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Functional Composite Materials
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Nano-modifications of edible materials using ionizing radiation for potential application in active food safety

Functional Composite Materials volume 5, Article number: 8 (2024) Cite this article

Abstract

Active food packaging films from Carboxy methyl cellulose and starch (CMC-g-Starch) reinforced with Magnesium-oxide (MgO) NPs are created and characterized. The effect of different particle sizes, MgO NPs concentrations and different gamma irradiation doses on the preparation of (CMC-g-Starch-MgO) edible nanocomposite films were investigated to determine their properties. Several analytical methods, such as swelling behavior, FT-IR, TEM, TGA, and mechanical characteristics, are represented to investigate different characteristics of the prepared (CMC-g-Starch-MgO) edible nanocomposite films. Also, the prepared (CMC-g-Starch-MgO) edible nanocomposite films and their coating were subjected to the fresh Peaches fruits. Their effect on the Peach fruits' lifespan was evaluated. The anti-microbial property of the edible (CMC-g-Starch-MgO) nanocomposite films of gram (+ve) and gram (–ve) bacteria was reported. Results represented the thermal and mechanical characteristics of (CMC-g-Starch-MgO) edible nanocomposite films, which were enhanced by γ irradiation. Also, the irradiated (CMC-g-Starch-MgO) edible nanocomposite films and their coating extend the lifespan of Peaches fruits and exhibit resistance to pathogenic microorganisms. In conclusion, (CMC-g-Starch-MgO) edible nanocomposite films fulfilled the required behaviors for the application in the nanofood packaging era.

Introduction

A common way to prevent food from spoiling and increase lifespan is edible surface coating. Moisture and oxygen could be prevented and isolated from passing through by using a thin coating to lower respiration rates, reduce water loss, and keep food fresh for an extended time. Because synthetic materials negatively influence the environment, recent food packaging trends are moving away from traditional plastic and paper packaging materials and towards natural and ecologically friendly biodegradable packaging films [21].

Polymers, including polysaccharides, cellulose derivatives, or pectin, could be used to prepare edible nanocomposite films. Since they have high carbon dioxide and oxygen barriers and are colourless and tasteless, polysaccharides are commonly utilized in nanofood packaging [18].

Due to its inexpensive price, wide availability, and renewable natural polysaccharide, starch has drawn a lot of attention in edible food packaging. Starch is entirely biodegradable and decomposes into environmentally benign compounds like carbon dioxide and water [42]. Starch films prepared by casting, these nanocomposite films have significant drawbacks, such as worse mechanical and moisture resistance. As a result, several researches have been done on starch adjustments, as combined with other polymeric materials, to enhance the starch membranes' mechanical and thermal characteristics [27].

Natural cellulose is the most prevalent kind of polysaccharide. Carboxymethyl cellulose (CMC) is an excellent option for food packaging since it is a hydrophilic compound of cellulose derivative and has robust capabilities of membrane formation, is nontoxic, and is biodegradable. It is also a great choice because it is cheaply priced [44].

The latest research has displayed that metal oxide reinforcement in polymer blend provides superior anti-bacterial and ultraviolet protection characteristics. Extending the lifespan of packaged foods by adding metal oxides, such as ZnO and MgO, into various polymeric materials blends [35]. The reproducible, colourless, crystalline mineral magnesium oxide (MgO), one of several metal oxides, is found in nature and may be inexpensively synthesized in mass production [40].

Additionally, the FDA authority accepts the usage of MgO as a food grade. The researchers previously revealed the anti-bacterial efficiency UV prevention competencies of the developed MgO nanocomposite films [43, 46].

In the current study, the irradiation approach is a hygienic tool employed for copolymerization reaction, leading to a crosslinking process. CMC-Starch edible blends of varying proportions 1:1, 1:2, and 2:1 were developed to create a (CMC-g-Starch-MgO) edible nanocomposite films, and MgO nanoparticles were mixed into a polymeric matrix of CMC and starch.

