Synergistic antibacterial system for beef preservation: alginate/carboxymethyl cellulose aerogel‐loaded with oregano essential oil

Abstract

BACKGROUND

As an important protein source for consumers, meat is susceptible to microbial contamination during transportation and storage, leading to spoilage and significant food waste. To address this challenge, this study aimed to develop a synergistic antibacterial system to enhance meat preservation efficacy, focusing on the design of a sodium alginate/carboxymethyl cellulose composite aerogel incorporated with oregano essential oil (OEO).

RESULTS

Structural characterization results showed that the prepared sodium alginate/carboxymethyl cellulose–OEO composite aerogel exhibited an excellent porous structure, high water absorption capacity, and favorable thermal stability. When placed beneath beef samples, the aerogel exerted dual functions of absorbing excess exudate and enabling sustained release of OEO. Antibacterial and antioxidant assays revealed that the C/A‐4% and C/A‐8% aerogel groups demonstrated remarkable synergistic antibacterial activity and antioxidant capacity. Further beef preservation tests confirmed that the aerogel system effectively maintained beef quality by synergistically inhibiting microbial proliferation, retarding protein oxidation, and mitigating lipid oxidation.

CONCLUSION

This study successfully developed a novel preservation system based on an aerogel–OEO synergistic antibacterial strategy. The sodium alginate/carboxymethyl cellulose–OEO composite aerogel integrates the dual advantages of physical exudate absorption and sustained bioactive OEO release, which can effectively inhibit microbial growth and proliferation, thereby significantly extending the shelf life of beef. Overall, this composite aerogel system demonstrates considerable potential for application in beef preservation. © 2026 Society of Chemical Industry.

INTRODUCTION

Meat serves as a vital dietary protein source, and its freshness and safety are critically compromised by microbial contamination during slaughter, processing, storage, transportation, and retail. Under favorable temperatures, spoilage manifests rapidly through textural degradation (slime formation), off‐odor production, discoloration, and accumulation of malodorous metabolites. ¹ Concurrently, lipid and protein oxidation generate reactive oxygen species (ROS) and peroxides, further deteriorating flavor, water‐holding capacity, tenderness, and nutritional value. ² These diverse quality deterioration factors point to the immediate necessity for novel conservation methods to guarantee meat security and enhance its shelf life. The Food and Agriculture Organization (FAO) reports that roughly 20% of global meat production undergoes annual loss attributable to spoilage. Conventional preservation approaches like refrigeration and chemical additives offer partial solutions, but their high energy consumption and potential health hazards have raised consumer safety concerns. ³ Consequently, the development of novel, efficient, and safe preservation materials represent a critical research frontier in meat preservation.

In recent years, aerogel‐based absorbent pads have emerged as a promising solution for fresh meat preservation,^{4, 5} demonstrating superior performance by rapidly sequestering exudate to maintain a dry microenvironment, thereby inhibiting microbial proliferation and extending shelf life. Recent research demonstrates that incorporating antimicrobial/antioxidant agents – such as curcumin, anthocyanins, cinnamon essential oil, and silver nanoparticles – can further enhance aerogel efficacy.^{6, 7, 8} However, the existing absorbent pads still have certain limitations in application, such as unsafe component sources, insufficient structural stability, and poor performance. Therefore, developing new aerogel materials with continuous antibacterial and antioxidant functions and stable structures holds significant practical significance.

Among these, oregano essential oil (OEO) has been considered as a particularly promising additive, exhibiting broad‐spectrum antimicrobial activity and strong antioxidant capacity in meat preservation applications. OEO, extracted from oregano leaves, serves as a natural hydrophobic antimicrobial and antioxidant agent.^{9, 10} It is commonly applied in preparing active packaging materials. As a food additive, it is considered safer and has gained popularity in meat preservation. However, OEO's practical application is severely hampered by its high volatility and susceptibility to degradation by light, temperature, oxygen, and ultraviolet radiation, ¹¹ which compromise its biological activity and diminish long‐term efficacy. These factors can compromise the biological activity of OEOs and diminish their antibacterial and antioxidant properties. To overcome volatility and improve matrix compatibility, OEO can be effectively encapsulated within Pickering emulsions stabilized. This approach would enhance the compatibility between OEO and the aerogel matrices as well as long‐term antibacterial performance. ¹²

