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. 2025 Apr 24;27:102496. doi: 10.1016/j.fochx.2025.102496

Edible coating of Farsi gum with Persian lime oil nanoemulsion and oxygen scavenger packaging to preserve chilled rainbow trout fillets

Hamidreza Heydari-Farsani a, Aziz A Fallah a,⁎, Abbas Mokhtari a, Mohammad Ghasemi b, Amin Mousavi Khaneghah c,d
PMCID: PMC12063025  PMID: 40351501

Abstract

In this study, the Farsi gum (FG) coating solution enriched with Persian lime essential oil nanoemulsion (LNE) was developed. The coating solution and oxygen scavenger (OS) packaging (FG + LNE + OS) were tested on the quality preservation of rainbow trout fillets during refrigerated storage. The findings indicate that incorporating LNE into the coating matrix and OS packaging significantly reduced the growth of total mesophilic and psychrotrophic bacteria, Enterobacteriaceae, and lactic acid bacteria. Additionally, these treatments effectively controlled the increase in pH, total volatile nitrogen, conjugated dienes, thiobarbituric acid reactive substances, protein carbonyls, electric conductivity, and sensory quality deterioration in the fillets. Among the various treatments, the combination of FG, LNE, and OS was most effective in preserving the quality of the fish. The shelf life assessment revealed that the control and FG-only groups had a shelf life of 4 days, while the OS and FG + OS groups extended this to 8 days. The FG + LNE treatment further increased the shelf life to 16 days, and the FG + LNE + OS combination achieved a minimum shelf life of 20 days. These results suggest that employing an active coating system with FG and LNE, alongside OS packaging, is a promising strategy for enhancing the preservation of chilled fish fillets, significantly extending perishable seafood's shelf life.

Keywords: Active packaging, Persian gum, Citrus latifolia, Oxygen absorber, Fish, Seafoods

Highlights

  • •

    Coating solution with Farsi gum (FG), lime oil nanoemulsion (LNE) was developed.

  • •

    LNE increased its in vitro antimicrobial and antioxidative activity.

  • •

    Trout fillets were coated with FG + LNE followed by oxygen scavenger (OS) packaging.

  • •

    Treatment with FG + LNE + OS conserved the quality parameters of trout fillets.

  • •

    The shelf life of chilled trout fillets was extended by FG + LNE + OS treatment.

1. Introduction

Fish products are recognized for their significant contributions to human health, underscoring their importance as a key element of a balanced diet. They are an excellent source of high-quality protein, essential amino acids, and vital vitamins and minerals. Nevertheless, the susceptibility of fish products to spoilage because of their inherent composition necessitates applying various preservation methods to minimize deterioration and extend their shelf life (Rabiepour et al., 2024; Saldanha Pinheiro et al., 2023; Suárez-Medina et al., 2024; Zu et al., 2023).

Active packaging represents an advanced and innovative strategy within food packaging designed to improve food products' quality, safety, and longevity. This approach integrates active substances or agents into packaging materials, enabling them to interact with the food environment and deliver additional functional benefits. Such agents may encompass antimicrobial compounds, antioxidants, oxygen scavengers, moisture regulators, and flavor or aroma enhancers. These components can modify the food matrix by actively releasing or absorbing specific substances, enhancing preservation and significantly extending shelf life (Fallah, Sarmast, Ghasemi, et al., 2023; Khan et al., 2024; Patil et al., 2023).

Adopting biopolymers for active food coatings presents a dual advantage, enhancing food preservation while providing a sustainable alternative to traditional synthetic coatings (Aziz et al., 2024; Dutta & Sit, 2024). Farsi gum (FG), also referred to as “Persian gum” or “Zedo gum,” is a natural biopolymer originating from the stem of mountain almond trees and is widely employed across various industries, including pharmaceuticals, food, and cosmetics, due to its versatile properties. This arabinogalactan-based hydrocolloid consists of water-soluble (∼30 %) and water-swellable (∼70 %) fractions. The soluble fraction can form a clear dispersion with favorable adhesive properties, making it highly suitable for coating applications (Joukar et al., 2017; Saffari Samani et al., 2023).