The blends were constructed, and the swelling behaviour, TEM, FT-IR, mechanical characteristics, and thermal properties of the blends were evaluated. It was calculated how varied MgO concentrations and particle sizes in the prepared solution would affect the characteristics of the produced nanofilms. Also, it was investigated how varying doses of γ-radiation affected the thermo-mechanical behaviors of the (CMC-g-Starch-MgO) edible nanocomposite film. This examine the effectiveness of (CMC-g-Starch-MgO) edible nanocomposite film in enhancing Peaches’ lifespan. Also, the produced (CMC-g-Starch-MgO) edible nanocomposite film anti-bacterial activity was assessed for use in food packaging.

Materials and methods

Carboxy-methyl-cellulose was bought from Egypt's El-Naser CO. El-Gomhouria CO in Egypt offered maize starch that was 27% amylose and 73% amylopectin. El-Gomhouria CO in Egypt supplied the glycerol 99.5% (Mwt, 92.09). Mumbai, India's Lobachemie PVT. LTD. supplied the citric acid.

Irradiation facility

Gamma irradiation was performed using a Canadian Cell irradiator with 60Co as an irradiation source, Atomic Energy Authority-Cairo, Egypt.

MgO nanoparticles preparation

3 gm. of CMC-Starch were liquefied in 100 ml of sterilized water to create a CMC-Starch (1:1) solution. CMC-Starch was used as stabilizing agent. CMC/Starch act as a stabilizing agent and also prevents the agglomeration of nanoparticles. When the polymer solution was fully soluble, the CMC-Starch solution was heated to 80° C and vigorously swirled using a magnetic stirrer for 6 h. Then, 0.1M Mg(NO3)2 was added to the blend solution while it was continuously stirred for around 2 h. It was allowed for the CMC-Starch solution to cool to ambient temperature. To ensure that the solutions were evenly homogeneous, all of the solutions were held with constant stirring for around 3 hours. The CMC/Starch nanocomposite irradiated at 10 kGy of γ-radiation. then, (20 ml) of (0.3 M) sodium hydroxide solution was added in drops along the sides of the container under constant stirring for 2 hours and allowed to settle for 24 hour. Magnesium hydroxide was created .Then centrifuged for 30 minutes at 15,000 rpm. Magnesium hydroxide was then cleaned using organic solvents and de-ionized water (ethanol). Filtered, dried for 12 hours at 110° C in a lab oven, and then calcined for 4 hours at various temperatures, including 500, 600, and 700° C, to produce fine MgO nanoparticles of various particle sizes. The generated MgO nanoparticles were then characterized using a variety of methods. The samples obtained at 500° C had the lowest particle size; thus, they were chosen for additional testing.

Preparation of CMC-Starch mixes

A number of CMC-Starch mixes of varied proportions were created through the casting procedure.

An aqueous solution containing 2 wt% (CMC) was made at 85°C while being stirred till completely dissolved. The starch mix was made by scattering 1.5 weight percent of starch in de-ionized water, heating it to 80 degrees, and stirring continuously until the starch gelatinized utterly.

Combining Carboxy-methyl-cellulose mix with starch at various comonomer-compositions of (1:1, 1:2, and 2:1) CMC-Starch blends were created. Citric acid was added as a cross-linker as 1.5 wt% and 30 wt% plasticizers of glycerol while a mix of both polymers was stirred at 75 OC for two hours till it became a homogeneous mixed solution. By pouring the mixture solutions into Petri dishes and drying them openly by air, films with 0.3 mm thickness and 25 cm diameter will be produced. Due to its ideal swelling percentage, the 1:2 CMC/Starch blend film was chosen for additional testing.

Preparation of (CMC-g-Starch-MgO) edible nanocomposite films

The chosen CMC/Starch mixture was combined with 1% MgO solution, calcined at 500, 600, and 700 OC, and stirred for three hours at 80 OC. The blend was then homogenized by sonication for 30 minutes. As indicated earlier, films were created by pouring the mixtures into the glass Petri dishes.