Sodium alginate (SA), a type of natural polysaccharide substance, offers exceptional biocompatibility and biodegradability as a natural product. ¹³ Its widespread availability, low cost, and non‐toxic properties make it an ideal sustainable matrix for developing advanced food packaging materials, particularly in meat preservation applications. ¹⁴ Carboxymethyl cellulose (CMC), rich in hydroxyl groups, exhibits excellent water absorption capacity and forms robust hydrogen bonds with SA chains. This intermolecular crosslinking markedly improves mechanical properties, structural stability, and swelling resistance of the hydrogel network, providing a mechanically stable platform for controlled‐release applications in meat preservation. ¹⁵ Research on functional‐agent‐loaded aerogels for meat preservation remains scarce. Moreover, SA and CMC have attracted considerable attention because of their environmentally friendly, biodegradable, and non‐toxic properties, showing great potential as candidates for developing novel active and intelligent packaging materials. Despite the established research foundation on SA/CMC composites for food packaging, studies investigating their integration with Pickering‐emulsion‐stabilized essential oils for active component loading remain remarkably limited.

This study focused on creating a functional aerogel with favorable physical structure and antimicrobial–antioxidant capacity for beef preservation (Fig. 1), enhanced OEO stability, and compatibility through Pickering emulsion encapsulation, mitigating volatility while improving dispersion within the hydrophilic aerogel matrix. A synergistic matrix design utilizing SA–CMC hydrogen‐bonding interactions was used to create a mechanically robust, highly absorbent, and biodegradable scaffold. Comprehensive performance validation was carried out through systematic characterization of microstructure, mechanical properties, water absorption capacity, antioxidant/antimicrobial activities, and in situ beef preservation efficacy. The fabricated aerogels were characterized using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and mechanical testing, while their antioxidant and antibacterial activities were evaluated via 1,1‐diphenyl‐2 picryl hydrazyl (DPPH) assay and zone inhibition tests, respectively. Finally, the practical efficacy in maintaining beef quality during simulated retail storage was assessed through monitoring microbial growth, lipid oxidation, and physicochemical parameters. This integrated approach establishes a promising platform for developing next‐generation active packaging materials that combine enhanced safety, sustainability, and functional performance.

Figure 1.

Schematic of the preparation and application of aerogel. SA, sodium alginate; CMC, carboxymethyl cellulose; OEO, oregano essential oil.

MATERIALS AND METHODS

Materials

OEO was acquired from Baiye Co., Ltd (Ji'an, China). Sodium CMC was obtained from Sinopharm Chemical Reagent Co., Ltd (Shanghai, China). SA (chemical purity) was purchased from Solarbio Science & Technology Co., Ltd (Beijing, China). DPPH free radicals were supplied by TCI Development Co., Ltd (Shanghai, China). Mueller–Hinton Agar (MHA) and Mueller–Hinton Broth (MHB) were purchased from Qingdao Hope Bio‐Technology Co., Ltd (Qingdao, China). Plate count agar was sourced from Beijing Land Bridge Technology Co., Ltd (Beijing, China).

Preparation of oregano essential oil Pickering emulsion

Oregano essential oil Pickering emulsion (OEOP) was synthesized in accordance with the methodology by Li et al. ¹⁶ Briefly, chitosan nanoparticles were prepared by dissolving 0.75 wt% chitosan in 1% acetic acid solution, and then adding sodium tripolyphosphate dropwise under magnetic stirring. Subsequently, OEO was incorporated into the chitosan nanoparticles, and the mixture was exposed to ultrasonic processing for 20 min to obtain OEOP.

Preparation of aerogel

In brief, 1.5 g of sodium CMC and SA were individually dissolved in 100 mL of deionized water under magnetic stirring until complete dissolution. Subsequently, the CMC and SA solutions were mixed to prepare the CMC–SA solution. OEOP was slowly added dropwise to the CMC–SA solution and stirred magnetically for 12 h to achieve OEOP contents of 0%, 2%, 4%, and 8%, respectively. Finally, the mixtures were poured into molds (diameter: 90 mm), frozen at −80 °C for 24 h, and lyophilized for 36 h to obtain the final aerogels. The hydrogels with different OEOP contents were designated as C/A‐0, C/A‐2%, C/A‐4%, and C/A‐8%, respectively.

Physical and chemical properties of the aerogels

FTIR analysis

An FTIR spectrometer (Bruker, Ettlingen, Germany) was used to analyze the structural characteristics of the aerogel. The aerogel was frozen in liquid nitrogen, powdered, mixed with KBr, and pressed into tablets. Spectra were scanned from 400 to 4000 cm⁻¹ at a resolution of 4 cm⁻¹.

SEM analysis

The microstructure of the aerogel was observed by SEM(FlexSEM1000, Hitachi, Japan). The freeze‐dried aerogel was brittle‐fractured into small pieces with a thickness of <1 mm by liquid nitrogen, and then directly placed on the sample holder. SEM images were acquired at an acceleration voltage of 10 kV. Image J software was used for analyzing the SEM images and determining the pore size distribution.