Essential oils (EOs) are natural substances widely acknowledged for their antimicrobial and antioxidative capabilities, positioning them as effective preservatives. Nevertheless, their utilization in food preservation is hindered by their volatile nature and the undesirable sensory attributes they impart at elevated concentrations. Embedding EOs within coating formulations enables a controlled and prolonged release, ensuring their persistent presence and optimal functionality in food preservation systems (Borah et al., 2024; Ferhat et al., 2025; Moghadas et al., 2024; Zhang et al., 2024). The EO derived from Citrus latifolia, known as Persian lime, comprises several active compounds, including polyphenols and terpenes, with remarkable antimicrobial and antioxidative properties (Sarmast et al., 2019).

In recent years, nanoemulsions have emerged as a transformative technology, experiencing a significant surge in adoption across various industries. These systems consist of water-in-oil or oil-in-water emulsions with droplet sizes in the nanoscale range (typically 20–200 nm). The increasing attention toward nanoemulsions is primarily attributed to their distinctive and beneficial characteristics, such as superior stability, resistance to gravitational separation, and the capacity to form optically transparent systems. The enhanced stability of these nanoemulsions not only extends the shelf life of food products but also improves the encapsulation and targeted delivery of bioactive compounds (Dini et al., 2020; Fallah, Sarmast, Jafari, & Mousavi Khaneghah, 2023; Moosavi-Nasab et al., 2023).

Oxygen scavengers (OS) are specifically designed to slow down the oxygen-dependent deterioration of food products through iron (Fe2+) oxidation, reducing oxygen levels within the packaging to <0.01 %. As one of the most widely recognized methods in active packaging, OS decelerates undesirable oxidative processes by eliminating oxygen and extending packaged products' shelf life (Elahi et al., 2024; Lee et al., 2024).

This study focused on developing a nanoemulsion formulated using Persian lime essential oil, which was incorporated into a Farsi gum-based solution. Subsequently, the combined effect of the coating solution and oxygen scavenger (OS) packaging on the quality parameters of trout fillets was evaluated during the chilled storage period.

2. Materials and methods

2.1. Materials

Farsi gum was purchased from Reyhan Gum Parsian Co. (Mazandaran, Iran). The pure Persian lime peel essential oil was obtained from Baridj Essence Co. (Kashan, Iran). The self-reacting OS sachets (BiHava®), which absorb 300 ml of oxygen, were provided by Baste Raz Salamat Paya Co. (Tehran, Iran) as a gift. Furthermore, Ageless-Eye® oxygen indicators were sourced from Mitsubishi Gas Chemical Co. in Tokyo, Japan. The study utilized high-barrier pouches composed of a multi-layer structure, specifically low-density polyethylene, ethylene vinyl alcohol, polyamide copolymer, and polyethylene terephthalate. These pouches exhibited a thickness of 112 μm and an oxygen transmission rate of 2.15 ml/m2 per 24 h at a temperature of 22 °C, and were procured from Plastic Alvan Company in Karaj, Iran. The culture media were obtained from Mirmedia Co. in Khorramshahr, Iran, for microbiological analyses. The research also employed analytical-grade chemicals to ensure the precision of the experimental procedures. The microbial strains utilized in this study included Staphylococcus aureus PTCC 1917, Listeria monocytogenes PTCC 1783, Escherichia coli O157:H7 PTCC 1860, and Salmonella typhimurium PTCC 1709, all of which were acquired from the Iranian Research Organization for Science and Technology, located in Tehran, Iran.

2.2. Gas chromatography–mass spectrometry (GC–MS) studies

Lime essential oil underwent a comprehensive compositional analysis using GC–MS, as the procedure established by Sarmast et al. (2019). The main components were d-limonene (59.8 %), β-pinene (16.6 %), and γ-terpinene (9.93 %).