Preparation of irradiated CMC-Starch-MgO blend

To create homogeneous blends, the created CMC-Starch blend was combined with various concentrations of (MgO 500) nanoparticles (1, 1.5, 2, 2.5, and 3 wt %) and swirled continuously at 80o C for 3 hours. Solutions of the CMC-Starch-MgO were cast in the air at ambient temperature. The nanocomposite films that were obtained have specific characteristics. The optimal blend concentration was chosen for further research based on the findings of these experiments. The chosen (CMC-g-Starch-MgO) edible nanocomposite film was prepared using multiple γ-radiation doses (10, 15, 20, and 30 kGy).

Characterization of (CMC-g-Starch-MgO) edible nanocomposite films

FT-IR spectra analysis

FTIR-Vertex/70-spectrophotometer (Bruker, Karlsruhe, Germany) was chosen to determine the materials' functional groups across the spectrum range of 400–4000 cm1. At Cairo University- Egypt.

Transmission electron microscopy, (TEM)

MgO nanoparticles were analyzed using a TEM instrument (JEOL, JEM100CS, Japan) to determine their size and shape. Samples were prepared for TEM examination by diluting, fixing, and allowing them to dry at room temperature on carbon-coated copper grids.

Swelling studies

At 37 °C, distilled water was used to soak the pre-weighed dry films. Swollen films were removed at predetermined intervals, carefully dried with filter paper, and then weighed with a precise balance. The measurements were carried out until each sample's weight remained consistent. According to the upcoming equation [Eq. (A.1)] to calculate the (S %) swelling ratio:-

$$S \%=\frac{Ws -Wo}{Wo} \times 100$$
(A.1)

Where Ws represents a swelled sample, and Wo represents a dry sample. The swelling test was performed many times, and average values of the data were presented.

Mechanical properties

Mechanical characteristics were measured by the "Instron instrument" (model 1195-England), also including tensile-strength measurements and elongation as well. Five measurements for each run were taken to record the values.

The mechanical properties of nano composite films of tensile strength and elongation (%) at break point were conducted at room temperature via "Instron instrument" (model 1195-England), according to ASTM D 882-02 and crosshead speed 5 mm/min by load cell 100 N. Every value either tensile strength or elongation at break point were measured triplicate as mean value.

Thermogravimetric (TGA) analysis

TGA thermograms, was performed for samples to figure out their thermal properties. Results were obtained using a Shimadzu apparatus in Kyoto, Japan, in the range of (ambient temp-600°worC) at a rate of 10°C/min, and nitrogen was at a rate of 20 ml/min.

Coating application on Peaches

Peaches fruits were purchased from a nearby place, and for this study, only Peaches fruits with consistent size and were free of obvious damages or fungal rot were chosen. The coating solutions were applied to the peaches for 5 minutes, the excess was drained, and the covered Peaches were allowed to air dry. To assess the lifespan, all samples were kept at ambient temperature for 14 days. Peaches that weren't covered served as controls.

Assessment of anti-microbial activity

A Gram(-ve) pathogen (Pseudomonas aeruginosa) and a Gram(+ve) pathogen (Staphylococcus aureus) were both tested for the edible nanocomposite films' anti-bacterial effectiveness. Films were laid out on Petri plates with medium (Pseudomonas aeruginosa culture) and (Staphylococcus aureus culture) and then protected at 38° C for 18 hours.

Results and discussion

FTIR- Spectroscopy

The chemical structure formed from starch, CMC, and MgO was analyzed using FT-IR spectra. Fig. 1 represents the infrared bands and spectra of the neat-starch, neat-CMC, prepared (CMC-Starch), and (CMC-g-Starch-MgO) edible nanocomposite films. The distinctive wide absorption bands discovered at 3319 and 3356 cm-1 suggest stretching vibration bands of OH, hydroxyl of starch, and CMC, separately, and the spectra were broadened, which may be due to H-bonding formation [47, 49]. Peaks in the prepared (CMC-Starch) spectrum shifts due to the intersection between the OH groups of citric acid, starch, glycerol, and CMC. C-H stretching vibration band is attributed to the spectra around 2920 cm-1. C=O (carbonyl) of CMC and starch, respectively, exhibit stretching vibrations at 1714 and 1716 cm-1, whose intensities are attributed to the degree of substitution [33].