Thermal stability analysis

Thermal stability of the aerogel was analyzed by differential scanning calorimetry (DSC; TA Instruments, USA). Approximately 3 mg of the aerogel was placed in an aluminum crucible and sealed, with a sealed empty aluminum crucible serving as the reference. The measurement was performed at a heating rate of 10 °C min⁻¹ over a temperature range of 50–200 °C, with nitrogen gas purged at 50 mL min⁻¹.

Porosity analysis

The ethanol displacement method was employed to assess the porosity of the aerogel. The initial weight of the aerogel sample was measured and denoted as M ₁. The aerogel was then placed in anhydrous ethanol, and ultrasonic assistance was used to rapidly fill the pores of the aerogel with anhydrous ethanol. The weight was measured after the ethanol fully infiltrated the pores (M ₂). The porosity was evaluated according to the following formula:

$$\begin{array}{c}\text{Porosity}\left(\%\right)=\left(1-M_1/M_2\right)\times 100\end{array}$$ (1)

Mechanical properties

The strength and texture characteristics of the aerogels were measured using a TA‐XT PLUS/50 texture analyzer (Stable Micro Systems Ltd, UK). A cylindrical probe with a diameter of 36 mm was selected for the compression test, which was performed based on the sample size. All measurements were conducted in a controlled manner with consistent pre‐test, test, and post‐test speeds set at 1.0 mm s⁻¹. The compression ratio was set at 70%, with a trigger force of 5 kg. The test was performed for two cycles with an interval of 5 s.

Water absorption analysis

The water absorption capacity of the aerogels was assessed using the gravimetric technique. The initial weight (W₁) of the dry aerogel was accurately weighed, then fully submerged in a 100‐mL pure water‐filled beaker. The aerogel was taken out and excess water removed after 2 h. The weight of the water‐absorbed aerogel (W₂) was then measured. The water absorption ratio was calculated using the formula below:

$$\begin{array}{c}\begin{array}{c}\text{Water absorbent ratio}\left(\%\right)=\left(W_2-W_1\right)/W_1\times 100\end{array}\end{array}$$ (2)

Cumulative release rates of OEO‐loaded aerogels

The release behavior of OEO was investigated using a method modified from that reported by Han et al. and Hosseini et al.,^{17, 18} with some modifications. Briefly, the aerogel was immersed in a buffer solution. At predetermined time intervals, 2 mL of the solution was removed and replenished with an equal volume of fresh buffer. The absorbance of the solution at 277 nm was measured using a UV–visible spectrophotometer. The amount of OEO released was expressed as cumulative release percentage.

Antioxidant properties

The antioxidant activity of the aerogels was evaluation using the DPPH assay. ¹⁶ An appropriate amount of DPPH was weighed and dissolved in anhydrous ethanol to prepare a 0.5 mmol L⁻¹ DPPH solution. The samples were mixed with 10 mL of the DPPH solution and reacted in a shaker at 37 °C in the dark for 3 h. The absorbance was determined at 517 nm using a UV–visible spectrophotometer, where A ₀ was the absorbance of the blank control solution and A _i was the absorbance of each sample solution. The antioxidant capacity was calculated using the following formula:

$$\begin{array}{c}\text{DPPH radical scavenging}\left(\%\right)=\left(A_0-A_i\right)/A_0\times 100\end{array}$$ (3)

Antibacterial properties

Antibacterial activity was evaluated by the bacteriostatic circle method. Bacteria were activated by incubating at 37 °C for 12 h. Subsequently, the bacterial suspensions were diluted 1000‐fold using sterile water. Nutrient agar was added to 200 μL of the diluted bacterial solution and spread evenly. The aerogels were placed on Petri dishes, inverted, and incubated at 37 °C for 24 h. The diameters of the inhibition zones were measured after incubation.

Application of aerogels in beef meat preservation

The beef preservation experiment was conducted over 8 days. During this period, the meat was placed on the aerogel and stored in a plastic container at 4 °C. The blank group was packed without padding. Meat samples were removed on days 0, 1, 3, 5, and 7, respectively, to evaluate changes in pH value, total viable count (TVC), total volatile basic nitrogen (TVB‐N), thiobarbituric acid‐reactive substances (TBARS), weight loss, and color.

pH measurement

The pH value of the beef samples was determined according to the method of Wu et al., ¹⁹ with slight modifications. Minced beef (2 g) was homogenized in 18 mL of sterile water. The pH of the supernatant was determined with a pH meter, and each sample was assessed in triplicate.

