism or reaction of off-flavor formation in seafoods.

Figure 3 Physical and biochemical changes in seafood during storage.

Table 2 Pre-hunting off-flavor in fish and seafood.

Table 3 post-hunting off-flavor in fish and seafood.

K-value

The K-value is a key index used to evaluate the freshness of fish and aquatic animals by measuring the progression of nucleotide degradation post-mortem. It reflects the biochemical changes in fish immediately after death, while endogenous enzymes remain active before significant microbial spoilage occurs [33]. Following the death of fish and aquatic animals, adenosine triphosphate (ATP) in the muscles undergoes enzymatic dephosphorylation, converting into adenosine diphosphate (ADP) and adenosine monophosphate (AMP). Subsequently, deamination transforms AMP into inosine monophosphate (IMP), which occurs rapidly due to enzymatic activity. Over time, microbial enzymes further degrade IMP into hypoxanthine, xanthine, and uric acid, signaling a decline in freshness [34]. The K-value is calculated as the ratio of nucleotide breakdown products (inosine and hypoxanthine) to the total nucleotide pool. A low K-value indicates freshness, whereas a high K-value signifies advanced spoilage.

For example, in studies monitoring rainbow trout (Oncorhynchus mykiss), the initial K-value was approximately 8% but increased to 50% after 24 h of storage and 73% after 28 h, signifying significant freshness loss over time [35]. Temperature plays a critical role in K-value progression. Research on Sebastes thompsoni revealed that refrigeration at 0°C significantly slowed the increase in K-value compared to storage at 10°C, underscoring the importance of precise temperature control during storage [36]. However, inaccuracies in temperature management during transportation often lead to accelerated spoilage. A study on yellow croaker (Pseudosciaena crocea) stored at 5, 10, and 15°C demonstrated that a lower storage temperature (5°C) resulted in a slower K-value increase and extended shelf life. Interestingly, the K-value at 10°C provided a more accurate shelf-life prediction under practical conditions [37]. The relationship between K-value and storage conditions has also been observed in shrimp, such as whiteleg shrimp (Litopenaeus vannamei). The K-value showed a linear correlation with storage time in whole shrimp and shrimp meat stored at 25°C, making it a reliable indicator for tracking freshness loss over extended periods [38]. These findings highlight the utility of the K-value as an essential tool for assessing the quality and shelf life of seafood, with its effectiveness influenced by storage temperature and handling practices.

Microbiological issues

Microorganisms in fish and seafood play both beneficial and detrimental roles, significantly influencing these products’ quality, shelf life, and safety. Beneficial organisms, such as those found in the gastrointestinal tracts of aquatic species like lobsters, include Vibrio, Pseudomonas, Bacillus, Micrococcus, Flavobacterium, Acinetobacter, Aeromonas, Alteromonas, Clostridium, Marinobacter, Pelagibacter, Photobacterium, Psychrobacter, Pseudoalteromonas, Shewanella, and Synechococcus. These microorganisms vary in composition and abundance depending on the environment, and they contribute positively by aiding digestion through the secretion of enzymes like lipase, protease, and cellulase. They also play a role in nutrient absorption, vitamin synthesis, and enhancing host immunity by stimulating immune responses in the gastrointestinal tract [39-41]. However, microorganisms can also play a detrimental role in seafood spoilage. After the organism’s death, biochemical changes in the tissues create an environment conducive to the growth of spoilage bacteria, particularly those in the gums, mucus, and digestive tract. Spoilage microorganisms commonly associated with fish and seafood include Pseudomonas, Acinetobacter, Moraxella, and Flavobacterium. When refrigeration is inadequate or temperatures rise slightly, other bacteria such as Micrococcus, Bacillus, Proteus, Serratia, Sarcina, and Clostridium may also proliferate. These bacteria can hydrolyze seafood proteins via protease, forming ammonia, hydrogen sulfide, organic acids, unpleasant aromas, undesirable tastes, and an unsatisfactory texture [40,41]. Many of these bacteria grow rapidly at room temperature and can even grow to some extent under refrigeration, leading to significant quality degradation [42]. Some microorganisms are linked to specific spoilage phenomena. For example, Bacillus sp. and Acinetobacter sp., in shrimp, produce the enzyme tyrosinase, which triggers oxidation reactions that lead to black spot formation in shrimp [43]. Additionally, certain microbes in seafood pose serious health risks to consumers. Foodborne pathogens, such as bacteria, viruses, or parasites, are responsible for food poisoning [42,43]. They, such as Vibrio vulnificus, Vibrio parahaemolyticus, Vibrio cholerae, Salmonella enterica, Shiga toxin-producing Escherichia coli (STEC), Listeria monocytogenes, and Clostridium botulinum, can cause severe infections or intoxications. Notably, Vibrio vulnificus, Vibrio parahaemolyticus, Vibrio cholerae, Listeria monocytogenes, and Salmonella enterica are associated with severe and potentially fatal outcomes [44]. The scombroid toxin, or histamine poisoning, is another significant health concern linked to consuming scombroid fish species such as tuna, mahi-mahi, and bluefish. Spoilage bacteria producing decarboxylase enzymes convert free histidine in fish tissues into histamine in toxic amounts. Additionally, toxins produced by Salmonella spp. and Clostridium botulinum are highly neurotoxic and linked to numerous outbreaks and illnesses in the United States. Contaminated fish products, especially raw fish like tuna, mahi-mahi, barracuda, and salmon, are familiar sources of these toxins, underscoring the need for stringent microbial control during seafood processing and storage [45]. Table 4 provides the occurrence of spoilage bacteria in seafood products.

