Development of Edible Coatings Based on Different Biopolymers to Enhance the Internal Shelf-Life Quality of Table Eggs

Abstract

Fresh hen eggs constitute a perishable food and are widely consumed worldwide because of their nutritional value. The eggshell is a natural barrier that protects the egg. However, it is very porous and fragile, which makes it susceptible to breakage, contamination, and deterioration, affecting its internal quality during storage, reducing the half-life of the egg for consumption, and causing economic losses to producers. This study aimed to evaluate different edible composites based on biopolymers and proteins for their application as coatings for preservation and shelf-life extension. First, 32 formulations were prepared and evaluated on eggs stored at 4 °C and 25 °C for 6 weeks. Subsequently, 11 coating solutions with the lowest weight loss were selected, and 216 eggs were evaluated; the response variables were HU, YI, and yolk pH and white pH during weeks 1, 3, and 6 of storage. Finally, four formulations, biobased in chitosan, pectin, and alginate derivative composites, presented the highest internal quality results for at least 3 weeks compared with uncoated eggs. These results expand the range of biopolymers available for use as egg coatings compared with the currently used chitosan, as their production process is less expensive than that of chitosan and more attractive to the poultry industry.

1. Introduction

Eggs are important food resources worldwide due to their nutritional properties as excellent sources of essential proteins, lipoproteins, carbohydrates, fats, vitamins, and minerals [1,2]. They are also used in the food industry for their multifunctional properties, such as foaming, gelling, and emulsifying agents. The poultry industry produced over 87 million tons of table eggs in 2020, with production estimated to reach 95 million tons in 2030 [3]. Food and Agriculture Organization (FAO) projections suggest that global egg consumption will increase from 6.5 to 8.9 kg per person per year by 2030 in developing countries and from 13.5 to 13.8 kg in industrialized countries [4].

The shell, the natural protective covering of the egg, is an important external barrier for the egg. However, its fragility and the large number of pores it contains make it highly susceptible to breakage and deterioration, affecting its internal quality during storage and reducing the shelf-life of eggs [5,6]. This characteristic harms economic losses in the poultry industry because egg aging reduces egg quality and consumer acceptance, increasing the possibility of contamination risk and health problems [7]. Shell breakage, contamination by microorganisms, and aging during storage cause economic losses, which are estimated to constitute 10% to 15% of the total production of table eggs [8].

Many research groups have evaluated low-cost methods to improve the shelf-life and preservation of eggs. A promising alternative is the use of edible coatings on eggshell surfaces, especially the use of natural polymers to make coatings that act as gas exchange barriers [9]. In addition, these kinds of compounds can be applied to different foods, providing protection against aging, and can also act as vehicles for additives such as essential oils, extracts of plants, vitamins, and active molecules, which act as antioxidants, antimicrobial agents, colorants, etc. [10]. The general composition of coatings includes a variety of biomolecules, such as polysaccharides, proteins, and lipids, in combination with a plasticizer, glycerol or sorbitol; molecules need to be incorporated into the formulation to provide flexibility since the hydroxyl groups present in their structure interact with the free functional groups of the polymer [11,12]. Polysaccharides, which can inhibit moisture and gas exchange, are the most commonly used biopolymers in edible coatings, but their hydrophilic properties provide them with a poor barrier to water vapor [13], which limits their competitive application in edible coatings. To overcome this drawback, polysaccharides are combined with other polysaccharides, proteins, or lipids to improve their mechanical properties. The mixtures of these substances are called composites, which present advantages because multicomponent formulations can work together and improve the shortcomings of coatings when only one polymer is used. To improve their barrier properties, the compounds developed in the present study were blended with different polymers that have been reported to have good barrier properties on their own. In this way, the shelf-life of the egg was extended for a period of six weeks at two different temperatures, whereas other studies obtained satisfactory results for up to four weeks or up to six weeks.