Weight loss

The initial weight of the beef was recorded as W ₀. The beef was then weighed on days 1, 3, 5, and 7, with the weights denoted as W _t . The weight loss was evaluated according to the formula below:

$$\begin{array}{c}\text{Weight loss}\left(\%\right)=\left(W_0-W_t\right)/W_0\times 100\end{array}$$ (4)

Total viable counts

The TVC of beef was ascertained in accordance with the Chinese National Food Safety Standard Method (GB4789.2–2022). Briefly, 2 g of minced beef was taken on days 0, 1, 3, 5, and 7, and immersed in 18 mL of sterile water for 30 min. Then, 1 mL of the diluted liquid was added to 20 mL of plate count agar, and incubated at 37 °C for 48 h. The results were expressed as log CFU g⁻¹ of meat.

Total volatile base nitrogen

The TVB‐N content in beef was evaluated following Zhou et al. ²⁰ 10 g of minced beef was mixed with 100 mL of distilled water and homogenized for 30 min. The beef suspension was then filtered to remove residues. Prior to distillation, 10 mL of the filtrate was mixed with 5 mL of MgO (20 g L⁻¹). The TVB‐N content was calculated by titrating the distillate with 0.01 mol L⁻¹ HCl, using distilled water as a blank control.

Thiobarbituric acid‐reactive substances

The extent of lipid oxidation in beef was determined following the method by Xia et al. ²¹ Briefly, 2 g of minced beef sample was homogenized with 3 mL of 1% thiobarbituric acid (TBA) solution, followed by the addition of 17 mL of 2.5% trichloroacetic acid. The combined mixture was subjected to boiling water bath heating for 30 min and subsequently allowed to cool to ambient temperature. A volume of 1.5 mL of the sample solution was combined with an equivalent volume of chloroform, subjected to vortex mixing, and then subjected to centrifugation at 3000 × g for 10 min at room temperature. The absorbance of the resulting supernatant was determined at 532 nm. The calculation formula is as follows:

$$\begin{array}{c}\text{TBARS}\left(\mathrm{mg}{\mathrm{kg}}^{-1}\right)=\left(\frac{A_{532}}{m_{\text{sample}}}\right)\times 9.48\end{array}$$ (5)

where A ₅₃₂ corresponds to the measured absorbance of the sample solution, and the m _sample denote the beef sample weight (g).

Color properties

Color changes in beef over different days were assessed using a colorimeter (2060 TS, Aokema, Shandong, China), which measured L* (lightness), a* (redness), and b* (yellowness) values. The appearance changes of beef were recorded with a camera.

Statistical analysis

The data were presented as mean ± standard deviation (SD). Statistical analysis was performed via SPSS 20 (IBM, USA). Analysis of variance was conducted to analyze the data, with Duncan's multiple range test used to assess significant differences (P < 0.05).

RESULTS AND DISCUSSION

Physical and chemical properties of the aerogels

Microstructure of aerogels

From a macroscopic perspective, all aerogels exhibited a complete structural appearance (Fig. 2(A)). SEM analysis of the internal structure of the different aerogels (Fig. 2(B)) revealed that different proportions of oregano essential oil combined with CMC and SA led to the formation of distinct pore structures. It has been reported that the characteristics of aerogels, particularly pore size diameter, could be affected by several parameters, including the type and concentration of polymer, aging time, gelation procedure, and freezing temperature. ²² As shown in Fig. 2(B), the C/A‐0 aerogel displayed a lamellar structure without distinct pores. This phenomenon is primarily attributed to the abundance of hydroxyl groups in CMC, which can form hydrogen bonds with SA molecules. ¹⁵ With the increasing concentration of oregano essential oil, the aerogels developed loose and uneven pores. This may be due to the hydroxyl groups in OEO, which can form intermolecular hydrogen bonds with CMC and SA. As shown in Fig. 2(C), the pore size of the C/A‐0 aerogel was 175.46 ± 45.14 μm, which is significantly smaller than the pore size of the OEO aerogels (218.58 ± 45.52, 245.96 ± 48.45, and 325.96 ± 43.07 μm). This difference is mainly ascribed to the influence of intermolecular hydrogen bonding. Meanwhile, except for the C/A‐0 aerogel, the porosity of all other aerogels exceeded 80%. In the C/A‐2%, 4% and 8% aerogels, the increased hydrogen bonding resulted in a more uniform and ordered pore distribution, which enhanced the adsorption capacity and compressive strength of the aerogel for food active packaging with integrated preservation and buffering functions.

Figure 2.

Structural characteristics of the preservation aerogels: (A) macromorphology of aerogels; (B) SEM images of aerogels (scale bar: 1.00 mm); (C,D) pore size and percentage porosity of aerogels. All data are presented as mean ± SD (n = 3).