Fig. 1
figure 1

suggested reactions mechanisms formation of the (CMC-Starch) film at 85°C and stirred in presence of citric acid and glycerol

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In the CMC-Starch blend, the C=O (carbonyl) signal is shifted to 1723 cm-1, demonstrating that the citric acid-induced crosslinking of polysaccharide derivatives has occurred [14, 20]. The CMC molecule's carboxyl group (COO-) correlates with the peaks seen at 1410 and 1585 cm-1 [7]. In the CMC-Starch spectra, 1410 cm-1 was moved to 1403 cm-1, illustrating the overlapping of starch and CMC through (COO and OH groups) [36, 48]. CH2 and OH groups are responsible for the absorption bands at 1336 and 1210 cm1. The stretching vibration bands in starch and CMC are found at 1010 and 1032 cm-1 of (C-O-C), indicating that more substantial H-bonds developed through starch molecules than between CMC molecules. This could be because CMC has more degrees of substitution, which might be why steric repulsion is more strongly favored. In the CMC-Starch spectra, these peaks were pushed towards inferior wavenumbers at 1008 cm-1, demonstrating the durability of H-bonds established between CMC-Starch [34, 45]. The distinctive spectra of the CMC-Starch blend are comparable to the peaks of neat-starch and neat-CMC, but they have been shifted and widened, suggesting that the CMC-Starch mix has been successfully prepared. FTIR spectrum of (CMC-g-Starch-MgO) edible nanocomposite films was equal to CMC/Starch with just a slight variation in peak spectrum intensity, indicating that the MgO-nanoparticles introduced have not significantly changed the blend structure. The production of the produced matrix is confirmed by the typical peak of (CMC-g-Starch-MgO) edible nanocomposite films at 607 cm-1 [1], which is connected to Mg-O-Mg tensile vibration. The vibration of Mg-O and Mg-O-Mg is what causes a peak at 857 cm-1 [5]. OH broadening vibration of the water molecules at 3296 cm-1 in the matrix of the MgO nanoparticles. As the stretching vibration is conjugated, a peak appears at 776 cm-1 [9].

Transmission electron microscope (TEM) imaging

Using TEM, it was determined how different radiation dosages affected the shape and size of MgO-nanoparticles. As shown in Fig. 2, the pictures proved that the MgO particle sizes are uniform distribution and of uniform spherical shape at the nanoscale. MgO-nanoparticles when heated to 700 °C, the resulting particles alternated in sizes from 31 to 60 nm, with a size of 43 nm (Fig. 2a). The mean size of 16 nm when MgO is heated to 600 °C where the produced particles be likely to be minor in the 12–17 nm. (Fig. 2b).

Fig. 2
figure 2

suggested reactions mechanisms formation of the (CMC-g-Starch-MgO) edible nanocomposite film under effect of gamma irradiation of 60Co as a main source in presence of Magnesium oxide-nanoparticles

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At 500 °C, the size of the particles continued to decrease, and it is estimated that their diameters vary from 8 to 17 nm (Fig. 2c). MgO-nanoparticles produced at 500 °C appeared to have the lowest mean diameter. It is obvious that the average particle size steadily decreased when calcination was reduced. It might be attributed to a decrease in particle size brought on by the intramolecular crosslinked structure improved with radiation-induced polymerization [29]. The electric charge on the surfaces of the nanoparticles may have caused a little particle aggregation that might contribute to the attractive electrostatic attraction between them [4].

Swelling studies

Figure 3a shows the well-defined swelling properties of CMC-Starch mixes with various comonomer-compositions of 2:1, 1:1, and 1:2 against the time factor. Results showed the absorption capability of CMC-Starch compositions arranged in the following order: 2:1 > 1:1 > 1:2. The presence of more free hydrophilic character due to hydrophilic sites in CMC causing an extra water absorption which was demonstrated for CMC-Starch mix with a composition ratio of 2:1.