Studies have shown that the use of coatings can maintain the internal quality of table eggs during storage, increasing their shelf-life [14,15,16]. Some polysaccharides and proteins are used in fresh egg coatings to increase shelf-life and avoid natural deterioration; among them are chitosan [7,16,17], cellulose derivatives [18], or proteins, such as whey protein [19], rice [16], and chickpea isolates [20]. Previous studies have shown that the use of protein/polysaccharide composites, mainly chitosan, in fresh egg coatings can maintain internal quality during 6 weeks of storage under refrigeration [19] or at room temperature [16,21]. Nevertheless, there is very little information demonstrating the efficiency of different combinations of polymers/proteins/plasticizers. Therefore, the objective of this study was to evaluate different composites based on biopolymers/proteins for use in coating solutions as alternatives to extend the shelf-life and preservation of table chicken eggs at refrigeration (4 °C) and room (25 °C) temperatures.

2. Materials and Methods

2.1. Preparation and Application of Coating Solutions

Seven food-grade biopolymers in powder form were used: chitosan (medium molecular weight, 300–1000 cP, Mw 1,250,000, Pochteca, CDMX, México), aloe (obtained and lyophilized from Aloe barbadensis), pectin (Deiman, El Paso, TX, USA), sodium alginate (Deiman, El Paso, TX, USA), amylopectin from maize (Sigma-Aldrich, Saint Louis, MO, USA), starch, and carboxymethyl cellulose (Deiman, El Paso, TX, USA), and three proteins—gelatin (290 bloom, G.P. 28 Duché, CDMX, México), whey (Pochteca, CDMX, México), and casein (Pochteca, CDMX, México)—and 2 plasticizers—glycerol (gly) (Sigma-Aldrich, Saint Louis, MO, USA) and sorbitol (sor) (Sigma-Aldrich, Saint Louis, MO, USA) —were evaluated in different combinations, resulting in a total of 32 coating formulations designated F1 through F32. The information described for each formulation is shown in

Table 1. Descriptive summary of the composition of each coating formulation from F1 to F32 for fresh egg preservation.

Formulation	Polymer (w/v %)							Protein (w/v %)			Plasticizer (w/v %)
	Chitosan	Aloe	Starch	Pectin	Alginate	CMC	Amylo	Gelatin	Casein	Whey	Sor	Gly
F1	3	-	-	-	-	-	1	-	3	-	2.5	-
F2	3	-	-	-	-	-	3	-	3	-	2.5	-
F3	2	-	2	-	-	-	-	-	-	2	-	2.5
F4	2	-	-	-	-	-	-	1	-	-	2	-
F5	2	-	-	-	-	-	-	-	-	2	2.5	-
F6	2.5	-	-	-	-	-	-	-	-	-	0.25	-
F7	1	0.5	-	-	-	-	-	0.5	-	-	-	2
F8	1	0.5	-	-	-	-	-	0.5	-	-	1	-
F9	1	1	-	-	-	-	-	0.5	-	-	-	2
F10	1	1	-	-	-	-	-	0.5	-	-	1	-
F11	1	1	-	-	-	-	-	-	-	-	-	2
F12	1	1	-	-	-	-	-	-	-	-	1	-
F13	-	-	-	0.75	-	-	-	0.5	-	-	-	2
F14	-	-	-	0.75	-	-	-	0.5	-	-	1	-
F15	-	-	-	-	0.75	-	0.5	0.5	-	-	1	1
F16	-	-	-	-	0.75	-	0.5	0.5	-	-	1	-
F17	-	-	-	-	0.5	-	0.5	0.5	-	-	-	2
F18	-	-	-	-	0.5	-	0.5	0.5	-	-	1	-
F19	-	-	0.5	-	0.75	-	-	0.5	-	-	-	2
F20	-	-	0.3	-	0.5	-	-	0.5	-	-	-	2
F21	-	-	0.75	-	0.75	-	-	0.5	-	-	-	2
F22	-	-	0.75	-	0.5	-	-	0.5	-	-	1	1
F23	-	-	-	-	-	0.75	0.5	0.5	-	-	0.8	-
F24	-	-	-	-	-	0.75	0.5	0.5	-	-	1	-
F25	-	-	-	-	-	0.5	0.5	0.5	-	-	-	2
F26	-	-	-	-	-	0.5	0.5	0.5	-	-	1	-
F27	-	-	-	-	0.75	-	-	0.5	-	-	-	2
F28	-	-	-	-	0.75	-	-	0.5	-	-	1	-
F29	-	-	-	-	0.5	-	-	0.5	-	-	-	2
F30	-	-	-	-	0.5	-	-	0.5	-	-	1	-
F31	-	-	-	-	-	0.75	-	0.5	-	-	-	2
F32	-	-	-	-	-	0.5	-	0.5	-	-	-	2

(-) The symbol indicates the absence of a compound in that formulation. CMC refers to carboxymethyl cellulose, and Amylo refers to amylopectin.