FTIR spectrum analysis

FTIR was used to analyze the interactions between CMC, SA, and OEO (Fig. 3(A)). All aerogels displayed a distinctive peak of the amide A band at 3334 cm⁻¹, which relates to the stretching vibration of the —OH group. This observation aligns with the prevalence of hydroxyl groups in CMC, SA, and OEO. The absorption peak at 2921 cm⁻¹ was associated with the amide B band, which originated from the stretching vibrations of O—H and C—H groups within the aerogel structure. ²³ With the addition of OEO, the intensity of this peak becomes stronger, indicating that the presence of OEO promotes the formation of intermolecular hydrogen bonds. The peaks at 1592 and 1260 cm⁻¹ belonged to the C=O stretching vibration and with C—N stretching and N—H bending vibration, respectively. ¹⁶ Importantly, the introduction of OEO led to the emergence of a new weak peak at 1739 cm⁻¹, which may be linked to the asymmetric stretching vibration of C=O resulting from carboxylate groups formed during the emulsification process of OEO. ²⁴ In the FTIR results, the C/A‐0 aerogel and C/A‐2–8% aerogels exhibited similar characteristic peaks, and a new weak peak related to OEO appeared at 1739 cm⁻¹, indicating that OEO was successfully immobilized within the aerogels.

Figure 3.

Physicochemical properties of the preservation aerogels: (A) FTIR spectra, (B) DSC thermograms, (C) water absorption capacity, and (D) compression stress–strain curves of the preservation aerogels. All data are presented as mean ± SD. Different lowercase letters represent significance (P < 0.05).

Thermal stability analysis

Thermal stabilities of the aerogels were investigated using DSC. The DSC curves of aerogels with varying OEO concentrations are presented in Fig. 3(B). The endothermic peaks observed between 100 and 130 °C is regarded as the glass transition temperature (T _g).^{25, 26} The C/A‐0 aerogel exhibited a T _g of 115.75 °C, whereas incorporating OEO elevated the T _g of the C/A aerogel to 128.21 °C. This enhancement of thermal stability might be due to the increased molecular interactions between OEO and the CMC/SA polymers, thereby improving the thermal stability of the aerogels containing OEO.

Water absorption ratio

Aerogels can absorb exudates from meat, making a high water absorption capacity crucial for meat preservation. ²⁷ The water absorption ratio of the C/A‐0, C/A‐2%, C/A‐4%, and C/A‐8% aerogels are shown in Fig. 3(C). The C/A‐0 aerogel exhibited a water absorption ratio of 276%, indicating favorable water absorption ability, which was attributed to the hydrophilicity of the material. Furthermore, the presence of OEO significantly enhanced the water absorption capacity of the aerogels, with C/A‐2% and C/A‐4% aerogels reaching 609% and 532%, respectively. This might be related to the higher porosity of the internal pores of the aerogels (Fig. 2(D)), suggesting that OEO composite aerogels have a favorable structural basis for meat preservation.

Mechanical properties analysis

The structural stability of aerogels serves as an essential structural basis for maintaining their functionality and plays a significant role throughout the preservation process. Figure 3(D) shows the stress–strain curves of aerogels during compression testing. The addition of OEO enhanced the mechanical strain of the aerogels, indicating their high mechanical strength and ability to resist deformation under pressure, which positively impacts the absorption of meat exudate by the aerogels. ²⁸ Therefore, the above results indicated that the OEO composite aerogels exhibited a uniform microstructure, high porosity, enhanced thermal stability and high mechanical properties, which were conducive to the subsequent beef preservation experiments.

Cumulative release rates of OEO‐loaded aerogels

The cumulative release of OEO is shown in Fig. 4. As time progressed, the aerogel rapidly absorbed water and swelled, leading to an increase in the release percentage. Furthermore, with extended incubation time, the essential oil release rate in each sample showed a trend of gradual change. Moreover, the cumulative release percentage increased with increasing OEO concentration. However, as time elapsed, the water‐binding sites of the aerogel became saturated, resulting in a decreased release rate. The porous structure of the aerogel enabled sustained release of OEO, ensuring antimicrobial efficacy without concerns regarding nanoparticle migration and potential cytotoxicity, indicating its potential application in the development of antimicrobial aerogels for food packaging. ²⁹

Figure 4.

Cumulative release rates of oregano essential oil‐loaded aerogels.

