
==== Front
Food Chem X
Food Chem X
Food Chemistry: X
2590-1575
Elsevier

S2590-1575(24)00637-0
10.1016/j.fochx.2024.101749
101749
Research Article
Enhancement of the quality and preservation of frozen burgers by active coating containing Rosa canina L. extract nanoemulsions
Ashrafi Azam a
Ahari Hamed dr.h.ahari@gmail.com
a⁎
Asadi Gholamhassan a
Mohammadi Nafchi Abdorreza bcd
a Department of Food Science and Technology, Science and Research Branch, Islamic Azad University, Tehran, Iran
b Department of Food Science and Technology, Damghan Branch, Islamic Azad University, Damghan, Iran
c Food Technology Division, School of Industrial Technology, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia
d Strategic Research Institute, Asia Pacific University of Technology and Innovation (APU), Jalan Teknologi 5, Kuala Lumpur 57000, Malaysia
⁎ Corresponding author at: Hamed Ahari, Department of Food Science and Technology, Science and Research Branch, Islamic Azad University, Tehran, Iran. dr.h.ahari@gmail.com
17 8 2024
30 10 2024
17 8 2024
23 10174922 5 2024
5 8 2024
16 8 2024
© 2024 The Authors
2024
https://creativecommons.org/licenses/by-nc/4.0/ This is an open access article under the CC BY-NC license (http://creativecommons.org/licenses/by-nc/4.0/).
This study aimed to assess the impact of an edible coating holding within chia seed gum (CSG) and Rosa canina L. extract (RCE) nanoemulsions (10%, 20%, and 40% w/w) on the oxidation, microbial load, and sensory characteristics of burgers in a 90-day frozen storage period. Based on the findings, the active CSG coatings showed remarkable antioxidant and antimicrobial activities. By increasing the level of RCE nanoemulsions, the functional activity of coatings significantly increased (P < 0.05). Upon the termination of the storage period, the lowest microbial load (i.e., a decrease of 0.5–2 log CFU/g in the number of different bacteria compared to the control) and oxidation stability were observed in burgers coated with a CSG solution containing 40% RCE nanoemulsions. This burger also showed the highest sensory acceptance on the last day. In conclusion, it is proposed to use the active coating produced in this study to maintain meat products' quality and safety and increase their shelf-life.

Highlights

• The Rosa canina L. extract (RCE) used as a novel additive for extending burgers' shelf life.

• RCE40%/chia seeds gum (CSG) reduced microbial growth by 30% of total viable count.

• RCE40%/CSG improved peroxide (48%) stability resulting longer burgers' shelf life.

• Active coating retained the color and sensory acceptance of frozen burgers for 90 days.

Keywords

Plant extract nanoemulsions
Antioxidant activity
Oxidation stability
Frozen burger preservation
Microbial load reduction
Shelf-life extension
==== Body
pmc1 Introduction

Meat is a crucial part of the human diet due to its high moisture content and nutrient content. However, concerns about microbial growth, especially in refrigerated meat, and the use of artificial preservatives raise concerns about carcinogenic effects. The debate is ongoing on replacing synthetic preservatives with natural antimicrobial agents (Gorzin et al., 2024).

The utilization of edible coatings and films is one of the most effective and important techniques to increasing the shelf-life of food products and preserve their quality and safety during the storage period (Ashrafi et al., 2023). These active systems, which are biodegradable and have an environmentally friendly relationship, can carry and deliver various bioactive compounds containing antioxidant and antimicrobial properties. Therefore, they can prevent the oxidation of lipids and microbial spoilage and inhibit unwanted changes in the color of food products (Ashrafi et al., 2018; Zhang et al., 2023). Since active agents incorporated in food coatings are gradually released from the coating or film into the food, it is preferable to add the active agents directly to food products for longer functional and maintenance activities (Esmaeili et al., 2024).

Previous studies have used various edible coatings and films based on polysaccharides and proteins, such as corn starch (Amiri et al., 2019), pectin, and various gums (Ansarian et al., 2022; Esmaeili et al., 2020), to increase meat and meat products' shelf-life. Salvia hispanica L. or chia seeds are rich sources of carbohydrates (∼42%), lipids (∼25–40%), proteins (∼17–24%), and essential fatty acids (∼60–80% of lipids). These seeds contain water-soluble and anionic mucilage, which is separated from the coat of the seeds (Esmaeili et al., 2024). Chia seed gum (CSG) has various functional activities in the food industry, including gelling, emulsifying, thickening, and bulking. Furthermore, CSG is considered a rich source of dietary fiber, a fat substitute, and a coating or film agent (Eslamian Amiri et al., 2021).

Rosa canina L., or dog-rose, is reported as a shrub species possessed by the Rosaceae family and dispensed throughout Europe, Asia, and North Africa. Rosa canina L. is rich in several bioactive compounds, including phenolic acids 48.8 mg / kg (i.e., gallic acid, ellagic acid, resveratrol, apigenin, and kaempferol), flavonoids 78–102 mg of the equivalent of gallic acid/ g fruit (i.e., anthocyanins, catechin, procyanidins, and quercetin), carotenoids (i.e., zeaxanthin, β-carotene, and lycopene), 1007.63–1901.47 mg% ascorbic acid, Anthocyanins 231–315 mg%, tocopherols, and minerals (i.e., calcium, phosphorous, and potassium). Therefore, Rosa canina L. has different biological and functional activities, such as antimicrobial, anti-carcinogenic, anti-inflammatory, and antioxidant properties (Rovná et al., 2020). Soltan et al. (2023) investigated the potential of Rose fruit extract (RCFE) as a natural antioxidant to increase the shelf life of mayonnaise. Mayonnaise samples containing different concentrations of RCFE (0.125 to 0.75%) were compared with a control sample (C1) and a sample containing 0.02% BHT (C2) >60 days of storage at 4 °C. It was found that RCFE can effectively reduce lipid oxidation and maintain sensory quality in mayonnaise, thus acting as a natural preservative substitute. Also, the effect of edible coating containing CSG and RCE nanoemulsion on the quality of beef-turkey hamburgers showed that oil absorption, acrylamide and 5-hydroxymethyl-2-furfural (HMF) content, and sensory characteristics of burgers had a positive and significant effect. It increased the antioxidant activity while maintaining the performance of the coating (Ashrafi et al., 2024).

Despite the preservative and health effects of plant extracts and essential oils, these active agents often have a characteristic odor, taste, and color, and their incorporation into food formulations might have adverse effects on the organoleptic properties of food products. Additionally, the stability of these compounds is often low against polymerization and oxidation; the encapsulation process is used to overcome this problem (Esmaeili et al., 2020). In this process, the active agent is coated with different wall materials, including lipids, carbohydrates, or proteins, and nanoemulsions act as delivery systems based on lipids (Gorzin et al., 2024; Guo et al., 2024). A massive quantity of energy is needed to fabricate nanoemulsions due to their non-equilibrium systems. Several methods have been applied for the preparation of nanoemulsions such as high-energy methods (like high-pressure homogenization, high ultrasound frequency, and microfluidization), and low-energy methods (such as phase inversion temperature, spontaneous emulsification, hydrogel method) (Xu et al., 2024). Among them, the ultrasonic technique has the advantages of reduction of the droplet sizes and uniform distribution (Ashrafi et al., 2024).