. The polymers, proteins, and plasticizers used to develop the 32 coatings were selected on the basis of previous formulations obtained by the research group. The biopolymers were dissolved in an aqueous phase, heated at 80 °C with a magnetic stirrer for 10 min, and then decreased to 30–35 °C while agitated after the plasticizer was added.

Each formulation and control without coating were evaluated in quadruplicate. A total of 460 fresh eggs were used, which were supplied by a local farm located in Santa Inés Tecuexcomac, Tlaxcala, México. All eggs were obtained on the day of laying and processed the same day to maintain the characteristics of a fresh egg. According to their characteristics, all the units were classified as Grade AA [22].

Because the eggs contained dirt and fecal matter, they were washed before coating. Washing can have negative effects if it is not performed correctly, as washing the egg surface removes the natural murein cuticle of the egg, increasing the porosity of the eggshell [23,24]. For this reason, washing was carried out with a 5% (v/v) water/chlorine solution at a temperature of 38–40 °C. After the disinfectant solution was prepared, a towel was moistened with this solution, and the entire surface of the egg was cleaned and allowed to dry for 1 min with a fan, taking care not to exceed the humidity of the eggshell to prevent microorganisms from penetrating inside the egg. After washing, the samples were weighed and labeled, and the coating was sprayed twice [25]; a total of 1 mL per unit was used, after which the samples were dried with a fan for 30 min. The samples were divided into two different treatment groups: 4 °C and 25 °C. All formulations and the uncoated control were subsequently analyzed at weeks 1, 3, and 6, and different parameters were determined to evaluate the efficiency of the biofilms.

2.2. Screening of Coatings on the Basis of Water Loss

Initially, screening was performed with the 32 coatings applied to the eggs as described above. The response variable was weight loss through the eggshell after 6 weeks of storage. The 32 formulations and uncoated control treatments were evaluated at 4 °C and 25 °C. Four eggs per treatment were evaluated and measured with a digital electronic balance (OHAUS PA1602C, CDMX, México). The weight loss percentage of the eggs during storage was calculated by subtracting the final weight (final day) from the initial weight (day 0) and dividing by the initial weight of each egg [26].

$$weight loss \left(\%\right)={\displaystyle \frac{\left(final weight-initial weight\right)}{initial weight}}\times 100$$

(1)

All formulations that did not show significant differences from the uncoated control were discarded, whereas those that showed protection against dehydration were evaluated for other quality criteria described below.

2.3. Egg Quality Determination

2.3.1. Haugh Unit (HU)

Egg white height and egg weight were measured after 6 weeks of storage for all the treatments. The height of the albumen thickness was measured three times with a digital caliper (Neiko 01407A, Corona, CA, USA), and the weight was calculated as described above. These values were used to calculate the HU value [21,27].

$$HU=100\times log log \left(h-1.7G^{0.37}+7.6\right)$$

(2)

where h represents the height of albumen thickness, expressed in mm, and G represents the mass of the whole egg (g). Eggs were graded by the USDA scale according to the HU values: AA (HU > 72), A (HU = 71 − 60), B (HU = 59 − 31), and C (HU < 30) [28].

2.3.2. Yolk Index (YI)

In 1930, Sharp and Powell [29] reported a procedure for determining a value that they called YI; this value is used to determine the quality of the fresh egg by the characteristics of the egg yolk [30]. The formula used to calculate the YI relates the height and width of the yolk without removing it from the albumen.

$$YI={\displaystyle \frac{height of yolk}{yolk diameter}}$$

(3)

YI expresses the relationship between the height and width of the yolk, so it was calculated as the yolk height divided by the yolk width. Yolk height and width were measured with a digital caliper (Neiko 01407A, Corona, CA, USA) after 6 weeks of storage. A fresh egg of good quality has a yolk index of up to 0.38.

2.3.3. Air Chamber

To measure the air chamber formed due to gas exchange through the eggshell, it was necessary to break the eggshells and measure them at three different sites, between the eggshell and the outer membrane where the air chamber was formed, with a digital caliper (Neiko 01407A, Corona, CA, USA).