2.3. Preparation and characterization of LNE

The preparation of the LNE was performed by blending LNE and Tween 80 in a volumetric ratio of 1:1 (v/v), followed by subjecting the mixture to ultrasonic homogenization (model UP400-A, TOP Sonics Co., Tehran, Iran), operating at a power of 450 W and a frequency of 20 kHz for 10 min. The concentration of EO in the emulsion was held at a fixed value of 6 % (v/v). Crushed ice was positioned around the emulsion beaker to mitigate the thermal effects of ultrasonication. The SZ-100 dynamic light scattering instrument (Horiba, Japan) was used to determine the LNE droplets' average particle size and the polydispersity index (PDI). Next, the prepared LNE formulation was stored in a sealed glass bottle at room temperature and monitored weekly for six weeks to assess the occurrence of phase separation or creaming.

2.4. Coating solution preparation

To prepare the coating solution, Farsi gum was placed in a beaker, distilled water was added, and then left at room temperature overnight to allow for water absorption. Afterward, the solution was heated on a hot plate at 60 °C and stirred until well homogenized. To dissolve the water-insoluble part of the gum, the solution was ultrasonicated for 10 min at a power of 450 W and a frequency of 20 kHz (Dehghani et al., 2018; Raoufi et al., 2019). After the solution reached ambient temperature, glycerol was added as a plasticizer (0.35 g/g of biopolymer) and mixed well. Finally, the LNE was slowly added to the coating solution and homogenized. The final concentrations of Farsi gum and LNE in the coating solution reached 2 % (w/v) and 1 % (v/v, based on the concentration of pure essential oil), respectively.

2.5. In vitro assessment of antimicrobial and antioxidative properties

The antimicrobial potential of three treatments—FG, FG + LNE, and streptomycin (used at a concentration of 100 mg/l as a positive control)—was examined against four notable foodborne pathogens: Listeria monocytogenes, Salmonella typhimurium, Escherichia coli, and Staphylococcus aureus. This evaluation was executed by agar disk diffusion technique (Jafarinia et al., 2022). In parallel, the antioxidant activity of FG, FG + LNE, and α-tocopherol (at 10 mg/ml, serving as a positive control) was assessed via their ability to scavenge 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radicals, employing the methodology detailed in our previous study (Hasani-Javanmardi et al., 2021).

2.6. Process of sampling

Rainbow trout weighing 450–500 g were obtained from an aquaculture facility ∼30 min after harvesting, and transported to the laboratory in an icebox to maintain low temperatures. Upon arrival, the fish underwent processing, which included beheading, evisceration, and filleting. The resulting fillets were then classified into six distinct groups, as detailed in Table 1. The fillets were then subjected to a 1.5-min immersion in appropriate solutions, after which they were drained and sealed in the pouches. These packages were stored at 3 ± 0.25 °C. Ageless-Eye oxygen indicators and OS sachets were integrated into the packages for the groups receiving OS treatments. Notably, the oxygen indicators transitioned from purple to pink within ∼7 h of refrigeration, signifying a reduction of oxygen levels to below 0.10 %. Once this change occurred, the pink coloration remained stable for the storage period, confirming the maintenance of a controlled environment. To monitor quality changes, fillet samples from each experimental group were analyzed at predetermined intervals: 0, 4, 8, 12, 16, and 20 days, with four individual samples examined at each time point.

Table 1.

Experimental design.

Group No. Treatment Description
1 Control Trout fillets soaked in double distilled water and then aerobically packed.
2 FG Trout fillets soaked in FG solution and then aerobically packed.
3 OS Trout fillets soaked in double distilled water and then packed with OS sachets.
4 FG + OS Trout fillets soaked in FG solution and then packed with OS sachets.
5 FG + LNE Trout fillets soaked in FG solution containing LNE and then aerobically packed.
6 FG + LNE + OS Trout fillets soaked in FG solution containing LNE and then packed with OS sachets.
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Abbreviations: FG, Farsi gum; OS, oxygen scavenger; LNE, lime essential oil nanoemulsion.