This investigation aimed to assess the antioxidant and antimicrobial activities of an edible coating containing Rosa canina L. extract (RCE) nanoemulsions on turkey burgers' quality in 90 days stored at a freezing point.

2 Materials and methods

2.1 Materials

Day-slaughtered beef and turkey were purchased from the local market (Iran) and transferred to the laboratory in ice-containing bags. Chia seeds and burger spices included Hindi nutmeg, black pepper, and cumin seed powder, which were purchased from the local market (Iran). Blue cheese was also provided by Kaleh Co. (Iran). Rose hip without seeds of Rosa canina L. was collected from the mountains around Bojnord, Iran. All chemicals, culture media, and reagents were of an analytical grade and obtained from Merck Co. (Germany). To prepare the carrot pulp, briefly, Nantes carrot cultivars were washed in water, and after cutting them into pieces with an average thickness of 5.5 mm, they were steamed at 105 °C for 10 min. The blanched carrots were then mixed in distilled water, and water was extracted. The carrot pulp was also placed in ethylene bags and stored in a refrigerator.

2.2 Extraction of CSG and determination of its chemical composition

The chia seeds were mixed in water (ratio, 1:20 w/v) at a temperature of 50 °C for 30 min. Subsequently, the produced suspension was milled using a mixer and boiled once more in a stirrer at 50 °C for 15 min. Afterward, the crude mixture was centrifuged (Finetech, Korea) for 3 h at 9460g at 15 °C. The obtained CSG was dried overnight at 40 °C and then ground to a powder for 40 s using a Kinfete 1095 grinder (Foss Analytical AB, Sweden) (Segura-Campos et al., 2014). The chemical composition of CSG, including its moisture (44–15.02), ash (08–01.01), protein (46–13.01), and fat (30–25.01) contents, was examined according to the standard American Association for Clinical Chemistry (AACC) methods (AACC, 2010).

2.3 Preparation of RCE and measurement of its total phenol content (TPC) and antioxidant activity

Rosa canina L. was collected from the mountains around Bojnord, Iran. After being approved by the herbarium department (Iran), it was dried under shade and ground to prepare the extract. First, water and ethanol (CAS 64–17-5, Merck, Germany) were blended at a ratio of 30:70 v/v. Then, 500 mL of the solvent was added to 200 g of plant powder; then, the blend was stirred on a shaker VORTEX 3 - IKA (IKA, Germany) overnight at room temperature. Subsequently, the blend was filtered using a No. 4 Whatman filter paper in a rotary evaporator QR 2005-S (Shimatzo, Japan), and the extract was concentrated at 40 °C. The resulting RCE was kept in a refrigerator until further use. The total phenol content (TPC) of RCE was calculated using the Folin-Ciocalteu assay based on a study by Gorzin et al. (2024). Moreover, the RCE's antioxidant activity was calculated by the DPPH radical scavenging method at 517 nm using a Uv-visible spectrophotometer (Hitachi, Japan) and expressed as the half-maximal inhibitory concentration (IC50) (Azarashkan et al., 2022).

2.4 Preparation of RCE-loaded nanoemulsions

The RCE nanoemulsions were prepared using the ultrasonication method, based on a method proposed by Harimurti et al. (2021) with some modifications. The water-in-oil emulsion (W/O) prepared in this study consisted of a 30% v/v aqueous phase and a 70% v/v oil phase (sunflower oil). The oil phase consisted of a 5% w/w polyglycerol polyricinoleate (PGPR) emulsifier. The RCE (15% w/w) was added in drops to the oil and surfactant blend while stirring at a rotational speed of 500 rpm at 40 °C by a magnetic stirrer (Heidolph, Hei-PLATE Mix 20, Germany). The prepared mixture was then stirred at 700 rpm for 20 min and transferred to an ultrasonic homogenizer (JY32-11 N Ultrasonic homogenizer; Ningbo Scientz Biotechnology Co. Ltd) for further homogenization (frequency 20 kHz for 4 min).

2.4.1 Investigation of particle size and zeta potential of RCE nanoemulsions

The particle size of RCE-loaded nanoemulsions was evaluated using dynamic light scattering (Malvern Zetasizer, UK) at an angle of 90° at a temperature of 25 °C (Chen et al., 2024). Before the test, the nanoemulsion was diluted in phosphate-buffered saline (pH = 7.4) at a ratio of 1:50 and then scattered at 657 nm. The zeta potential of the sample was also determined using a zeta potential analyzer at 25 °C (Azarashkan et al., 2022).

2.5 Preparation of edible CSG-based coating solution

For the preparation of the coating solution, 4 g of CSG powder (A preliminary test was conducted to choose the suitable level of CSG and it was observed that 4% is optimal for coating burgers based on the appearance characteristics (absence of cracks) of coated burgers that were stored in a freezer at −18 °C for one week (data not shown)), was mixed in Tween 80 (1 mL) and diluted to a final volume of 100 mL using distilled water. Subsequently, the mixture was agitated with a magnetic stirrer (Hei-PLATE Mix 20, Germany) (Heydari et al., 2020). Then, RCE-loaded nanoemulsions were added to the gum solution at concentrations of 10%, 20%, and 40% (The levels of RCE% was selected based on the preliminary test of the minimum inhibitory concentrations of Staphylococcus aureus).

2.5.1 Study the morphology and chemical interactions of edible coatings

The morphology of CSG-based edible coatings was studied using field emission scanning electron microscopy (FE-SEM; ZEISS, Germany). The chemical interactions between CSG and RCE-loaded nanoemulsions were investigated using Fourier transform-infrared (FT-IR) spectroscopy (THERMO NICOLET, USA) in the 4000–400 cm−1 wavenumber range (Li et al., 2024).

2.6 Burger preparation and coating application

The technique put forward by Ashrafi et al. (2024) was adopted in this study with some modifications to produce the burger samples. First, beef and turkey meat were ground separately in a meat grinder above 0° (Panther V2 M12.001, BEEM, Germany) with a 3–5 mm hole diameter to obtain a homogeneous mixture. For the preparation of the burger samples (weight: 100 g), 1.2% salt, 0.1% black pepper, 0.1% Hindi nutmeg, 0.05% cumin seed powder, and 18.5% chopped onion were added to 50% minced meat (i.e., a mixture of beef and turkey at equal proportions) and mixed. Next, carrot pulp (10%) and blue cheese (20%) were added and mixed completely by hand for three min and then homogenized in a commercial mixer (Kika-Labortechnika, Germany) for 8 min to prepare the burgers. The produced meat mixture was then placed in a hand mold and formed into burgers with an average diameter of 10 cm and a thickness of 10 mm.

To coat the samples with different the coating solutions (Table 1), the burgers were immersed in coating solutions for 2 min and then placed on a mesh tray for 3 min to remove excess solution (Fig. 1). Finally, the coated burgers were packed in polyethylene bags and kept at a freezer temperature (−18 °C) for 90 days. The experiments were performed on the burger samples (uncoated burgers (C), burgers coated with chia seed gum without RCE nanoemulsions (CSG), and burgers coated with different concentrations of RCE nanoemulsions) once every 30 days.Table 1 Burger samples studied in this research.