2.3.4. pH Measurements

After HU and YI were measured, the albumen and yolk were separated by an egg separator, and the pH of each egg was measured via a model 220 Denver Instrument pH meter (Denver Instrument, Denver, CO, USA).

2.3.5. Water Vapor Transmission Rate (WVTR)

The WVTR value was determined via a modified cup method [31] with an analytical balance (OHAUS 2568, CDMX, México). The top of each egg was punched, and the contents were removed. After drying with a fan, the eggshells were coated with coating solutions. These eggshells were then filled with 20 g of CaCl₂ and sealed on top with gauze after being conditioned for 24 h at 25 °C and 65% RH to reach equilibrium [15]. The variation of the eggshell was recorded after 24 h. The WVTR was calculated via the WVTR equation [18]:

$$WVTR={\displaystyle \frac{x}{t\ast A}}$$

(4)

where WVTR is the water vapor transmission rate through a coated eggshell with a coating (g/m²·s). x represents the grams lost/gained, t represents the time in seconds, and A represents the area of the eggshell covered with the coating.

2.3.6. Scanning Electron Microscopy (SEM) of Eggshell Samples

The morphology of the coated eggshell surfaces and cross sections was characterized via a low vacuum scanning electron microscope (SEM, JEOL JSM5900-LV Ltd., Tokyo, Japan) operating at 20 kV. The eggshells were cut into 1 cm × 1 cm squares, embedded on a base, and then sputtered with gold for observation.

2.3.7. Microbiology Test

An important quality test is the evaluation of microbial growth, as it is necessary to determine whether the coatings are able to block the passage of microorganisms into the interior during storage. To carry out the inoculation, eggs freshly coated with the above-mentioned formulations were taken in triplicate and inoculated with a concentration of $1\times {10}^3$ spores/egg in the case of Aspergillus niger and $1\times {10}^3$ CFU/egg for Salmonella spp. bacteria, dried for 30 min in a laminar flow cabinet, and incubated at temperatures of 4 and 25 °C. The incubation time was 3 weeks. Egg breaking was performed under sterile conditions; the egg surface was cleaned, the eggshell was broken, avoiding contact with the outside, and the egg white and yolk were sampled with sterile swabs. The samples were inoculated in Petri dishes with PDA medium for fungi and nutrient agar for bacteria. The Petri dishes were incubated at 30 °C and 37 °C for 5 and 3 days, respectively.

2.4. Data Analysis

All the significant differences in the results for this study were determined via SAS software (SAS 9.0, Cary, NC, USA). Statistical significance was defined at p < 0.05 with an LSD test.

3. Results

3.1. Determination of Weight Loss

Thirty-two formulations were evaluated for their ability to coat fresh eggs, and after 6 weeks of storage at 4 and 25 °C, the coated eggs were weighed. Weight loss is a parameter used to determine the quality of fresh eggs during storage. Edible coatings have the capacity to act as a semipermeable barrier that reduces mass transfer by sealing pores and helps to maintain egg interior quality [32].

The results of the treatments stored at 4 °C revealed that 28 formulations resulted in less weight loss (mean of 1.58% ± 0.16) compared to the uncoated control treatment (3.15% ± 0.27 weight loss), and coating formulations F2, F10, F16, and F31 showed no significant difference concerning the control treatment (p > 0.0001) because the mean value of these four coatings was 2.87% ± 0.34 (Figure 1a). These values are comparable to those of previous studies [33], which revealed an egg weight decrease of 2.1% in starch/CMC/paraffin-coated eggs and 2.8% in the control at 4 weeks of storage under refrigerated conditions.

When the treatments were stored at 25 °C, only 11 formulations demonstrated statistically significant differences from the control (p < 0.0001). The weight loss percentages observed for these formulations were between 7.28% and 9%, whereas the control exhibited a weight loss of 13.28% ± 0.20. In contrast, some formulations presented values that were similar to or greater than those of the control, as evidenced by F1 (15.46% ± 0.21) (Figure 1b). In this way, when we compared the two temperatures evaluated, we found that 17 formulations that performed well at 4 °C were not very efficient at 25 °C, which means that they did not prove to be efficient in blocking the pores [34], demonstrating the barrier effect of edible coatings on the eggs to prevent weight loss. In the fourth week of evaluation, there was a decrease of at least 5% in weight loss with respect to the control.