Fig. 3
figure 3

FTIR spectra of neat-starch, neat-carboxymethyl-cellulose (CMC), CMC-Starch blend without gamma irradiation as well as the irradiated (CMC-g-Starch/MgO) edible nanocomposite film

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The hydrogen bonding link in CMC-Starch might create a robust framework with an amorphous area that could hold water [50]. As shown in the composition of CMC-Starch, the ratio was (2:1), and it was discovered that the swelling behaviour decreased as the CMC content was reduced. This finding might be clarified by the different crosslinking reaction and hydrogen-bonding link of overlapping of starch and CMC through (COO and OH groups), which would reduce the hydrophilicity of the blend by reducing their hydrophilic functional groups in the interactions. This was in line with the findings of several researchers who provided similar information [53].

As shown in Fig. 3a in the 1:2 CMC-Starch film, the swelling behaviour decreased more as the starch level in the feed solution continued to rise. Due to the Starch crystallinity of will limits the pores' sizes and voids to hold water, which may be the main reason for that [14]. It is generally known that the hydrogen bonding and crystalline structure of mixed films have a significant role in how swellable they are [14, 53]. Lastly, a 1:2 CMC-Starch mix was chosen for its more extraordinary water-resistant characteristics, which are necessary for packing.

Figure 3b also depicts the impact of irradiation dosage on the equilibrium swelling of a 1:2 CMC-Starch film. It is clear that according to γ-radiation doses increments from 5, 10, 15, 20, and 30 kGy, the ability to absorb water decreased because the gamma irradiation led to the development of an extra crosslinked polymer configuration matrix that prevented the penetration of water into polymeric chain-matrix. This was due to a higher water uptake because gamma irradiation degradation will occur at high γ-radiation doses, 15, 20 kGy [3].

Mechanical properties

Mechanical characteristics are an essential variable influencing the properties of food packaging ingredients, and their mechanical performance is suitable for applied usage [39]. Starch, in particular, has weak mechanical characteristics. Hence several works have been undertaken to enhance these capabilities, including introducing nanofillers as MgO-nanoparticles [28]. Tensile strength is the highest allowed straining force that a tested sample can bear while being overextended with no rupturing happening, and an elongation test at the breakdown, which is a degree of the sample ductility, is used to define mechanical qualities.

A variety of structural elements influences the mechanical characteristics of ingredients. These considerations include the material's crystallinity, plasticization property, crosslinking affinity, chemical structure, and copolymerization process. The degree of matching with amylose, which results in improved mechanical characteristics, glycerol is frequently utilized as a crosslinking plasticizer agent in the creation of films from starch [6]. Citric acid has been claimed to have the ability to crosslink starch-CMC film, increasing both its tensile strength and elasticity [12].

The chosen (CMC-g-Starch-MgO) edible nanocomposite film, with a composition ratio of 1:2:1.5%, was tested in the current work to determine how the particle size of MgO that was subjected to various calcination (500, 600, and 700 °C) conditions affected the mechanical characteristics of the material. According to Fig. 4a, 500 °C had the lowest percentage of elongation and the maximum degree of tensile strength. The increased surface area of the MgO-nanoparticles in the mix may have reinforced their presence by enhancing their dispersion in the co-polymer blend and strengthening their crosslinking with the CMC-Starch as represented in Fig. 6 [2].

Fig. 4
figure 4

TEM imaging of nanoparticles of MgO at different calcination, (a) 500 °C, (b) 600 °C, and (c) 700 °C

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The capacity of the material to create potent molecular bonds determines how the tensile strength values change. Although MgO nanoparticles with larger particle sizes calcined at 600 and 700 °C showed decreased tensile character. Findings might be explained due to a heterogeneous dispersal of MgO-nanoparticles in the polymer blend. The results show that a CMC-Starch-MgO nanocomposite film calcined at 500 °C was chosen for additional testing since it had the best mechanical characteristics. So, it is reasonable to assume that adding MgO-nanoparticles to the mixed film enhanced its mechanical properties.