Table 1Treatments	Description	
C	Control sample (Burgers without coating)	
CSG	Coated burgers with 4% (w/w) CSG solution	
CSG-10RCE	Coated burgers with 4% CSG solution containing 10% RCE-nanoemulsion	
CSG-20RCE	Coated burgers with 4% CSG solution containing 20% RCE-nanoemulsion	
CSG-40RCE	Coated burgers with 4% CSG solution containing 40% RCE-nanoemulsion	

Fig. 1 Coating of beef-turkey burgers with active CSG solutions: A) Appearance of CSG solutions, B) Burger samples, and C) Coated burgers.

Fig. 1

2.7 Experiments on burgers

2.7.1 Measurement of pH

A digital pH meter (Metrohm, Switzerland) was employed to measure the pH of the burger samples. Before performing the test, the pH meter was calibrated with different buffer solutions. Subsequently, the samples (10 g) were mixed with distilled water (100 mL); the sample's pH was recorded by allowing the solution at room temperature for 5 min (Emiroğlu et al., 2010).

2.7.2 Measurement of lipid oxidation

The peroxide value (PV) of the samples was determined using the standard method of the American Oil Chemists' Society (AOCS) method. This value was calculated based on the following equation and expressed as mEq per kg of the sample as shown in the Eq. (1):(1) PVmEq/kgsample=S×NW×100

where S, N, and W denote the titration volume (mL), the normality of the sodium thiosulfate solution (0.01), and sample weight, respectively (AOCS, 1980). For the determination of the thiobarbituric acid (TBARS) value, the burger sample (20 g) was blended with 950 mL of 20% trichloroacetic acid for 2 min. The blend was then filtered using a Whatman filter paper No. 1. Subsequently, 5 mL of the filtered mixture was mixed with the TBA solution (0.01 M TBA in 90% acetic acid) and kept at 100 °C for 60 min. After cooling to 25 °C, the pink mixture's absorbance was read at 532 nm using a Uv-visible spectrophotometer (Hitachi, Japan). The findings were computed using a standard curve of 1,1,3,3-tetraethoxypropane (TEP) (0.06 to 1.0 μg/mL). Malondialdehyde equivalent, or mg MDA, was used to represent the TBARS value which was presented as mg malondialdehyde (MDA) per kg of the sample (Barbosa et al., 2022).

2.7.3 Evaluation of protein oxidation

Protein oxidation was assessed based on the total carbonyl content using the method proposed by Özer and SeÇen (2018), along with several minor changes. A 2.5 g burger sample was homogenized with an 8 M urea solution for 20 s. The protein content of the mixture was then precipitated by adding 1 mL of 10% trichloroacetic acid, and the mixture underwent centrifugation at 5000 ×g for 5 min. Next, 100 μL of the homogenized sample was treated separately with 2 M hydrochloric acid (1 mL) and an equal volume of 2 M hydrochloric acid containing 0.2% w/v dinitrophenylhydrazine (DNPH).

The samples were dissolved in 20 mM sodium phosphate buffer containing 6 M guanidine hydrochloride (pH = 6.5, 1.5 mL). After stirring and centrifuging at 4200 ×g for 2 min, the absorbance was read at 280 nm. This study used bovine serum albumin as the standard. The carbonyl content of the samples is reported as nmol of DNPH per mg of protein.

2.7.4 Color assessment

The meat surface color was calculated by a colorimeter (CR-400, Konica Minolta, Japan). This study examined the color parameters, namely L* indicates lightness, a* is the red/green coordinate, and b* is the yellow/blue coordinate (Esmaeili et al., 2024).

2.7.5 Microbial evaluation

For the evaluation of the microbial load in the burger samples, a dilution of each sample was first prepared. The sample (10 g) was first blended with 0.1% sterile peptone solution (90 mL) in a stomacher and homogenized at room temperature for 1 to 2 min. The prepared serial dilutions included 10−1 to 10−6. The diluted sample (100 μL) was spread on the surface of plates containing the prepared medium. Next, the number of aerobic mesophilic and psychotropic bacteria was calculated in the plate count agar medium. The incubation of the plates was performed for 48 h and 10 days at 30 °C and 7 °C for mesophilic and psychrophilic bacteria, respectively.

The number of Enterobacteriaceae in cultured violet red bile glucose agar was determined after incubation for 24 h at 37 °C. The lactic acid bacteria (LAB) were also counted by incubating the cultured Lactobacillus MRS agar medium for 24 h at 37 °C (Memmert BE500 incubator) (Emiroğlu et al., 2010). The final microbial results were reported as log CFU/g sample.

2.7.6 Sensory evaluation

The sensory characteristics of the burger samples, including flavor, color, texture, and overall acceptability, were assessed utilizing the hedonic test with 30 panelists (an equal number of males and females aged 20–35 years). Before the sensory evaluation, the burgers were removed from the freezer and thawed in a refrigerator for 12 h. They were then cooked on a hot plate at 150 °C until the internal temperature reached 72 °C at the geometric point of each sample. Next, each cooked burgers was sliced into four parts and given to the panelists on white-coded plastic plates, along with the sensory questionnaire. The panelists rated the samples on a 9-point hedonic scale (1: strongly dislike to 9: strongly like); a minimum acceptable score of 5 was considered for each sensory parameter (Esmaeili et al., 2024).

“The study was reviewed and approved by the Science and Research Branch, Islamic Azad University IRB and informed consent was obtained from each subject prior to their participation in the study.”

2.8 Statistical analysis

All the tests on each sample were conducted in triplicate. The data were analyzed using a one-way analysis of variance with SPSS software (version 22.0). Significant differences in the mean values were examined utilizing Duncan's multiple range test at P < 0.05. Mean ± standard deviation is used to express the results.

3 Results and discussion

3.1 Phenol content and antioxidant activity of RCE

Phenolic compounds are a major group of phytochemical compounds, which can be found naturally in various plants. They include anthocyanins, phenolic acids, tannins, and flavonoids. The TPC and antioxidant activity of RCE were measured by the Folin-Ciocalteu method and DPPH radical scavenging assay, respectively. The RCE contained 4.51 mg GAE/g DW of total phenol and a remarkable phenolic compound content. Similarly, in a study by Soare et al. (2015), the TPC of RCE was 5.16 mg GAE/g DW. The RCE prepared in the study by Rovná et al. (2020) contained 2.61–6.33 mg GAE/g of total phenol. These compounds are known for their robust antioxidant properties, which are crucial in neutralizing free radicals and preventing oxidative stress. These compounds have strong free radical scavenging activity, neutralizing free radicals and preventing oxidative damage. This helps maintain the quality and shelf life of coated burgers by reducing lipid oxidation and preventing rancidity. They also inhibit enzymes essential for oxidative reactions, slowing down spoilage processes. Furthermore, they can integrate into cell membranes, altering their permeability and stabilizing cellular structures against oxidative stress. These combined actions highlight the potent antioxidant capabilities of RCE, making them valuable for extending shelf life and improving food product sensory qualities (Negrean et al., 2024). Generally, climatic conditions, harvest season, and plant maturity are important factors, which affect the amounts of bioactive compounds in extracts. On the other hand, temperature, solvent, extraction time, and extraction method are other important factors that affect the TPC of extracts. The antioxidant activity of RCE (based on IC50) was 481.69 mg/mL, underscores its efficacy in scavenging reactive oxygen species (ROS) and enhancing product stability and shelf life.