Antioxidant properties

Aerogels with antioxidant properties can delay lipid oxidation, thereby extending the shelf life of beef. The antioxidant capacity of the aerogels was evaluated by analyzing their ability to scavenge DPPH radicals. As shown in Fig. 5(A), the C/A‐0 aerogel exhibited a relatively low DPPH radical scavenging rate, which showed an increasing trend with the addition of OEO. Compared with the C/A‐0 aerogel, the radical scavenging rates of the C/A‐4% and C/A‐8% aerogels were significantly enhanced and remained above 72%. This excellent radical scavenging capacity may be attributed to the antioxidant substances of aromatic phenols and terpenoids in oregano essential oil. ¹⁶ Therefore, these composite aerogels show great potential in preventing meat oxidation and extending the shelf life of meat products, making them promising for applications in the preservation of meat products.

Figure 5.

Antioxidant properties and antibacterial activity of different aerogels: (A) DPPH scavenging rate of the aerogels; (B,C) antibacterial properties of the aerogels to Escherichia coli and Staphylococcus aureus, respectively. Different lowercase letters represent significance (P < 0.05).

Antibacterial property

To investigate the antibacterial effects of different amounts of OEO after composite aerogels, Staphylococcus aureus and Escherichia coli were used as test bacteria, and the antibacterial activity of OEO was evaluated measuring the inhibition zone method. According to Fig. 5(B), the aerogels exhibited favorable antibacterial activity. Quantitative results showed that the inhibition zone diameters against E. coli did not exhibit an increasing trend with the OEO content (Fig. 5(C)). However, the inhibition zone diameters against S. aureus increased from 2.55 to 2.8 cm, 3.0 cm, and 3.5 cm, respectively. This enhancement in antibacterial activity may be attributed to the presence of carvacrol or other phenolic compounds in oregano essential oil, which can increase membrane permeability and disrupt the integrity of the bacterial cell membrane, thereby exerting antibacterial effects.^{30, 31} The above results indicated that the aerogels based on OEO hold significant research value in the field of meat preservation.

Meat preservation

Weight loss

Figure 6(A) shows the appearance of beef from different treatment groups during storage. It can be seen that all the beef samples were fresh on day 0 and, on day 7, there were changes in appearance color to varying degrees. Figure 6(B) showed that the weight loss increased in all groups during storage, which was related to protein degradation. The breakdown of key structural proteins can disrupt the myofibrillar structure, leading to a reduction in the water‐holding capacity of the meat. ²⁰ Among them, weight loss in the C/A‐0 and C/A‐4% groups was higher than in the blank group. This could be attributed to the aerogel capacity to absorb meat exudate, thereby inhibiting extensive microbial proliferation. This is consistent with the observations of Behnaz et al., ³² and the growth of microorganisms is the main factor affecting the water‐holding capacity of muscle fibroblasts during storage.

Figure 6.

Color and appearance changes of beef during storage. Changes in (A) appearance, (B) weight loss, (C) L*, (D) a*, and (E) b* values of blank and different aerogel treated beef samples under storage.

Color analysis

As shown in Fig. 6(C)–(E), the color of the meat is one of the key indicators for evaluating freshness. In this study, the changes in beef color and their relationship with the preservation effect were thoroughly investigated by measuring the L*, a*, and b* values of beef during the preservation process. The L* value reflects the lightness of the surface of the beef. With the extension of storage time, the L* value gradually decreases, mainly due to the denaturation of myoglobin on the beef surface during the oxidation process, which leads to a weakened ability to reflect light. ⁷ In addition, the growth and metabolism of microorganisms may produce pigment substances, further reducing the brightness of the beef surface. As presented in Fig. 6(C), with the lengthening of storage duration, the L* values of all meat specimens exhibited a declining pattern. Among them, the L* value of the blank group was the lowest at 7 days, while the L* values of the C/A‐4% and C/A‐8% groups decreased more slowly, indicating that the aerogel played a role in preservation. The a* value is a key indicator for measuring the redness of beef. The a* value of fresh beef is usually high. During the preservation process, the trend of a* value change is similar to that of the L* value, but the amplitude of change is more significant. This is because myoglobin is oxidized from oxymyoglobin (red) to metmyoglobin (brown) during the oxidation process, resulting in a rapid decrease in a* value. As depicted in Fig. 6(D), the a* values of all meat samples demonstrated an initial increase, followed by a decrease. This trend might be explained by the interaction between oxygen and myoglobin in fresh meat, which facilitates the formation of oxymyoglobin and consequently results in meat reddening. ³³ As storage time extended, the a* value of the blank group rapidly decreased and dropped to 5.68 on the 6th day. The red color of the beef gradually faded, eventually presenting a brown or gray‐brown appearance (Fig. 6(A)), indicating that the beef had undergone obvious oxidative spoilage. In contrast, the a* values of the other treated groups decreased to 7.11, 6.93, 7.17, and 7.89 – all higher than the 5.68 of the blank group. This phenomenon suggested that aerogel treatment contributes to preserve the red color of the meat. The b* value reflects the degree of yellowness, and a higher b* value exhibited more bacterial contamination. ³⁴ As shown in Fig. 6(E), the b* values of each group exhibited an upward trend with prolonged storage. On day 7, the b* value of the blank group reached the highest level, followed by the C/A‐0 group, while the C/A‐2% and C/A‐8% groups had the lowest b* values. This yellowing effect was due to lipid oxidation. ³⁵ The above results suggested that the aerogel contributes to beef preservation, and this effect was proportional to the increase in OEO.