Table 4 Occurrence of spoilage bacteria in seafood products.

Physical changes

The physical changes in fish and aquatic animals during storage significantly impact their sensory attributes and consumer acceptance. Among these changes, color alterations are often noticeable and result from various biochemical and enzymatic processes. The oxidation of myoglobin to metmyoglobin, which is brown, is a primary cause of discoloration. Additionally, metmyoglobin acts as a pro-oxidant, accelerating lipid oxidation and contributing to further quality degradation. During cryopreservation, the Maillard reaction, involving reducing sugars and amino acids, can occur due to continued glycolysis even at low temperatures. The Maillard reaction is achieved at any temperature. The lower the temperature, the slower the reaction proceeds [47]. This reaction produces fluorescent intermediates and impacts the appearance of aquatic products [33]. Fish with high-fat content are particularly prone to browning due to interactions between proteins and lipid oxidation products. For instance, unsaturated carbonyl compounds generated from fish oil oxidation can react with proteins, leading to a brown discoloration. Enzymatic reactions also play a critical role in color changes. Polyphenol oxidase (PPO), for example, catalyzes the oxidation of phenolic compounds in the presence of oxygen, leading to melanosis or black spot formation in shrimp. This process involves the hydroxylation of phenols to diphenols and the subsequent oxidation to o-benzoquinones, which polymerize into melanin, reducing product acceptability [48]. Texture changes during storage also serve as indicators of fish quality deterioration. The initial loss of springiness and increased softness resulted from muscle digestion, weakening of connective tissues, and the separation of muscle myofibrils. Over time, these changes are exacerbated by protease enzymes originating from the fish itself and spoilage bacteria. These endogenous and bacterial proteinases progressively break down muscle proteins, leading to a paste-like texture in advanced stages of spoilage [1,6,7]. Figure 3 illustrates the physical and biochemical changes in seafood during storage, including mechanisms of color alteration, texture softening, drip loss, surface dehydration, and ice crystal damage.

EOs: Composition, mechanisms, and antimicrobial functions

EOs are volatile, aromatic liquids extracted from various plant parts such as flowers, leaves, citrus peels, fruits, and herbs. These oils are typically obtained through steam or water distillation and are known for their pleasant aroma, insolubility in water, and broad applications, including food preservation. Common sources of EOs include garlic, cloves, chili, ginger, galangal, kaffir lime, and pomelo, which serve as raw materials for producing EOs with diverse biological and functional properties [8,9]. Beyond their role as flavor enhancers, EOs exhibit remarkable antimicrobial activity, which makes them effective in inhibiting or destroying microorganisms, particularly those responsible for spoilage and foodborne diseases. EOs are rich in bioactive compounds such as terpenes, terpenoids, and phenylpropanoids. Terpenes are composed of isoprene units (mono-, sesqui-, and diterpenes), while terpenoids include oxygenated derivatives such as alcohols, esters, aldehydes, ketones, ethers, and phenols. Notable terpenoids with antimicrobial properties include thymol, carvacrol, linalool, linalyl acetate, citronellal, piperitone, menthol, and geraniol. These compounds, present in sources like calamondin, pomelo, garlic, and cinnamon, contribute to the antimicrobial and antioxidant activity of EOs, particularly in seafood preservation [9-11]. The structural differences influence the antimicrobial action of EOs in the cell membranes of gram-positive and gram-negative bacteria. Gram-positive bacteria, such as Staphylococcus aureus, have hydrophobic cell membranes that are more susceptible to disruption by hydrophobic EOs components. For example, when combined with certain fatty acids, carvacrol increases cell membrane permeability and fluidity, leading to the leakage of compatible solutes and eventual microbial death [49].