3.2 Characteristics of RCE nanoemulsions

Fig. 2A shows the mean droplet size, polydispersity index (PDI), and zeta potential of RCE nanoemulsions. The mean droplet size of RCE nanoemulsions was 28.21 nm. The PDI is one of the primary parameters determining the stability of colloidal systems, if this index is below 0.250, the system has adequate stability (Harimurti et al., 2020). Since the PDI of RCE nanoemulsions in the present study was 0.234, it had adequate stability.Fig. 2 A) The RCE-loaded nanoemulsions characteristics, B) FE-SEM images of different CSG-based edible coatings, C) FTIR spectra of CSG-based edible coatings without and with 40% RCE-loaded nanoemulsions, and D) Effect of different coatings on protein oxidation of burgers during 90-days storage at freezer.

Fig. 2

Previous studies have used the ultrasound-emulsification method for the production of nanoemulsions with small particle sizes and low PDI. The zeta potential indicates the surface charge of nanoemulsion droplets and the stability of emulsion systems (Ashrafi et al., 2024). Generally, nanoemulsions with a zeta potential above ±25 mV demonstrate remarkable stability (Wang et al., 2019). Since the zeta potential of RCE nanoemulsions was −30.14 mV, the systems were stable. Additionally, Lee et al. (2019), by producing turmeric extract nanoemulsions using the ultrasonic method, reported a zeta potential of −36.93 mV. Harimurti et al. (2021) also reported the zeta potential of nanoemulsions of temulawak and red dragon fruit extracts, prepared by the emulsification method, to be within the range of −32.0 to −38.2 mV.

3.3 Morphology of edible coatings (FE-SEM)

The structure and uniformity of the CSG-based edible coatings containing different levels of RCE were studied using FE-SEM, and the surface micrographs of the coatings are shown in Fig. 2B. As can be seen in the figure, CSG-based coating had a smooth and uniform structure and no cracks and pores were observed in the coating structure. In the coating containing 10% and 20% RCE, a smooth and uniform structure was also observed, and RCE were uniformly dispersed in the structure of the CSG-coating and showed compatibility with the coating material. The micrograph of the CSG-coating containing 40% RCE showed that RCE were mostly uniformly dispersed in the coating network and only a little accumulation was observed in some parts. In this micrograph, cracking was observed in the structure of the CSG-coating, and in order to maintain the performance of the coatings, the use of higher levels of 40% RCE is not recommended due to tearing the structure of coating. A preliminary test was conducted to choose the suitable level of RCE for coating burgers based on FE-SEM analysis, and it was observed that higher levels than 40% RCE are not suitable due to numerous small cracks in the coating structure (data not shown). The existence of cracks or holes in the structure of edible coatings and films has significant effects on their functional characteristics, such as water vapor and oxygen permeability, and mechanical properties. Yuan et al. (2022) also observed some aggregation of emulsion droplets in the SEM image of chitosan film containing W/O/W emulsion.

3.4 FTIR spectra of edible coatings

The functional groups of the CSG-based coating without and with 40% RCE were investigated using FTIR, and their spectra are shown in Fig. 2C. In the FTIR spectra of CSG-based coating, the peak in the region of 3380 cm−1 was related to the O—H groups stretching vibration (Hasheminya & Dehghannya, 2021) and shows the OH bonds between fructose and glucose in the gum (Mujtaba et al., 2019). The peak in the region of 2957 cm−1 corresponded to the C—H stretching vibrations in CH2 groups (Hasheminya & Dehghannya, 2021). The peaks in the regions of 1693 and 1521 cm−1 indicates the presence of proteins in the structure of CSG (Mujtaba et al., 2019). The peak in the region of 1023 cm−1 was related to vibration of C-O-H or C-O-C (Gheribi et al., 2018) and indicates the glycosidic bonds of carbohydrates (Mujtaba et al., 2019). In the FTIR spectra of CSG-based edible coating containing 40% RCE-loaded nanoemulsions, all the peaks in the FTIR spectra of CSG coating without nanoemelsions were present, and only a slight shift in the areas of these peaks was observed and the peak in the region of ∼3300 cm−1 became larger due to the presence of hydroxyl groups of phenolic compounds in the RCE. In the spectra of CSG-based edible coating containing 40% RCE-loaded nanoemulsions, there were also two peaks of 1821 cm−1 and 1368 cm−1 corresponded to the ester carbonyl functional group of triglycerides, and C—O stretching bonds, respectively. In general, the interactions of CSG and RCE-loaded nanoemulsions were physical. In the study of Yuan et al. (2022) also reported that no pronounced interaction was observed between the chitosan edible film and W/O/W emulsion of nisin and carvacrol in the FTIR spectra.

3.5 Burgers' pH

Table 2 shows the changes in the burger samples' pH, coated with various coating solutions within a 90-day frozen storage period. According to the findings, on the first day, the coating of burgers with CSG solutions did not bring about any significant changes in the pH of samples (P > 0.05), and the pH of the burgers was within the range of 5.31–5.35. Özogul et al. (2016) also reported consistent findings with the findings of the current investigation. They also found that the incorporation of nanoemulsions on the first day of experiments did not have any significant effects on the pH of fish and meat products. Within 90 days of storage, the burger samples' pH increased to 5.60–5.86 (P < 0.05). Since meat and meat products are rich in protein, as a result of the growth of microorganisms during storage, proteins are broken down by enzymes secreted by these microorganisms, and different alkaline compounds, such as ammonia, are produced, resulting in the elevation of the samples' pH after some time (Özogul et al., 2016). The increased pH of meat products over time has also been shown in previous studies (Ashrafi et al., 2024).Table 2 Effect of different coatings on PV, TBA and pH of burgers during 90-days storage at freezer (Mean ± SD, n = 3).

Table 2Parameters	Samples	Storage period (Day)	
1	30	60	90	
PV
(meq/kg)	C	0.34 ± 0.01 Da	0.56 ± 0.01 Ca	0.79 ± 0.03 Ba	1.00 ± 0.04 Aa	
CSG	0.34 ± 0.00 Da	0.53 ± 0.01 Cb	0.65 ± 0.01 Bb	0.82 ± 0.02 Ab	
CSG-10RCE	0.34 ± 0.02 Da	0.48 ± 0.02 Cc	0.60 ± 0.01 Bc	0.71 ± 0.04 Ac	
CSG-20RCE	0.34 ± 0.01 Da	0.45 ± 0.00 Cd	0.53 ± 0.03 Bd	0.60 ± 0.03 Ad	
CSG-40RCE	0.34 ± 0.02 Da	0.41 ± 0.02 Ce	0.47 ± 0.01 Be	0.52 ± 0.01 Ae	