2.7. Microbiological analyses

To assess the microbial quality of the fish samples, an initial homogenization step was performed using a portion of fish flesh (10 g) mixed with 90 ml of a 0.9 % NaCl solution, and processed in a stomacher (Lab Blender 400, Seward Medical, UK) for 2.5 min. This homogenate was then serially diluted to ensure precision in subsequent microbial quantification. Quantification of total mesophilic bacteria (TMB) and total psychrotrophic bacteria (TPB) was carried out using the pour plate method on plate count agar; specifically, TMB was incubated at 30 °C for 72 h, while TPB was incubated at 7 °C for 7 days, to target the different growth characteristics of these microbial groups. For the selective enumeration of the Enterobacteriaceae family, a pour overlay method was employed on violet red bile dextrose agar, incubating at 35 °C for 24 h. In addition, lactic acid bacteria (LAB) were quantified employing the pour plate method on de Man–Rogosa–Sharpe agar, with an incubation period of 72 h at 30 °C. The results of all microbial assays were ultimately expressed as the logarithm of colony-forming units per gram of tissue (log CFU/g) (Fallah et al., 2008; Shahabi et al., 2024).

2.8. Physicochemical studies

Herein, standardized procedures from prior research were utilized to evaluate key quality parameters of the samples. Specifically, the analyses included measurements of pH, total volatile basic‑nitrogen (TVB-N), conjugated dienes (CDs), thiobarbituric acid reactive substances (TBARS), protein carbonyls (PCs), and electrical conductivity (EC) (Dini et al., 2020; Fallah et al., 2010).

2.9. Sensory analysis

Thirty semi-trained sensory assessors were engaged to conduct a comprehensive evaluation of trout fillets. Each participant signed an informed consent form after receiving a complete explanation of the study protocol. This study systematically investigated the sensory profile by considering critical parameters such as texture, appearance, odor, and overall acceptability. The fish fillets were labeled with random 3-digit numbers and presented to the panelists on white plates with cover lids. No information regarding the treatments was provided to the panelists during sample assessment. The evaluation was conducted using a 9-point hedonic scale, where a score of 1 represented “extremely dislike” and a score of 9 corresponded to “extremely like.” Scores ranging from 5 to 9 were interpreted as indicative of varying degrees of acceptability (Sarmast et al., 2019).

2.10. Statistical studies

The study employed a two-way ANOVA using SPSS Version 22 to evaluate the influence of treatment modalities and storage durations on the assessed parameters. Then, Duncan's multiple range test was applied to perform detailed pairwise comparisons among group means, with a significance criterion at P ≤ 0.050.

3. Results and discussion

3.1. The nanoemulsion characteristics

The LNE exhibited an average particle size of 79.8 nm (32.6–161.6 nm) and a PDI of 0.465. The LNE demonstrated stability throughout a 6-week storage period at room temperature, with no observable phase separation or creaming.

3.2. Investigation of antimicrobial and antioxidative properties

The experimental findings displayed in Table 2 underscore the comparative efficacy of coating solutions FG and FG + LNE in mitigating the proliferation of foodborne pathogens under in vitro conditions. While the sole application of FG demonstrated limited inhibitory effects on pathogen growth, the supplementation of LNE within the coating matrix (FG + LNE) yielded a profound enhancement in antimicrobial activity. Notably, the active coating matrix exhibited a higher effectiveness against Gram-positive bacterial strains, specifically L. monocytogenes and Staph. aureus, when contrasted with Gram-negative strains like S. typhimurium and E. coli O157:H7. The capability of Gram-negative bacteria to endure antimicrobials is related to the unique structure of their cell wall, which functions as a barrier impeding the passage of antimicrobial substances through their outer membranes (Jafarinia et al., 2022). Also, the antimicrobial efficacy demonstrated by the active coating matrix can be related to the phenolic compounds of the LNE (Tran et al., 2021).

Table 2.

In vitro antimicrobial activity (zone of inhibition, mm) and DPPH radical scavenging activity (% inhibition) of coating solutions.

Microorganism Formulations
FG FG + LNE Streptomycin α-Tocopherol
Antimicrobial activity
Escherichia coli O157:H7 0.00a,b,c, w,x,y,z 10.3 ± 0.61a,b,c, w,x,y,z 15.9 ± 0.19a,b,c, w,x,y,z –
Salmonella typhimurium 0.00a,b,c, w,x,y,z 11.4 ± 0.59a,b,c, w,x,y,z 19.8 ± 0.23a,b,c, w,x,y,z –
Staphylococcus aureus 0.00a,b,c, w,x,y,z 14.6 ± 0.52a,b,c, w,x,y,z 24.2 ± 0.23a,b,c, w,x,y,z –
Listeria monocytogenes 0.00a,b,c, w,x,y,z 15.5 ± 0.64a,b,c, w,x,y,z 21.5 ± 0.31a,b,c, w,x,y,z –
Antioxidative activity
DPPH radical scavenging 3.15 ± 0.08a 59.8 ± 2.36b – 90.9 ± 3.01c
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Data are mean ± SD (n = 4).