Conversely, gram-negative bacteria, such as Escherichia coli, possess lipopolysaccharide-rich hydrophilic cell membranes, which provide more excellent resistance to hydrophobic compounds like phenolic antimicrobial agents (e.g., thymol, eugenol, and carvacrol) [2,3]. The antimicrobial mechanisms of EOs are complex and involve multiple pathways. These include disrupting cell wall integrity, altering cytoplasmic membrane properties, inhibiting ergosterol biosynthesis (a key component of cell membranes), altering lipid profiles, and inhibiting ATPase activity and biofilm formation. The effectiveness of EOs depends on factors such as concentration, the type of bioactive compounds present, and their functional groups [3,4]. Numerous studies have investigated the antimicrobial effects of EOs derived from citrus, herbs, and spices on seafood products. For example, calamondin (Citrus microcarpa Bunge), commonly used in Southeast Asia, contains phenolic acids such as p-coumaric and ferulic acid and flavonoid hesperidin [50]. The peel EOs of calamondin exhibit significant antimicrobial activity against spoilage microorganisms and pathogens, including Escherichia coli, Citrobacter freundii, Aeromonas hydrophila, Pseudomonas aeruginosa, Staphylococcus aureus, and Yersinia enterocolitica [50]. Similarly, pomelo (Citrus grandis L. Osbeck) peel EOs, rich in monoterpenes such as terpinyl acetate, α-pinene, β-pinene, and terpinolene, effectively inhibit spoilage microorganisms in saltwater fish fillets, targeting pathogens such as Yersinia pestis, Bacillus cereus, Escherichia coli, Staphylococcus aureus, Listeria monocytogenes, Pseudomonas aeruginosa, and Candida albicans.

These monoterpenes disrupt microbial membrane integrity and impair respiration [51]. EOs from herbs and spices also display significant antimicrobial activity. Garlic (Allium sativum), a well-known antimicrobial agent, contains organosulfur and phenolic compounds such as allicin, diallyl sulfide, diallyl trisulfide, diallyl disulfide, ajoene, and 2-vinyldithiins. Studies have shown that garlic EOs reduce total viable counts, coliform bacteria, and psychrophilic bacteria in seafood. For instance, rainbow trout treated with 1-2% garlic EOs showed a > 2 log CFU/g reduction in bacterial counts compared to untreated controls. This effect is attributed to the ability of garlic EOs to disrupt cell membranes, causing leakage of cellular solutes [52]. Cinnamon EOs have also been extensively studied for their antimicrobial effects. In comparative studies involving 9 EOs (including star anise, clove, basil, garlic, oregano, lemongrass, thyme, rosemary, and black pepper), cinnamon EOs demonstrated superior antimicrobial activity in Asian seabass fillets stored at 4 ± 1 °C. At a concentration of 488 mg/L, cinnamon EOs effectively inhibited Escherichia coli, S. Typhimurium, Staphylococcus aureus, and Vibrio parahaemolyticus, exhibiting the widest inhibition zones among the tested oils [53]. The antimicrobial efficacy of EOs highlights their potential for preserving seafood, leveraging their bioactive compounds to combat spoilage and pathogenic microorganisms while maintaining product quality and safety. Table 5 illustrates the EO’s source, bioactive compounds, and antimicrobial activities.

EFCs: Types, properties, and biopolymer matrices

EFCs have emerged as an innovative and sustainable alternative within the food packaging industry, offering environmental and functional advantages. This approach aligns with global efforts to address sustainability and food security challenges while optimizing food quality and reducing waste. Unlike traditional packaging, EFCs provide a biodegradable and safe solution to extend the shelf life of perishable goods, particularly in combating the global issue of food waste [8]. EFC materials are made from natural polymers, are safe for direct consumption, and are adaptable to various forms, such as films and coatings. Films are used in wraps, pouches, bags, capsules, and casings, serving as protective barriers around food items. Coatings, on the other hand, are directly applied to the surface of food, acting as integral components that maintain their protective and functional properties during consumption [9]. These films and coatings play a vital role in preserving and enhancing the quality of food products. They provide effective barriers against gases and moisture, regulate gas exchange, minimize ethylene production, and prevent moisture loss, maintaining the weight, flavor, and appearance of packaged foods. When infused with antioxidants and antimicrobial agents, EFCs also help inhibit spoilage, browning, and microbial activity. Furthermore, the versatility of these materials allows them to serve as nano-carriers, enabling the controlled release of additives for advanced preservation techniques [58]. The selection of EFC materials is tailored to the specific requirements of food products, ensuring compatibility with sensory characteristics to meet consumer expectations. This careful selection protects food from external factors and enhances its overall quality. Additionally, EFCs serve as a matrix for functional additives, including antimicrobial and antioxidant compounds, prebiotics, and other nutrients, improving packaged foods’ shelf life and nutritional value. By incorporating these compounds, EFCs enhance their structural, mechanical, and handling properties, broadening their applications [59]. Fish and seafood products are particularly suited for EFCs due to their high perishability. These products have high water activity values (0.95-0.98) and are rich in nutrients, making them highly susceptible to spoilage. Consequently, nearly 35% of global fish production is lost before consumption. To address this issue, developing ecologically sustainable packaging materials that can effectively preserve the freshness and quality of fish and seafood is imperative [9]. EFCs thus offer a promising solution, combining sustainability with enhanced preservation techniques to reduce waste, maintain product quality, and cater to growing consumer demands for environmentally friendly packaging alternatives.

Table 5 EO and their bioactive compounds and antimicrobial activities.