	
TBA
(mg MDA/kg)	C	0.42 ± 0.02 Da	0.49 ± 0.01 Ca	0.63 ± 0.01 Ba	0.76 ± 0.03 Aa	
CSG	0.42 ± 0.00 Da	0.48 ± 0.01 Ca	0.56 ± 0.01 Bb	0.64 ± 0.02 Ab	
CSG-10RCE	0.41 ± 0.02 Da	0.47 ± 0.02 Cab	0.52 ± 0.01 Bc	0.58 ± 0.02 Ac	
CSG-20RCE	0.41 ± 0.01 Da	0.45 ± 0.01 Cb	0.49 ± 0.02 Bcd	0.52 ± 0.00 Ad	
CSG-40RCE	0.41 ± 0.01 Ca	0.44 ± 0.02 BCb	0.46 ± 0.00 ABd	0.48 ± 0.01 Ae	


	
pH	C	5.35 ± 0.02 Da	5.51 ± 0.00 Ca	5.68 ± 0.01 Ba	5.86 ± 0.01 Aa	
CSG	5.33 ± 0.02 Da	5.49 ± 0.01 Cb	5.64 ± 0.01 Bb	5.81 ± 0.01 Ab	
CSG-10RCE	5.33 ± 0.01 Da	5.46 ± 0.01 Cc	5.59 ± 0.02 Bc	5.71 ± 0.01 Ac	
CSG-20RCE	5.32 ± 0.01 Da	5.42 ± 0.01 Cd	5.54 ± 0.01 Bd	5.66 ± 0.01 Ad	
CSG-40RCE	5.31 ± 0.02 Da	5.38 ± 0.01 Ce	5.49 ± 0.01 Be	5.60 ± 0.02 Ae	
Values with a different small letter of the same storage day are significantly different and values with large different letter of the same treatment are significantly different (P < 0.05).

The active CSG coatings, especially coating solutions containing RCE nanoemulsions, by reducing the growth rate of microorganisms and thereby decreasing the degradation of proteins, could reduce the intensity of pH changes during storage in comparison to the control sample without coating. Moreover, increasing the level of RCE nanoemulsions in the coating solutions reduced pH changes over time, significantly (P < 0.05), which is associated with the enhanced antimicrobial activity of coatings. In this regard, Abdou et al. (2018) reported that pectin coatings containing nanoemulsions of curcumin decreased the increasing rate of pH in chicken fillet samples throughout the storage duration; they also ascribed these observations to the antibacterial activity of the used coatings. Decreased pH changes in ostrich meat were also observed over time owing to the use of an edible coating based on Qodume Shirazi seed mucilage, holding lavender essential oil (Heydari et al., 2020).

3.6 Lipid oxidation of burgers

The oxidation of lipids is a major destructive process, which can have adverse effects on the color and flavor of food products and result in toxic by-product accumulation in food. One of the primary objectives of the food industry is to reduce the oxidation rate and maintain food quality during storage. Peroxides, as the major products of lipid oxidation, are unstable and break down; they produce secondary oxidation products (Ashrafi et al., 2018). The primary products of lipid oxidation are measured by PV. The TBA is utilized to measure the secondary products of lipid oxidation. Therefore, in this study, the oxidation stability of the burger samples coated with different CSG solutions in 90 days of freezer storage was determined by measuring the PV and TBA; Table 2 shows the results. The PV and TBA values of burger samples on the first day were 0.34 mEq/kg and 0.41–0.42 mg MDA/kg samples, respectively. The coating samples had no significant (P > 0.05) effects on the oxidation indices of the burgers.

The storage time had a remarkable impact on burgers' lipid oxidation (P < 0.05). Over time, the PV and TBARS of different burger samples gradually increased. However, the rate of increase in the uncoated sample (control) was significantly higher than in the coated sample, and the highest values of PV (1.00 mEq/kg sample) and TBA (0.76 mg MDA/kg sample) were reported in the control sample on the final day of storage. During the 30, 60, and 90-day storage periods, a significant difference in PV and TBA were observed across all samples (P < 0.05), indicating that storage duration directly influences the increase in PV and TBA for all samples (except TBA sample CSG-40RCE on days 60 and 90). Additionally, there was a significant difference (P < 0.05) between the samples at each specific time point of measurement (excluding the initial day). This demonstrates that the coating, the incorporation of nanoemulsion into the coating, and the increased concentration of nanoemulsion all have a direct impact on elevating the PV value. Edible coatings are generally protective layers on food products that can reduce the impact of environmental conditions on coated foods and reduce the oxidation process by decreasing the level of oxygen available to food products, as oxygen is one of the main promoters of oxidation. On the other hand, in previous studies, chia seeds have been introduced as rich sources of major synergistic antioxidant compounds, such as chlorogenic acids, flavonoids, caffeic acid, quercetin, myricetin, kaempferol, tocopherols, carotenoids, and phytosterols, which can slow down the oxidation process of food products and increase their shelf-life (Eslamian Amiri et al., 2021).

The incorporation of RCE-loaded nanoemulsions and the increase in their level also significantly increased (P < 0.05) the antioxidant activity of CSG coatings and reduced the production rate of primary and secondary products of lipid oxidation; therefore, on day 90, the burgers coated with CSG solutions containing 40% RCE (CSG-40RCE) had the lowest PV and TBARS (0.52 mEq/kg sample and 0.48 mg MDA/kg sample, respectively). Overall, meat and meat products with TBARS values <1 mg MDA/kg sample were considered fresh products (Esmaeili et al., 2020). Based on the current study's results, all the burger samples were acceptable regarding lipid oxidation until the last day of the frozen storage period.

Previous research has shown that active coatings containing extracts abundant in phenolic compounds can significantly decrease the lipid oxidation rate of meat and meat products (Ruan et al., 2019). Phenolic compounds are generally known as potential antioxidant and antiradical compounds that can donate hydrogen to unstable free radicals and block the oxidation process. The antioxidant activity of these bioactive compounds also depends on scavenging reactive nitrogen and oxygen species, chelating metals (especially Cu and Fe), reducing oxidized intermediates, activating antioxidant enzymes (e.g., superoxide dismutase and catalase), and inhibiting the function of oxidase and peroxidase enzymes (Zhang et al., 2020).

3.7 Protein oxidation of burgers

Fig. 2D depicts the protein oxidation of various burger samples during the 90-day frozen storage period. On the first day of the experiments, different burger samples did not significantly differ (P > 0.05) in the carbonyl content (1.00–1.01 nmol/mg protein). During the storage time, on account of protein oxidation, the amount of carbonyl increased in the burger samples (P < 0.05). Moreover, increased protein oxidation in the burger and ground beef samples throughout the storage duration has been shown by Trujillo-Mayol et al. (2021) and Amiri et al. (2019), respectively. However, the carbonyl production rate was the highest in the control sample and then in the sample coated with CSG solution in comparison to the other samples; the carbonyl content of these samples was 2.47 and 2.14 nmol/mg protein on the final day of storage, respectively; nevertheless, in samples coated with CSG solutions containing 10%, 20%, and 40% RCE nanoemulsions, the corresponding values were 1.62, 1.51, and 1.40 nmol/mg protein, respectively. Generally, research has confirmed that phenolic compounds contain free hydroxyl groups and can prevent further oxidation of –SH groups in the protein structure. These antioxidant compounds reduce the production of carbonyl in the samples (Ashrafi et al., 2024). These antioxidant compounds reduce the production of carbonyl in the samples. In agreement with the findings of the current study, a study by Amiri et al. (2019) demonstrated a decrease in the protein oxidation of beef patty covered with edible films based on corn starch containing Zataria multiflora essential oil in comparison to the control sample. Jongberg et al. (2013) also agreed that rosemary and green tea extracts could significantly reduce protein oxidation in sausage samples in comparison to the control sample.