The temperature and storage time can have a significant effect on the effectiveness of the coatings used. For this reason, eggs coated with each formulation were stored at two different temperatures, and a comparison of the weight loss of each treatment was performed under different temperature conditions for 6 weeks of storage [35]. The results revealed that the weight of the coated eggs was lower than that of the uncoated eggs at both temperatures. This occurred because the coatings function as substitutes for the natural cuticle of the egg, providing a protective effect on the shell surface by partially sealing the pores and preventing gas exchange and weight loss. Our results are similar to those obtained by Kim [24], who evaluated weight loss in washed and unwashed eggs over a period of four weeks at refrigerated and ambient temperatures. These authors reported that storage time and temperature affect weight loss; however, this loss is lower when stored at 4 °C, and the egg cuticle remains present. In our study, the 11 formulations that were effective at 25 °C also performed well at 4 °C; however, the percentage efficiency exhibited disparate values at both temperatures. In most cases, the formulations demonstrated superior efficacy at one of the two evaluated temperatures, except for F8, which showed no significant differences at 4 °C and 25 °C. This formulation was stable to temperature changes and was composed of aloe vera and chitosan biopolymers. Figure 2 shows the efficiency percentage, which was obtained via the control treatment as the zero point for the other treatments, where formulation F13 demonstrated good efficiency at 4 °C but low efficiency at 25 °C. This coating was formulated with only pectin as a biopolymer.

Previous studies demonstrated that eggs coated with a formulation of pectin and glycerol stored at a temperature of 4 °C presented less weight loss than those stored at 25 °C. Under refrigeration conditions, the weight loss was reduced to 2.49% ± 1.32 with respect to that of the control [36]; however, the reported weight loss was greater than the results obtained in this study because F13 and F14, both coatings with pectin, obtained values of 1.3% and 1.4%, respectively, after six weeks of storage under the same temperature conditions.

A study published in 2022 by Esin and Özlem [17] reported that the use of chitosan/lactic acid coatings at a storage temperature of 24 °C resulted in a reduction in weight loss to 41.63% [17]. In contrast to the abovementioned formulation, in our study, the use of formulations based on aloe + chitosan (F8), pectin (F13 and F14), alginate (F29), and carboxymethyl cellulose (F32) resulted in a reduction in weight loss between 30 and 45% compared with the control treatment. Furthermore, the efficacy of our formulations was found to be superior. The natural porosity of eggshells allows for the exchange of moisture and gases with the external environment via evaporation during storage. This continuous exchange affects the shelf-life of the product because weight is related to important quality parameters such as HU [14,37]. Formulations F3, F4, F8, F9, F13, F14, F15, F20, F26, F29, and F32 were selected for further evaluation of quality parameters because they presented significant differences from the control in the weight loss test.

3.2. Determination of HU Values

The most important parameter for evaluating the quality of eggs in the poultry industry is HU [19,34], which is related to albumen height and egg weight [38]. The decrease in HU is determined by structural changes in egg white proteins, mainly ovalbumin, during the aging process [39,40]. The reduced HU value during storage is the result of albumin thinning, which is influenced by the abovementioned changes. Therefore, a high HU value is indicative of a superior-quality egg [34].

The selected formulations were evaluated at weeks 1, 3, and 6 to determine the variation in quality by HU value concerning time and temperature of storage at 4 °C and 25 °C. The results are presented in

Table 2. HU values at 4 and 25 °C in weeks 1, 3, and 6.