Additional research was done on the impact of adding various MgO concentrations (1, 1.5, 2, 2.5, and 3 wt %) on the mechanical characteristic of the CMC-Starch-MgO matrix, and results are demonstrated in Fig. 4b. Tensile values were observed to rise at MgO-nanoparticle levels of 2.5 wt%, and then they are disposed to fall at more significant values. This increase in tensile-strength values with the raising of MgO concentration is due to the blend's components' increased compatibility and propensity to form strong molecular bonds, increasing the nanofilm tensile strength. Moreover, the additional hydrophilic groups offer more opportunities for interactions.

According to reports, a film's mechanical characteristics are significantly influenced by the compatibility of its constituent parts [32]. Many stronger chemical bonds between molecules are generated as the affinity between the ingredients rises, improving the film's strength [19]. As the MgO concentration was raised to 2.5 wt%, the elongation degree at break was reduced. This is due to the MgO-nanoparticles in the mix, which caused the elongation percentage to decrease. In fact, the amount of crosslinking inside the polymer matrix that restricts the polymer's free motion versus the used force plays a role in the change in the film's elongation [2]. While at more significant MgO levels, the tensile strength decreased, probably due to inadequate bonding at the interface. It was interesting to see that MgO-nanoparticles could change the characteristics of the prepared CMC-Starch matrix in the current research. The impact of various γ-radiation doses (5, 10, 15, 20, and 30 kGy) on the characteristics of the chosen (CMC-g-Starch-MgO) edible nanocomposite film (1:2:2.5 wt %) was also investigated and depicted in Fig. 4c. The tensile strength of the CMC-Starch-MgO mix steadily rose with an accompanying reduction in elongation % when the irradiation dosage was raised, indicating that gamma irradiation had a significant impact on the blend's mechanical behaviour [17]. Production of free radicals forms an interaction within the CMC-Starch blend or binds with MgO via an H-bond may be responsible for this improvement in mechanical properties caused by radiation [23]. This network may limit the free movement of the molecular chains [52]. Furthermore, the greater the irradiation doses, the tensile strength declined, and the elongation % enhanced. This may be related to the start of fractures and the degrading process of irradiation.

Thermogravimetric analysis (TGA)

Food packaging films may be subjected to extra temperature during production or applications. The thermal properties of the manufactured nanocomposite films is a crucial characteristic to consider for their appropriateness for usage in the food packaging business [22]. TGA is a tried-and-true method for calculating the thermal steadiness of manufactured nanofilms across a range of temperatures. The degradation ratio against ranges of different temperatures degrees was given in Table A.1 along with the TGA thermograms charts of CMC-Starch film and (CMC-g-Starch-MgO) edible nanocomposite films irradiated at 10 and 20 kGy in a range of temperature between 100 °C to 600 °C.

Table 1 The Degradation percentage of the prepared (CMC-Starch) and (CMC-g-Starch-MgO) edible nanocomposite film gamma irradiated at 10 and 20 kGy at various temperature degrees
Full size table

When compared to the prepared (CMC-Starch) film, the gamma-irradiated (CMC-g-Starch-MgO) edible nanocomposite film showed less weight loss, indicating that MgO has a substantial influence on the Thermo-behaviors of the prepared film.

This increase in hydrogen-bonding availability contact between the MgO and CMC-Starch polymer blend, which together create a strongly crosslinked structure, may be responsible for this improvement in heat stability [25, 26]. According to reports, heat stability is one method for assessing the miscibility of polymeric blends [11]. The shielding blockade influence of nanomaterials on the superficial layer, which inhibits water loss and weight loss process volatilization from the prepared film and subsequently postpones the film deterioration, can be used to explain why (CMC-g-Starch-MgO) edible nanocomposite films lose less weight than other films [51].