3.8 Color analysis of burgers

Table 3 shows the results of the investigation of color parameters in different burger samples. The results indicated that coating samples with CSG solutions containing different levels of RCE nanoemulsions led to a decrease in L* values and caused an increase in the a* and b* values of burgers (P < 0.05). As the concentration of RCE nanoemulsions in the coating solutions increased, the brightness of the samples decreased; nevertheless, the redness and yellowness increased.Table 3 Effect of different coatings on color parameters of burgers during 90-days storage at freezer (Mean ± SD, n = 3).

Table 3Parameters	Samples	Storage period (Day)	
1	30	60	90	
L*	C	56.67 ± 0.11 Aa	55.27 ± 0.13 Bab	54.16 ± 0.16 Cc	52.80 ± 0.37 Dc	
CSG	56.51 ± 0.32 Aab	55.27 ± 0.11 Bab	54.54 ± 0.05 Cb	53.49 ± 0.25 Db	
CSG-10RCE	56.11 ± 0.28 Ab	55.43 ± 0.17 Ba	54.84 ± 0.10 Ca	54.32 ± 0.31 Da	
CSG-20RCE	55.45 ± 0.09 Ac	55.00 ± 0.25 Bbc	54.64 ± 0.13 Bab	54.10 ± 0.07 Ca	
CSG-40RCE	54.85 ± 0.16 Ad	54.74 ± 0.06 Ac	54.56 ± 0.22 Aab	54.12 ± 0.07 Ba	


	
a*	C	11.86 ± 0.10 Ad	11.09 ± 0.04 Be	10.46 ± 0.10 Ce	10.05 ± 0.10 De	
CSG	11.98 ± 0.03 Ad	11.48 ± 0.11 Bd	11.07 ± 0.06 Cd	10.63 ± 0.05 Dd	
CSG-10RCE	12.57 ± 0.09 Ac	12.26 ± 0.17 Bc	11.99 ± 0.18 BCc	11.76 ± 0.14 Cc	
CSG-20RCE	13.41 ± 0.16 Ab	13.29 ± 0.09 ABb	13.13 ± 0.10 BCb	12.94 ± 0.12 Cb	
CSG-40RCE	14.30 ± 0.06 Aa	14.24 ± 0.05 Aa	14.15 ± 0.13 ABa	13.96 ± 0.08 Ba	


	
b*	C	15.11 ± 0.08 De	15.98 ± 0.07 Cd	16.50 ± 0.05 Bc	17.62 ± 0.14 Aa	
CSG	15.37 ± 0.13 Dd	15.84 ± 0.09 Cd	16.27 ± 0.04 Bd	17.30 ± 0.04 Ab	
CSG-10RCE	15.83 ± 0.04 Dc	16.13 ± 0.05 Cc	16.73 ± 0.06 Bb	17.20 ± 0.07 Abc	
CSG-20RCE	16.10 ± 0.06 Db	16.33 ± 0.05 Cb	16.81 ± 0.05 Bb	17.09 ± 0.10 Ac	
CSG-40RCE	16.68 ± 0.04 Ca	16.94 ± 0.08 Ba	17.13 ± 0.09 ABa	17.24 ± 0.06 Abc	
Values with a different small letter of the same storage day are significantly different and values with large different letter of the same treatment are significantly different (P < 0.05).

Regarding the amount of brightness (L*) of each sample, a significant difference was observed between 30, 60 and 90 days of storage (except for the CSG-40RCE sample until the 60th day) (P < 0.05), which shows that the time of direct storage has an effect on reducing The L* amount is for all samples. The non-significance of L* in the CSG-40RCE sample until the 60th day shows that the active coating containing nanoemulsion has been able to remove the effective effects on turbidity. The effect of the coating variables at a fixed measurement time shows that the CSG coating alone had no statistically significant effect (P < 0.05), but with the increase of nanoemulsion to the coating, and the increase of the concentration of nanoemulsion, a direct effect on the reduction of brightness is observed. This statistical difference was observed on the 30th day only in the case of CSG-40RCE, on the 60th day between the control with all treatments, and on the 90th day between the treatments containing nanoemulsion with CSG coating and the control. Regarding the redness (a*) and yellowness (b*) of the samples, respectively, the decrease of a* (increase of greenness) and the increase of b* (increase of blueness) were significant (p < 0.05) in the all storage times. An increase of both parameters were observed among the experimental treatments. The color changes caused by the coating of burgers were attributed to the intrinsic color of RCE. The L*, a*, and b* values of the control sample were 56.67, 11.86, and 15.31 on the last day, respectively. In samples coated with CSG solutions containing different levels of RCE nanoemulsions, the corresponding values were 54.85–56.11, 12.57–14.30, and 15.83–16.68, respectively. During the 90-day frozen storage time, the L* and a* values of the burger samples gradually decreased; however, the b* value increased (P < 0.05). The changes in the color of meat and meat products over time are often related to the oxidation process and protein denaturation (Ashrafi et al., 2024).

Evidence suggests that primary and secondary products of lipid oxidation, along with reactive oxygen species, can oxidize Fe2+ to Fe3+ in oxymyoglobin, leading to the production of metmyoglobin. This process contributes to the reduced redness intensity of meat and meat products over time (Elhadef et al., 2020). However, coating burgers with CSG solutions, especially those containing high levels of RCE nanoemulsions, improved color maintenance and reduced the intensity of color changes over time. This improvement is related to the significant antioxidant activity of the active coatings used in the current study.

Additionally, it demonstrated that the a* index of beef burgers decreased slightly during the storage time, which was attributed to lipid oxidation. In agreement with the findings of the current study, Ghaderi-Ghahfarokhi et al. (2017) showed that cinnamon oil-chitosan nanoemulsions increased the stability of beef patty color. Other studies have also reported the color preservation of meat products by coating them with active solutions containing different extracts (Ruan et al., 2019).

3.9 Microbial load of burgers

Meat and meat products generally contain a high moisture content and nutrients. They also have a moderate pH and are consequently suitable substrates for growth on microorganisms, mainly bacteria; they are also easily spoiled (Das et al., 2019). Table 4 shows the analysis of the total viable count (TVC), psychotropic count (PTC), Enterobacteriaceae count, and the LAB of the burger samples coated with different CSG solutions during a 90-day frozen storage period. Based on the obtained findings, on the first day, different burger samples did not differ significantly (P > 0.05) in the microbial load, and the TVC, PTC, Enterobacteriaceae, and LAB counts were 3.41–3.44, 3.03–3.05, 2.44–2.46, and 2.35–2.36 log CFU/g sample in the burgers, respectively.Table 4 Effect of different coatings on microbial load (log CFU/g) of burgers during 90-days storage at freezer ((Mean ± SD, n = 3).