pH value

The pH value is an important indicator for measuring the acidity or alkalinity of beef, which is closely related to the quality, freshness, and microbial growth environment of beef. Figure 7(A) shows that the pH value of beef samples increased with time. In the early stage, the pH value of beef remains relatively stable, indicating that the muscle tissue of fresh beef is in a normal metabolic state, and its internal enzymatic system and acid–base buffering system can maintain the balance of pH value. ³⁶ As storage time increased, the pH value of the blank group increased significantly. On day 7, the blank group exhibited severe spoilage, and its pH value surpassed 6.6. This might be due to bacterial and enzymatic decomposition of proteins into alkaline ammonia and amine molecules. ³⁷ The pH value of the aerogel‐treated groups increased slowly, especially with OEO, which remained below 5.6. This might be because their water absorption and the antimicrobial effect of OEO helped delay bacterial proliferation.

Figure 7.

Effect of different aerogels on (A) pH, (B) TVB‐N, (C) total viable counts, and (D) TBARS of beef during storage. Different lowercase letters indicate significant differences at the same storage times (P < 0.05).

Total volatile basic nitrogen

The content of TVB‐N mainly originates from the decomposition of proteins in beef during storage. When microbial activity in beef intensifies or its own enzyme system functions, proteins will gradually decompose to produce volatile alkaline nitrogen‐containing substances, referred to as TVB‐N.^{38, 39} The China National Standard System (GB2707‐2016) stipulates that the limit of the TVB‐N value for fresh beef is 15 mg/100 g and it is not recommended for consumption when the TVB‐N value exceeds 15 mg 100 g⁻¹. ³⁵ As depicted in Fig. 7(B), the TVB‐N values of all treatment groups were below 15 mg 100 g⁻¹ in the first 5 days, but showed a trend of increasing with time. After 7 days, the TVB‐N values of the blank group and the C/A‐0 group were 22.08 and 15.48 mg 100 g⁻¹, respectively. However, the TVB‐N values of the C/A‐2%, C/A‐4%, and C/A‐8% groups were 10.04, 9.92, and 9.80 mg 100 g⁻¹, respectively, which did not exceed the standard. This indicates that the aerogel groups containing OEO could inhibit microbial growth and reproduction to some extent, reducing the accumulation of biogenic amines and ammonia produced by microbial and endogenous enzyme activities in meat protein degradation, and thereby extending the preservation time of meat. The antibacterial effect of essential oils caused TVBN to be lower than that the untreated samples, which was consistent with previous study results. ⁴⁰

Total viable count

TVC is a key indicator for measuring the degree of microbial contamination and the effectiveness of preservation in beef. The TVC values were significant for assessing the quality changes of beef during storage. A TVC value that surpasses 6 log₁₀ CFU g⁻¹ signifies that the meat has spoiled. ⁴¹ As depicted in Fig. 7(C), there was an increase in the TVC values of all groups with the extension of storage time. The TVC of the blank group reached 6.92 on day 7, indicating that the beef had spoiled. The TVC values of the C/A‐0 and C/A‐2% groups were 5.68 and 5.036, respectively, demonstrating that the beef was close to spoilage. In contrast, the TVC values of the C/A‐4% and C/A‐8% groups were only 4.42 and 4.37, respectively. The above findings suggest that the porous structure of the aerogel absorbed a large amount of exudate, thereby preventing the rapid growth of microorganisms. The excellent TVC control effect exhibited by the C/A‐4% and C/A‐8% groups may be due to the outstanding antibacterial ability of OEO, which further inhibits microbial growth. ⁴² The results of TVC values aligned broadly with those of pH values.