Abbreviations: FG, Farsi gum; LNE, lime essential oil nanoemulsion; DPPH, 1,1-diphenyl-2-picrylhydrazyl.

a,b,c

Means ± SD within a same row with different superscript letters are significantly different (P ≤ 0.050).

w,x,y,z

Means ± SD within a same column with different superscript letters are significantly different (P ≤ 0.050).

Table 2 presents an analysis of the in vitro antioxidant characteristics of the coating solutions, specifically in terms of their capacity to neutralize DPPH free radicals. The FG coating solution exhibited minimal antioxidant effectiveness (< 3.20 %), whereas integrating LNE into the coating matrix considerably elevated its antioxidative capacity. It is suggested that the primary antioxidative properties of LNE are attributed to its phenolic components, which serve as free radical scavengers (Toscano-Garibay et al., 2017).

3.3. Microbial flora analyses

According to Fig. 1, primary counts for TMB, TPB, and Enterobacteriaceae in the trout fillets ranged from 4.08 to 4.63, 3.28 to 3.53, and 2.31 to 2.95 log CFU/g of flesh, respectively. The measured values demonstrated no statistically significant differences among the groups, suggesting that the fillets possessed an acceptable microbiological quality level at the study's beginning. Throughout the storage period, all experimental groups consistently noted a steady increase in the counts of total mesophilic bacteria (TMB), total psychrotrophic bacteria (TPB), and Enterobacteriaceae. Specifically, the control and FG groups displayed a markedly higher bacterial growth rate than the remaining groups. Our result for TMB enumeration demonstrated that the control and FG groups exceeded the permissible microbial limit of 7 log CFU/g of flesh on day 8. In contrast, the OS and FG + OS groups surpassed this threshold on day 12. On the other hand, the FG + LNE group showed a slower rate of microbial proliferation and exceeded the established limit at day 20 of storage. In contrast, the FG + LNE + OS group consistently maintained a microbial load below the permissible threshold across the entire storage period. By the conclusion of the storage period (day 20), a comparative analysis of TMB, TPB, and Enterobacteriaceae counts revealed no statistically significant differences between the control and FG, nor between the OS and FG + OS groups. However, the OS and FG + OS treatments demonstrated a more pronounced ability to suppress microbial growth in refrigerated fillets relative to the FG treatment. In comparison, the FG + LNE treatment exhibited a significantly enhanced capacity to retard microbial proliferation when contrasted with both the OS and FG + OS treatments. Most notably, the FG + LNE + OS treatment proved to be the most effective in inhibiting microbial growth, surpassing all other therapies in efficacy. GhareAghaji et al. (2021) reported that the application of an active biopolymer coating impregnated with a citrus essential oil nanoemulsion retarded the growth of TMB, TPB, and coliforms in chill-stored trout fillets. In another research, wrapping turkey burgers in a biopolymer film containing cumin essential oil nanoemulsion, followed by OS packaging, was an efficient technology to decrease the TMB, TPB, and coliform counts at chilled conditions (Shahabi et al., 2024).

Fig. 1.

Fig. 1

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Microbial flora counts of rainbow trout fillets treated with Farsi gum (FG), Persian lime essential oil annoemulsion (LNE), and oxygen scavenger (OS) packaging during chilled storage. Data are mean ± SD (n = 4).