Table 4Microorganisms	Samples	Storage period (Day)	
	1	30	60	90	
TVC
(log CFU/g)	C	3.43 ± 0.06 Da	4.51 ± 0.11 Ca	5.16 ± 0.08 Ba	6.35 ± 0.10 Aa	
CSG	3.44 ± 0.04 Da	4.17 ± 0.09 Cb	4.78 ± 0.14 Bb	5.95 ± 0.05 Ab	
CSG-10RCE	3.42 ± 0.05 Da	4.03 ± 0.06 Cc	4.32 ± 0.05 Bc	4.99 ± 0.03 Ac	
CSG-20RCE	3.41 ± 0.04 Da	3.89 ± 0.07 Cd	4.18 ± 0.08 Bd	4.79 ± 0.09 Ad	
CSG-40RCE	3.41 ± 0.06 Da	3.62 ± 0.10 Ce	3.84 ± 0.06 Be	4.43 ± 0.09 Ae	


	
PTC
(log CFU/g)	C	3.05 ± 0.02 Da	3.96 ± 0.01 Ca	4.74 ± 0.05 Ba	5.64 ± 0.07 Aa	
CSG	3.05 ± 0.04 Da	3.91 ± 0.03 Ca	4.25 ± 0.08 Bb	5.17 ± 0.11 Ab	
CSG-10RCE	3.05 ± 0.04 Da	3.78 ± 0.06 Cc	4.09 ± 0.03 Bc	4.40 ± 0.05 Ac	
CSG-20RCE	3.03 ± 0.03 Da	3.55 ± 0.03 Cd	3.91 ± 0.06 Bd	4.25 ± 0.07 Ad	
CSG-40RCE	3.03 ± 0.02 Da	3.39 ± 0.07 Ce	3.66 ± 0.05 Be	3.98 ± 0.09Ae	


	
Enterobacteriaceae
(log CFU/g)	C	2.45 ± 0.05 Da	3.34 ± 0.03 Ca	3.58 ± 0.05 Ba	3.66 ± 0.01 Aa	
CSG	2.44 ± 0.03 Da	3.21 ± 0.02 Cb	3.46 ± 0.02 Bb	3.58 ± 0.04 Ab	
CSG-10RCE	2.46 ± 0.03 Da	2.94 ± 0.02 Cc	3.11 ± 0.06 Bc	3.30 ± 0.07 Ac	
CSG-20RCE	2.45 ± 0.03 Da	2.89 ± 0.04 Cd	2.95 ± 0.01 Bd	3.05 ± 0.04 Ad	
CSG-40RCE	2.45 ± 0.06 Da	2.71 ± 0.03 Ce	2.83 ± 0.04 Be	2.92 ± 0.03 Ae	


	
LAB
(log CFU/g)	C	2.36 ± 0.01 Da	3.08 ± 0.01 Ca	3.38 ± 0.07 Ba	4.17 ± 0.02 Aa	
CSG	2.35 ± 0.06 Da	2.96 ± 0.01 Cb	3.25 ± 0.03 Bb	4.02 ± 0.06 Ab	
CSG-10RCE	2.35 ± 0.09 Da	2.83 ± 0.01 Cc	3.10 ± 0.05 Bc	3.35 ± 0.09 Ac	
CSG-20RCE	2.36 ± 0.03 Da	2.71 ± 0.02 Cd	2.94 ± 0.03 Bd	3.09 ± 0.02 Ad	
CSG-40RCE	2.36 ± 0.04 Da	2.55 ± 0.07 Ce	2.79 ± 0.05 Be	3.01 ± 0.02 Ae	
Values with a different small letter of the same storage day are significantly different and values with large different letter of the same treatment are significantly different (P < 0.05).

In all the burger samples, there was an increase in the count of different bacteria in the frozen storage time (P < 0.05); however, the coating of burgers with CSG solutions, especially solutions containing RCE nanoemulsions, remarkably decreased the growth rate of bacteria in the treated samples, compared to the control sample (P < 0.05). In general, edible coatings can reduce oxygen exchange; therefore, they can limit the growth of microorganisms (Esmaeili et al., 2024).

Lad et al. have also investigated the antibacterial activity of CSG (Lad et al., 2020). By increasing the concentration of RCE nanoemulsions in the coating solutions, due to an increase in the phenolic content, the count of bacteria also indicated a remarkable reduction (P < 0.05). On the final day of storage, the lowest TVC (4.43 log CFU/g), PTC (3.98 log CFU/g), Enterobacteriaceae (2.92 log CFU/g), and LAB (3.01 log CFU/g) counts were noticed in the sample coated with CSG solution containing 40% RCE; nevertheless, the highest counts were reported in the control sample (6.35, 5.64, 3.66, and 4.17 log CFU/g, respectively). The maximum recommended count for the TVC in meat and meat products is 7 log CFU/g sample (Huang et al., 2014). All the studied burgers had a microbial load lower than the maximum acceptable level until the final day of storage.

Herbal extracts generally contain a mixture of different phenolic compounds that have synergistic effects and remarkable antimicrobial activity against various microorganisms. Phenolic compounds can affect protein biosynthesis, interfere with bacterial metabolic processes, and inhibit the synthesis of DNA and ATP. The antimicrobial activity of phenolic compounds depends on their molecular form and the susceptibility of bacterial strains (Efenberger-Szmechtyk et al., 2021). Additionally, Eslamian Amiri et al. (2021) showed bacterial growth in the coating of quail fillets with chitosan-CSG solutions, especially coating solutions containing Bay laurel essential oil liposomes. Moreover, a study by Liu et al. (2021) showed that chitosan nanoemulsion coating containing eugenol (i.e., a bioactive compound) exhibited greater preservative activities on the hairtail than the coating based on chitosan nanoemulsion alone. The utilization of edible coating on the basis of chitosan and gelatin containing tarragon essential oil nanocapsules could also significantly reduce the growth of the TVC in pork slices during storage (Zhang et al., 2020).

The phenolic compounds in RCE disrupt microbial cell walls and interfere with metabolic processes, leading to cell death and enhancing the safety and shelf life of coated burgers. The effectiveness of RCE is further amplified by the use of a nanoemulsion delivery system, which consists of fine oil-in-water emulsions with droplet sizes typically ranging from 20 to 200 nm (Negrean et al., 2024). This delivery system offers multiple advantages: it increases the bioavailability of phenolic compounds by improving their solubility and stability, ensuring maximum interaction with microbial cells and free radicals. Additionally, the nanoemulsion allows for controlled release, maintaining the efficacy of the phenolic compounds over time and providing sustained protection against oxidation and microbial growth. The small droplet size facilitates deeper penetration of bioactive compounds into food matrices, leading to more uniform distribution of antioxidants and antimicrobial agents within the food product (Gorzin et al., 2024). Furthermore, nanoemulsions protect sensitive compounds from environmental degradation caused by light, heat, and oxygen, thereby prolonging the functional life of phenolic compounds and ensuring their effectiveness throughout the shelf life of the coated burgers. This combination of antimicrobial properties and advanced delivery mechanisms highlights the potential of RCE nanoemulsions in enhancing food preservation and safety.