There were four key steps to the heat degradation of the CMC-Starch mix film's weight damage. The first step began at ambient and continued up to 100°C with weight damage of 2.5% [31]. The weight loss of 10.6% during the second step, which took place between 160 and 200 °C, may have been caused by the volatilization of the plasticizer glycerol [15]. It is likely that the third stage, which took place between 250 and 400 °C, was caused by the thermal breakdown of the intermolecular crosslinking of neat-starch and neat-CMC, which happens at identical dissociation degrees [16, 38]. The fourth phase, which had a weight loss of 85% and occurred between 450 and 600 °C, was caused by the polymers' C-C backbones fragmenting. The thermograms of TGA of (CMC-g-Starch-MgO) edible nanocomposite film exposed to radiation at 5 and 15 kGy also showed behaviour that was comparable to that of CMC-Starch mix film, showing a similar damage process in four phases with rising heat level Fig. 5. By increasing the radiation dose, it was found that irradiated samples became more thermally stable. This might be attributed to the augmented intra-crosslinking interaction that radiation causes, which in turn reduces mobility and inhibits the chain transfer reaction between the CMC-Starch chain and MgO-nanoparticles in the film. According to these findings, (CMC-g-Starch-MgO) edible nanocomposite films that have received radiation exhibit more thermal-stable than CMC-Starch films.

Fig. 5
figure 5

Swelling behavior of CMC-Starch polymer matrix at (a) different co-polymer compositions and (b) Various irradiation doses of CMC-Starch (2:1) composition

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Anti-bacterial activity

Many researchers have recently studied the prospect of developing inexpensive, effective technologies to combat the detrimental effects of bacteria linked to food packaging membrane surfaces. Places with diverse membrane types attract bacteria, algae, and diatoms [8].

MgO-nanoparticles interact with bacteria more effectively than larger particles due to their properties. As a result, nanoparticles exhibit more pronounced anti-bacterial properties. Current research has revealed that these nanoparticles are selectively harmful to bacteria while having no impact on human cells [37].

MgO demonstrates solid anti-microbial properties. Nano-sized MgO may then interact with the microorganism’s surface and/or with the microorganism's main structure where it goes within the cell wall, consequently displaying unique anti-bacterial processes. Most of the contacts among these unusual nanomaterials and microorganisms are harmful and have been used for anti-microbial applications in biomedical and surgical equipment, cosmetics, synthetic fabrics, and water treatment [41].

MgO has been employed by several scientists as an antibiotic against human pathogenic bacteria and fungi [13, 24]. Researchers found that nano MgO inhibited the growth of many types of bacteria [10].

This work assessed the anti-bacterial property of nano MgO against Staphylococcus aureus and Pseudomonas aeruginosa. Figure 6 represents that MgO-nanoparticles adjusted nanofilms displayed higher anti-bacterial character towards the (+ve) organism S. aureus rather than the (-ve) organism Pseudomonas aeruginosa. The inhibition zone of S. aureus was found to be ranged between (14-27 mm) in all the used concentrations. On the contrary, all samples exhibited anti-microbial character towards (-ve) organism Pseudomonas aeruginosa, and the inhibition zone ranged between (11- 22 mm) except the blank CMC-Starch membrane.

Fig. 6
figure 6

Increased surface area of the MgO-nanoparticles enhancing their dispersion and strengthening their crosslinking in the CMC-Starch polymer blend

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Peaches’ lifespan

Peach is one of the most well-liked and commercially significant fruits in the world. Every seven days during the storage period, the visual appearance, a crucial indicator of quality, was scrutinized to determine the possible efficacy of (CMC-g-Starch-MgO) edible nanofilm surface coating in increasing peach shelf life.

Three sets of peaches were employed. The first set was untreated and left as a control. The second was placed in a container with an edible film exposed to radiation (CMC-g-Starch). Irradiated edible nanocoating (CMC-g-Starch-MgO) was applied to the third group's surface. On day 0, all sets had a brilliant yellowish-brown tint and identical features (Fig. 7).