The initial levels of LAB in fillets across various groups were recorded in the range of 2.19–2.41 log CFU/g of flesh. Throughout the storage period, LAB counts demonstrated a general trend of increase in all groups. Notably, the control, FG, OS, and FG + OS groups exhibited markedly higher growth rates than the others. As a result, no statistically significant differences were detected among the latter groups by day 20 (Fig. 1). Prior research findings have identified the growth potential of LAB in various muscle-based food items under both aerobic conditions and in the OS packaging (Chounou et al., 2013; Karimzadeh et al., 2024; Mohan et al., 2019; Shahabi et al., 2024). Our current study aligns with such reports, as we have also observed similar outcomes. According to the results obtained from our research, it was found that the inclusion of LNE in the coating formulation (FG + LNE and FG + LNE + OS) demonstrated superior effectiveness in inhibiting the growth of LAB in refrigerated fillets, surpassing the effectiveness of the other treatment groups (Fig. 1).

Research on the antimicrobial efficacy of lime essential oil has established that its robust antimicrobial attributes predominantly originate from the existence of monoterpenic elements like limonene, β-pinene, and γ-terpinene (Tran et al., 2021; Van et al., 2024), which serve as the main components within the lime essential oil applied in the current study. The lipophilic characteristics of the essential oil, in conjunction with its particular monoterpenic constituents, promote its penetration into the cytoplasmic membrane of microbial cells, leading to cell demise (Elahi et al., 2024). The small dimensions of nanoscale particles coupled with the enhanced aqueous dispersibility inherent in nanoemulsion-derived compounds speed up their transmission across the bacterial cell membrane, thereby amplifying their antimicrobial efficacy compared to their conventional counterparts (Shahabi et al., 2024). Researchers have revealed that the utilization of OS sachets in the packaging of food products effectively diminishes oxygen levels to below 0.01 %, thereby controlling the proliferation of aerobic microorganisms (Hasani-Javanmardi et al., 2021). Our results show that integrating an active coating with OS packaging enhances the effectiveness of inhibiting microbial proliferation in fish fillets, likely due to the additive or synergistic effects of the abovementioned combined strategies.

3.4. Physicochemical studies

Outcomes of the physicochemical assessments conducted on trout fillets are illustrated in Fig. 2. The initial pH values ranged between 6.50 and 6.60 in the fillets across various groups. By the fourth day of the experiment, a minor decline in the pH of fillets was noted across all groups, a typical phenomenon attributed to the formation of lactic acid due to the degradation of ATP-linked compounds (Sarmast et al., 2019). In the later stages of the experiment, all groups exhibited a significant rise in pH levels, which can be initially related to the metabolic activities of microbiota and the resulting production of volatile basic compounds, reflecting changes in the biochemical environment of the trout fillets (Azizi et al., 2024). The rates of pH increase in the control and FG groups surpassed those of the remaining groups over the storage time. In contrast, the interventions incorporating OS and LNE effectively mitigated the rise in pH in trout fillets, a phenomenon likely originating from suppressing microbial flora activity. On the last day of the storage period, no substantial difference was observed in pH levels between the control and FG groups, nor between the OS and FG + OS groups. The efficacy of the OS and FG + OS treatments surpassed that of FG alone. In contrast, the FG + LNE treatment exhibited greater effectiveness than both the OS and FG + OS treatments in retarding the pH elevation rate in refrigerated fillets. The combination of FG + LNE + OS is the most effective treatment.

Fig. 2.

Fig. 2

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Physicochemical parameters of rainbow trout fillets treated with Farsi gum (FG), Persian lime essential oil nanoemulsion (LNE), and oxygen scavenger (OS) packaging during chilled storage. Data are mean ± SD (n = 4).