3.10 Sensory evaluation

Sensory properties are significant parameters in the acceptance of food products by consumers. Therefore, treatments should maintain the sensory quality of foods during storage without any adverse effects on the sensory features of products when applied. Table 5 shows the analysis of the sensory properties of burger samples coated with CSG solutions containing RCE-loaded nanoemulsions. As shown in this table, on the first day, the coating of burgers with different CSG-based solutions did not have any adverse effects on the sensory features of the samples. In the course of the 90 frozen storage days, all the samples showed a slight decrease (P < 0.05) in the sensory scores; nevertheless, using active coatings could maintain the sensory quality of the burger samples over time. The characteristics of flavor, color and texture in the control and CSG coated samples were directly affected by the time of storage because there was a statistically significant difference between the parameters in all days of storage (p < 0.05). However, the addition of nanoemulsion to the coating was able to compensate for the negative effect of the storage time, so that no statistically significant difference was observed in the taste of the CSG-40RCE sample at different storage times. Regarding the color parameter, only increasing the amount of nanoemulsion by 20% could compensate for the negative effect of storage time.Table 5 Effect of different coatings on sensory properties of burgers during 90-days storage at freezer ((Mean ± SD, n = 3).

Table 5Parameters	Samples	Storage period (Day)	
	1	30	60	90	
Flavor	C	7.33 ± 0.28 Ab	6.00 ± 0.00 Bd	5.18 ± 0.34 Cc	4.33 ± 0.28 De	
CSG	7.00 ± 0.00 Ab	6.33 ± 0.28 Bc	6.00 ± 0.00 Cb	5.66 ± 0.21 Dd	
CSG-10RCE	8.00 ± 0.00 Aa	7.66 ± 0.21 Bb	7.33 ± 0.28 Ba	6.00 ± 0.00 Cc	
CSG-20RCE	8.18 ± 0.34 Aa	7.66 ± 0.21 Bb	7.18 ± 0.34 Ba	6.50 ± 0.25 Cb	
CSG-40RCE	8.00 ± 0.00 Aa	8.33 ± 0.28 Aa	7.84 ± 0.34 ABa	7.33 ± 0.28 Ba	


	
Color	C	8.33 ± 0.28 Ab	6.66 ± 0.21 Bd	5.33 ± 0.28 Cd	4.00 ± 0.00 De	
CSG	8.33 ± 0.28 Ab	7.66 ± 0.21 Bc	7.00 ± 0.00 Cc	6.00 ± 0.00 Dd	
CSG-10RCE	8.66 ± 0.21 Ab	8.00 ± 0.00 Bb	7.18 ± 0.34 Cbc	6.50 ± 0.25 Dc	
CSG-20RCE	8.75 ± 0.28 Aab	8.33 ± 0.28 Aa	7.50 ± 0.29 Bab	7.00 ± 0.00 Cb	
CSG-40RCE	9.00 ± 0.00 Aa	8.50 ± 0.29 Ba	8.18 ± 0.34 Ca	7.50 ± 0.25 Da	


	
Texture	C	8.50 ± 0.25 Aa	6.66 ± 0.21 Be	5.33 ± 0.28 Cd	4.50 ± 0.25 De	
CSG	7.66 ± 0.21 Ab	7.00 ± 0.00 Bd	6.00 ± 0.00 Cc	5.66 ± 0.21 Dd	
CSG-10RCE	7.86 ± 0.21 Ab	7.33 ± 0.28 ABc	6.84 ± 0.34 Bb	6.00 ± 0.00 Cc	
CSG-20RCE	7.86 ± 0.21 Ab	8.00 ± 0.00 Ab	7.33 ± 0.28 Bab	7.00 ± 0.00 Cb	
CSG-40RCE	8.00 ± 0.00 Ab	8.33 ± 0.28 Aa	7.50 ± 0.25 Ba	7.50 ± 0.25 Ba	


	
Overall acceptability	C	8.33 ± 0.28 Aab	6.50 ± 0.25 Be	5.50 ± 0.25 Cd	4.33 ± 0.28 De	
CSG	7.90 ± 0.16 Ab	7.00 ± 0.00 Bd	6.66 ± 0.21 Cc	6.00 ± 0.00 Dd	
CSG-10RCE	7.90 ± 0.16 Ab	7.33 ± 0.28 Bc	7.00 ± 0.00 Cb	6.33 ± 0.28 Dc	
CSG-20RCE	8.33 ± 0.28 Aab	8.00 ± 0.00 Bb	7.84 ± 0.34 Ba	7.00 ± 0.00 Cb	
CSG-40RCE	8.66 ± 0.21 Aa	8.33 ± 0.28 ABa	7.75 ± 0.28 BCa	7.50 ± 0.25 Ca	
Values with a different small letter of the same storage day are significantly different and values with large different letter of the same treatment are significantly different (P < 0.05).

As previously mentioned, oxidation and microbial growth are two major factors that significantly affect the quality of meat products. Therefore, they can decrease the sensory scores of products during storage. Since CSG coatings, especially those containing RCE nanoemulsions, reduce oxidation and microbial growth compared to the control sample, they can better maintain the sensory quality of burgers during storage. By increasing the RCE nanoemulsion concentration in the coating, due to an increase in antioxidant and antimicrobial activities, the sensory properties of burgers could be better maintained. In this regard, Ansarian et al. (2022) showed that coated camel meat nanoemulsion-based basil seed gum film containing resveratrol and clove essential oil had greater sensory characteristics than the control sample. Amiri et al. (2019) also observed that coating beef patty with Zataria multiflora essential oil and cinnamaldehyde nanoemulsion-loaded starch films did not have a negative effect on the taste, color, odor, or the overall acceptability of the samples. Generally, because the burger samples were stored under freezing conditions, and temperature significantly affects destructive reactions, all the samples, even the control sample, were acceptable in terms of sensory features, including flavor, color, texture, and total acceptability, until the final day of this study.

4 Conclusion

Based on the findings of the current study, active CSG coatings containing RCE nanoemulsions were effective in preserving the color and sensory quality of burgers during frozen storage. The use of active coatings delayed lipid and protein oxidation and significantly reduced bacterial growth compared to the control sample. There was a direct positive relationship between the concentration of RCE nanoemulsions and the antioxidant and antimicrobial activities of the CSG coatings. Consequently, the highest antioxidant and antimicrobial effects were observed in burgers coated with the CSG solution containing the highest level of RCE nanoemulsions. This sample was identified as the most effective in the current study. Based on the study results, the recommended time to store (freeze) burgers before eating is up to 90 days. This recommendation is supported by various analyses including pH changes, oxidation stability, protein oxidation, color stability, microbial load, and sensory evaluation, all of which demonstrated that the burgers, particularly those coated with CSG solutions containing RCE nanoemulsions, maintained acceptable quality and safety parameters throughout the 90-day frozen storage period.

CRediT authorship contribution statement

Azam Ashrafi: Writing – review & editing, Writing – original draft, Software, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization. Hamed Ahari: Supervision, Data curation. Gholamhassan Asadi: Investigation, Data curation. Abdorreza Mohammadi Nafchi: Data curation, Conceptualization.

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.

There is no conflict of interest between the authors, this research was done without any funding.

Data availability

Data will be made available on request.

Acknowledgment

Special thanks to Nano Research Laboratory (Ultrasonic section),Science and Research Branch, Islamic Azad University (https://ultrasoniclab.srbiau.ac.ir).
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