Fig. 7
figure 7

Mechanical characteristics of the irradiated CMC-g-Starch-MgO nanocomposite film. (A) At different MgO-nanoparticles sizes, (B) At different MgO-nanoparticles concentrations, and (C) At different Gamma irradiation doses

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During day 7, the “control” sets darkened and displayed a small amount of surface fungal degradation, an infection symptom. However, the other two samples exhibited no mold development and no colour change.

During day 14, “control” sets showed tissue becoming softer, darkening, and mold progression. They were destroyed, had a watery surface, and had turned dark grey from mold progression. In contrast, peaches covered in irradiated CMC-Starch-MgO edible nanocoating showed less degeneration than peaches packed with the prepared (CMC-Starch) film.

Moreover, the edible (CMC-g-Starch-MgO) irradiation nanocoating demonstrated better performance in extending the lifespan of peaches.

Peaches' colour plays a significant role in how well consumers will accept them as a product. The possible anti-bacterial activity of MgO is one of the likely mechanisms that explained the effectiveness of (CMC-g-Starch-MgO) edible nanocoating in increasing the shelf-life of Peaches. Several studies have suggested various ways by which MgO can prevent fungus growth.

Additionally, the FDA authority accepts the usage of MgO as a food grade. The researchers previously revealed the developed MgO nanofilms' anti-bacterial efficiency UV prevention competencies [30].

Conclusion

Swelling behaviour, FT-IR, and TEM were used to characterize active edible nanofilms of CMC-Starch-MgO. The influence of varying particle size and concentration of MgO and different irradiation doses on the film characteristics was investigated. The mechanical characteristics of the blend nanofilm developed by increasing MgO-nanoparticles levels up to 2.5 wt%, which might be attributed to the reinforcing action of MgO-nanoparticles in the prepared nanofilm. It was also figured out that the maximum degree of tensile degree of strength and the lowest percentage of elongation were obtained at 20 kGy, which had the minor average of MgO-nanoparticles diameter (Fig. 8).

Fig. 8
figure 8

TGA thermograms curve of the (CMC-Starch) film and the irradiated (CMC-g-Starch-MgO) nanocomposite films at 10 and 20 kGy doses

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They were considering the findings that at gamma radiation 20 kGy, the mechanical properties of CMC-Starch-MgO nanofilms were enhanced. This is because the matrix's crosslinking reaction bounds the motion of the polymeric nanofilm versus the level of applicable forces. By increasing the radiation dose, it was found that irradiated samples became more thermally stable. Additionally, the irradiated CMC-Starch-MgO nanofilm experienced less weight degradation than the unirradiated CMC-Starch film, demonstrating that the irradiation process and MgO incorporation significantly affected the film's thermal stability. Gamma irradiation which was used in the preparation of CMC-Starch-MgO edible nanofilm, also prolonged the lifespan of peach fruits and showed resistance to several pathogenic bacteria, including Pseudomonas aeruginosa and Staphylococcus aureus. It can be said that CMC-Starch-MgO edible film may be ideal for use in future active food packaging.

Availability of data and materials

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request. All data generated or analyzed during this study are included in this manuscript article.

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  1. Radiation Research of Polymer Chemistry Department, National Center for Radiation Research and Technology, Egyptian Atomic Energy Authority, Cairo, Egypt

    Maysara E. Aboulfotouh

  2. Radiation Chemistry Department, National Center for Radiation Research and Technology, Egyptian Atomic Energy Authority, Cairo, Egypt

    Hussein El-shahat Ali

  3. Chemistry Department, Inorganic Division, Faculty of women for arts, science and education, Ain Shams University, Cairo, Egypt

    Maha R. Mohamed

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Maysara E. Aboulfotouh 1, and Hussein El-shahat Ali 2 Did Preparations, characterization, and Discussion and Maha R. Mohamed wrote the main manuscript, part of the discussion, and prepared figures.

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Aboulfotouh, M.E., Ali, H.Es. & Mohamed, M.R. Nano-modifications of edible materials using ionizing radiation for potential application in active food safety. Functional Composite Mater 5, 8 (2024). https://doi.org/10.1186/s42252-024-00056-4

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