The TVB-N index is an important chemical indicator for evaluating the freshness of a range of muscle-based products (Bekhit et al., 2021). At the beginning of the study, the TVB-N levels in trout fillets from the various groups were between 11.9 and 14.2 mg N/100 g of flesh, indicating that the fillets were of acceptable quality. The acceptable TVN levels were 25–30 mg N/100 g and 24 mg N/100 g based on the European Commission (2008) and the Iran Veterinary Organization (2009) regulations. As the storage period advanced, a steady increase in TVB-N was found in all groups, with the control and FG groups demonstrating a more significant rise relative to the others. As shown, the TVB-N levels surpassed the threshold of 24 mg N/100 g of flesh, as outlined by the Iran Veterinary Organization (2009), on the 8th day for the control and FG groups, on the 12th day for the OS and FG + OS groups, and the 20th day for the FG + LNE group. Notably, the FG + LNE + OS group maintained TVB-N levels below this regulatory limit throughout storage time. By the conclusion of the storage period, no statistically significant differences were found in the TVB-N levels between the control and FG, nor between the OS and FG + OS groups. Nonetheless, we realized that the groups involving OS and FG + OS were more effective in curbing the increase in TVB-N levels than FG's sole application. Moreover, the FG + LNE treatment exhibited superior efficacy in retarding the rise of TVB-N levels in comparison to the OS and FG + OS treatments. Significantly, the combination of FG + LNE + OS was recognized as the best approach in this context (Fig. 2). It is widely acknowledged that TVB-N is associated with the degradation of protein and non-protein nitrogenous substances, a process driven by bacterial proteolytic enzymes leading to the production of volatile nitrogenous compounds (Pirastehfard et al., 2021; Zomorodian et al., 2023). The lower TVB-N levels observed in groups treated with OS and LNE might be ascribed to the effective suppression of microbial growth, limiting their ability to break down nitrogenous components within the fish flesh. In this vein, Sarkar et al. (2024) demonstrated that chitosan coating followed by OS packaging effectively mitigated the level of TVB-N accumulation in Hilsa fish over 28 days of chilled storage. Furthermore, another investigation showed that the combined utilization of active coating and OS packaging effectively limited the rate of TVB-N increase in refrigerated trout fillets (Karimzadeh et al., 2024).

The CDs are primary oxidation products that result from the degradation of polyunsaturated fatty acids found in fish tissues. These compounds are significant as they indicate the initial stages of lipid oxidation. In contrast, the TBARS index evaluates secondary lipid oxidation by-products, particularly those forming aldehydes, which suggest further oxidative deterioration. Conversely, PCs are formed due to amino acid side chain oxidation, serving as a standard metric for evaluating protein oxidation (Günal-Köroğlu et al., 2025; Wu et al., 2022). Initially, the levels of CDs, TBARS, and PCs in the trout fillets across various groups ranged from 0.13 to 0.18 mmol of CDs/g of flesh, 0.50 to 0.78 mg MDA/kg of flesh, and 0.84 to 1.07 nmol of carbonyls/mg of protein, respectively. Over the storage duration, a continuous elevation in the levels of the indicators above was detected across all experimental groups. However, the control and FG demonstrated a markedly greater increase in these concentrations than the other groups. On the 20th day, there were no significant statistical differences in levels of CDs, TBARS, and PCs when comparing the control group with the FG group, nor when comparing the OS group with the FG + OS treatment. Nevertheless, we found that treatments involving OS and FG + OS demonstrated better efficacy in decelerating the lipid and protein oxidation level in refrigerated fillets than with FG alone. Furthermore, the FG + LNE treatment exhibited superior efficiency in retarding the progression of lipids and protein oxidation in comparison to the OS and FG + OS interventions. Notably, the FG + LNE + OS combination proved the most efficacious approach (Fig. 2). A strong interdependence is observed among the oxidative pathways influencing lipids and proteins in muscle-based food products. Such a relationship may be explained by the transfer of oxidation reactions from secondary lipid oxidation products to protein structures (Günal-Köroğlu et al., 2025; Ivane et al., 2024). Studies investigating the antioxidative properties of Persian lime essential oil have established that its robust antioxidative capabilities stem from the presence of monoterpenic compounds such as limonene, β-pinene, and γ-terpinene (Pateiro et al., 2018), which serve as the major chemical constituents in the essential oil used in this study. Notably, incorporating OS sachets in packaged food products has diminished oxygen levels to <0.01 %, thereby hindering oxidative reactions (Lee et al., 2024). Our results suggest that the combined use of active coatings alongside OS packaging enhances the ability to mitigate oxidative reactions in trout fillets, potentially due to additive or synergistic effects arising from the simultaneous application of these treatments.