Treatment	4 °C			25 °C
	Week 1	Week 3	Week 6	Week 1	Week 3	Week 6
CT	67.0 ± 14 b,A	60.6 ± 7.5 b,A	60.9 ± 1.3 b,A	58.2 ± 6.79 ab,A	34.4 ± 7.8 cd,B	29.7 ± 8 d,B
F3	72.1 ±1.8 b,A	67.1 ± 6.3 b,A	62 ± 1.1 b,A	59.8 ± 2.2 ab,A	52.4 ± 3.6 bc,A	50.2 ± 2 c,A
F4 *	83.2 ± 1.7 a,A	74.3 ± 5.7 ab,A	74.6 ± 1.9 ab,A	70.2 ± 1.6 a,A	68.9 ± 11.6 a,A	62.4 ± 1.6 ab,A
F8	69.7 ±4.2 b,A	64.0 ± 5.4 ab,A	69.6 ± 1.5 ab,A	60.5 ± 1.6 ab,A	50.5 ± 3.1 bc,AB	45.1 ± 4.7 cd,B
F9	74.6 ±5.1 ab,A	73.6 ± 5 ab,A	65.6 ± 1.1 b,A	52.2 ± 3.3 b,A	39.3 ± 1.1 cd,B	19.0 ± 3.7 e,C
F13	75.7 ±5.3 ab,A	68 ± 8.3 ab,A	67.3 ± 3.2 ab,A	56.2 ± 5.6 ab,A	49.7 ± 3.6 c,A	53.2 ± 5.9 c,A
F14	70.9 ± 1.5 ab,A	66.2 ± 0.4 ab,A	63.6 ± 9.6 b,A	59.7 ± 2.1 ab,A	47.7 ± 3 c,B	34.6 ± 0.7 d,C
F15	72.9 ±3.8 ab,A	71 ± 6 b,A	69.2 ± 1.6 ab,A	75.4 ± 1.7 a,A	54.3 ± 5.5 b,B	49.3 ± 1.3 c,B
F20 *	78.0 ±2.3 ab,A	79.2 ± 5.4 a,A	68.7 ± 1.7 ab,A	68.9 ± 9.1 a,A	55.4 ± 7.4 bc,B	61.7 ± 10.5 bc,AB
F26	69.4 ± 2.8 b,A	68.4 ± 1.8 ab,A	65.1 ± 4.9 b,A	54.7 ± 5.3 b,A	47.9 ± 0.4 cd,A	39.9 ± 0.6 cd,B
F29	68.3 ±9.4 b,A	67.4 ± 5.4 ab,A	67.9 ± 1.2 ab,A	68.5 ± 7.7 a,A	59.8 ± 3.2 ab,AB	51.8 ± 3.9 c,B
F32	78.6 ± 2.1 a,A	72.6 ± 1.9 ab,A	69.7 ± 2.1 ab,A	59.6 ± 1.1 ab,A	52.4 ± 3.1 bc,A	28.5 ± 7.8 d,B

Different letters indicate a significant difference (p < 0.05), small letters indicate a difference according to the treatment during the week, and large letters indicate a difference between the treatments for 6 weeks; ±: standard deviation. * Indicates that the formulation obtained better results than did the other formulations at both temperatures.

, which shows the change in HU values in coated eggs at three different times. The initial HU value, determined immediately after the application of each formulation (day 0), was 80.4 ± 3.41, indicating that the eggs were AA grade quality according to the scale established by the USDA [22].

The analysis conducted at 4 °C revealed that the uncoated control presented a decrease in score from 80.4 to 60.6 ± 7.5, resulting in a reduction from Grade AA to Grade A after the third week of storage and maintaining this grade up to the sixth week (60.9 ± 1.3). Similarly, two formulations, F3 and F14, were not significantly different from the control, with values of 62 and 63.6, respectively. Therefore, neither formulation was functional for storage at 4 °C. On the other hand, F4, F8, F13, F15, F20, F29, and F32 presented significant differences in their ability to protect eggs. Among these formulations, F4 demonstrated the most effective preservation of egg quality, maintaining the AA quality of eggs after six weeks of storage. Similar results to those reported in our study were reported by Biladeau et al. [19], who reported a value of 68.6 HU in control eggs after six weeks of refrigerated storage, indicating that Grade A quality and eggs coated with soy protein isolate demonstrated the capacity to maintain Grade AA quality during the storage period.

A comparison of the treatments at 25 °C revealed that all the treatments were affected by the increase in temperature. From week 1 onward, there was a notable decline of at least 5 points in the HU value, with the best formulation (F15) exhibiting a decrease of at least 5 points and the worst formulation (F9) showing a reduction of 28.2. After six weeks, the HU value of the control treatment decreased from 80.4 to 29.7, which represents a significant deterioration in quality. A decrease in quality means that a decrease from AA to Grade C is no longer deemed acceptable for consumption because of the elevated sanitary risk that it represents [28]. Similarly, the quality of the two coatings, F9 and F32, decreased from AA to C compared with that of the control. The coatings lowered the scores from 80.4 to 19 ± 3.7 and 28.5 ± 7.8, respectively. Moreover, significant differences were observed in the performance of coatings F3, F4, F13, F15, F20, and F29 compared with that of the control. Of these, F4 and F20 presented the best results, decreasing the quality from AA to A during the six-week storage period at 25 °C.