TBARS value

During the storage of beef, lipid oxidation is an inevitable chemical reaction process. It leads to a decline in the flavor, color, and nutritional value of beef, while generating harmful oxidation products that affect the quality and safety of beef. The TBARS value is commonly used to assess the degree of lipid oxidation in beef; a higher TBARS value indicates a greater extent of lipid oxidation. ⁴³ During the storage period, the blank group had the fastest growth rate in TBARS value, increasing from 1.33 to 5.78 mg malondialdehyde (MDA) kg⁻¹ (Fig. 7(D)). This occurred because the sample was subjected to direct exposure in the packaging tray and underwent lipid oxidation. The ROS generated from lipid oxidation would further expedite the oxidation process. ⁴⁴ Conversely, the growth rates of TBARS values in the C/A‐2%, C/A‐4% and C/A‐8% groups were relatively slow, at 3.39, 3.09, and 3.02 mg MDA kg⁻¹, respectively, after 7 days. This indicates that aerogels with higher OEO concentrations were superior in delaying lipid oxidation in beef, which aligned with the TVC results. In summary, the porous structure of the aerogel effectively absorbed excess exudate from beef, preventing exudate accumulation and subsequent microbial proliferation. Importantly, the bioactive compounds in OEO might inhibit bacterial growth by disrupting membrane integrity, leading to leakage of intracellular contents (Fig. 8(A)). ⁴⁵ Additionally, intracellular ROS could further damage bacterial membranes via oxidation of the phospholipid bilayer.^{46, 47} These synergistic mechanisms significantly enhanced beef preservation.

Figure 8.

Correlation analysis of various indicators during the storage of beef, and schematic diagram of the antibacterial mechanism: (A) antibacterial properties of the aerogels; (B,C) correlation analysis and principal component analysis of freshness discrimination.

Correlation analysis

Based on the correlation coefficients among TBARS, TVB‐N, pH, TVC, L*, a*, and b* indicators, the coordinated changes of different indicators during the storage of beef were evaluated. As shown in Fig. 8(B), TBARS, TVB‐N, pH, and TVC exhibited significant positive correlations. As the storage time increased, microbial proliferation on beef surfaces intensified (increased TVC), and their metabolic activities accelerated protein decomposition, resulting in an increase in TVB‐N content and pH value. Meanwhile, the microbial metabolism also promoted lipid oxidation, generating lipid oxidation products such as MDA, leading to an increase in TBARS content. Moreover, the increase in TBARS content may cause the color of the beef to darken, reflecting the degree of oxidation on the surface of the beef. The increase in TVC further introduced microbial metabolites on the beef surface, which negatively impacted its visual appearance.

To further assess beef freshness, principal component analysis (PCA) was performed on the basis of TBARS, TVB‐N, pH, TVC, and color parameters. As shown in Fig. 8(C), the cumulative contribution rate of PC1 and PC2 reached 83.8%, reflecting most of the information of the samples. Throughout the 7‐day storage period, the freshness of the beef can be roughly divided into three stages of ‘fresh’ (0 d), ‘start to spoil’ (1–3 d), and ‘completely spoiled’ (5–7 d). These stages basically reflect the quality change pattern of the beef.

CONCLUSIONS

In this research, a novel OEO‐loaded composite aerogel was successfully prepared based on an alginate/CMC. Distinct from conventional single‐component counterparts, the resulting aerogel not only achieved enhanced mechanical properties but also integrated remarkable antibacterial and antioxidant potentials in a synergistic manner. Notably, comparative tests indicated that, compared to the blank group and the OEO‐free C/A‐0 aerogel group, the C/A‐4% and C/A‐8% OEO‐loaded aerogels markedly decreased the TVC, TVB‐N, pH and TBARS values of chilled beef. This effectively preserved the beef's color stability and considerably extended its shelf life. Mechanistically, the porous alginate/CMC matrix efficiently absorbs beef exudate to eliminate the moist microenvironment conducive to bacterial growth, while the sustained‐released OEO disrupts microbial cell membranes and scavenges ROS, integrating physical exudate absorption with bioactive release. These results demonstrate that the alginate/CMC–OEO aerogel system innovatively realizes the synergistic integration of exudate absorption and active antibacterial/antioxidant release, overcoming the limitations of traditional single‐function preservatives. This unique dual functionality, together with the sustainable and biodegradable matrix properties, positions it as a promising eco‐friendly packaging material for significantly enhancing meat preservation quality.

FUNDING INFORMATION

This work was supported by the Liaoning Provincial Natural Science Foundation – Doctoral Research Start‐up Fund Project (2025‐BS‐0853, YW) – the College Students’ Innovation Training Program of Liaodong University (S202511779003, XL), and the Doctoral Research Startup Foundation of Liaodong University (XJ2025003502, YW).

CONFLICT OF INTEREST

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

AUTHOR CONTRIBUTIONS

XL: formal analysis; methodology; writing – original draft. DW: methodology; visualization; formal analysis. RL: conceptualization; methodology. ML: data curation; formal analysis; supervision. XM: validation; visualization. YW: data curation; funding acquisition; project administration; supervision; writing – review and editing.

DATA AVAILABILITY STATEMENT

No datasets were generated or analysed during the current study.