The EC, a parameter closely associated with electrolyte concentration, is a unique metric for assessing fish quality (Karimzadeh et al., 2024). The initial EC values in trout fillets varied between 1.01 and 1.14 ms/cm across experimental groups, with statistically significant differences among groups not emerging until the fourth day of storage. Throughout the storage period, EC levels increased consistently among all groups, with the control and FG groups exhibiting a substantially more significant elevation than the other treatments (Fig. 2). The increase in EC values likely mirrors the ongoing structural breakdown of fish tissue during storage. As the cellular structure deteriorates, electrolytes are released into the surrounding environment, a phenomenon driven by microbial activity and oxidative processes (Sarmast et al., 2019). Given that interventions incorporating OS and LNE effectively suppress microbial activity and retard oxidative processes, the EC values in the trout fillets subjected to these treatments were significantly lower. Notably, the FG + LNE + OS treatment proved to be the most effective intervention in mitigating these effects.

3.5. Sensory analyses

Fig. 3 illustrates the sensory evaluation outcomes for trout fillets across various experimental groups. Initially, attributes such as texture, odor, appearance, and overall acceptability received high ratings, consistently exceeding 8.45, which indicates a strong baseline quality across all groups. The ratings assigned to the sensory attributes remained satisfactory (scoring ≥ 5) until day 8 for the control and FG-treated fillets, day 12 for OS and FG + OS treatments, and day 20 for the FG + LNE and FG + LNE + OS groups. Despite exceeding acceptable limits for TMB and TVB-N levels across all experimental groups, organoleptic characteristics of the fillets consistently fell within acceptable thresholds. Our findings align with prior studies that have applied active coatings in preserving muscle-derived food products (Fallah et al., 2022; Jafarinia et al., 2022; Karimzadeh et al., 2024). This phenomenon arises somewhat from the active coating's ability to mask sensory deficiencies in muscle-based foods.

Fig. 3.

Fig. 3

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Sensory attributes of rainbow trout fillets treated with Farsi gum (FG), Persian lime essential oil nanoemulsion (LNE), and oxygen scavenger (OS) packaging during chilled storage.

The shelf life of trout fillets was determined by assessing a combination of indices, such as TMB counts, TVB-N levels, and comprehensive overall acceptability ratings. Based on these evaluative metrics, it was established that fillets in the control and FG groups maintained acceptable quality for only 4 days. In contrast, those treated with OS or FG + OS extended this period to 8 days, while the FG + LNE treatment further prolonged shelf life to 16 days. Notably, the FG + LNE + OS treatment offered the most significant improvement by extending the shelf life to a minimum of 20 days.

4. Conclusions

It is concluded that the incorporation of LNE into the coating formulation applied to trout fillets, as well as the use of OS packaging, demonstrated a marked capacity to inhibit microbial proliferation and retard adverse physicochemical changes in the fillets. Importantly, the treatment combining FG, LNE, and OS was determined to be the most effective in achieving these outcomes. These findings suggest that employing an active FG-based coating enriched with LNE in conjunction with OS packaging may be a promising strategy for preserving the quality and extending the shelf life of refrigerated fish fillets.

Ethical Statement

Appropriate protocols for protecting the rights and privacy of all sensory panel participants were utilized during the study. The participants were informed that their data/responses would remain confidential, and the results of the sensory tests were presented exclusively in aggregate form. They knew there was no requirement to eat the fish samples and understood they could withdraw from the project without providing a reason. The Educational and Research Council of the Faculty of Veterinary Medicine at Shahrekord University approved the sensory analysis protocol.

CRediT authorship contribution statement

Hamidreza Heydari-Farsani: Writing – original draft, Investigation, Conceptualization, Formal analysis. Aziz A. Fallah: Writing – review & editing, Supervision, Software, Investigation, Formal analysis, Data curation. Abbas Mokhtari: Writing – review & editing, Project administration, Conceptualization. Mohammad Ghasemi: Writing – review & editing, Investigation. Amin Mousavi Khaneghah: Writing – review & editing, Conceptualization, Formal analysis.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This study is part of H. Heydari-Farsani's Master's thesis, conducted under the supervision of Prof. Dr. Aziz A. Fallah and the advisement of Dr. Abbas Mokhtari. The thesis protocol received approval and financial support from the Faculty of Veterinary Medicine at Shahrekord University.

Data availability

Data will be made available on request.

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Data Availability Statement

Data will be made available on request.

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