As expected, storage time and temperature are directly related to egg aging, an effect observable in the control treatment. However, the coatings effectively mitigated the quality loss. In the analysis, formulations F4, F13, F15, F20, and F29 were rated the highest in the quality tests, with F4 and F20 performing best in the HU measurements. This protection can be attributed to the composition of these treatments: chitosan for F4 and a starch/alginate composite for F20. These results highlight the importance of the polymer in each formulation. Previous studies have reported the efficacy and widespread use of chitosan in various coating and packaging formulations [17,21]. In contrast, for starch and alginate, their effectiveness is greater in composite form than individually, as properties such as flexibility, permeability, and polymer network cross-linking are enhanced [18,41].

3.3. Determination of the YI Parameter

The yolk index is highly important for assessing egg quality and freshness, as it provides insight into the firmness and stability of the proteins that surround the yolk [42]. During the storage period, the proteins that constitute the vitelline membrane, which encases the yolk, undergo a process of bonding loss, thereby enabling water exchange from the albumen to the yolk, resulting in a loss of firmness of the yolk [43]. The spherical nature of egg yolk can be expressed as a YI and is based on the ability to maintain the integrity of the yolk after eggshell breakage [44].

The initial YI value was 0.47 ± 0.02, and the changes in YI for the selected treatments, derived from the water loss results and the uncoated control, are shown in

Table 3. Effects of different coatings on the YI values at 4 °C and 25 °C after 1, 3, and 6 weeks of storage.

Treatment	4 °C			25 °C
	Week 1	Week 3	Week 6	Week 1	Week 3	Week 6
CT	0.44 ± 0.03 ab,A	0.37 ± 0.02 ab,A	0.38 ± 0.01 ab,A	0.26 ± 0.01 b,A	0.20 ± 0.01 b,AB	0.15 ± 0.01 b,B
F3	0.43 ± 0.02 a,A	0.32 ± 0.05 ab,B	0.37 ± 0.06 ab,B	0.36 ± 0.02 a,A	0.32 ± 0.01 ab,AB	0.22 ± 0.01 ab,B
F4	0.43 ± 0.03 a,A	0.42 ± 0.01 ab,A	0.39 ± 0.01 ab,A	0.30 ± 0 ab,A	0.32 ± 0.04 ab,A	0.27 ± 0.04 ab,A
F8	0.39 ± 0.01 ab,B	0.39 ± 0.06 ab,A	0.36 ± 0.01 ab,A	0.36 ± 0.05 a,A	0.28 ± 0.07 ab,AB	0.22 ± 0.07 b,B
F9	0.39 ± 0.02 ab,B	0.40 ± 0.009 a,A	0.31 ± 0.02 b,A	0.32 ± 0.02 ab,A	0.21 ± 0.01 b,A	0.22 ± 0.01 ab,A
F13	0.44 ± 0.05 ab,A	0.39 ± 0.04 ab,A	0.44 ± 0.02 a,A	0.39 ± 0.03 a,A	0.32 ± 0.01 ab,A	0.23 ± 0.01 ab,B
F14	0.39 ± 0 ab,B	0.31 ± 0.01 ab,A	0.32 ± 0.06 b,A	0.30 ± 0.0 ab,A	0.21 ± 0.04 b,AB	0.16 ± 0.04 b,B
F15	0.41 ± 0.02 ab,A	0.44 ± 0.008 a,A	0.43 ± 0.01 a,A	0.33 ± 0.03 ab,A	0.27 ± 0.03 ab,A	0.31 ± 0.03 ab,A
F20	0.48 ± 0.02 a,A	0.40 ± 0.03 ab,A	0.42 ± 0.004 a,A	0.37 ± 0.03 a,A	0.35 ± 0.01 a,A	0.30 ± 0.01 ab,A
F26	0.44 ± 0.01 ab,A	0.41 ± 0.01 ab,A	0.39 ± 0.01 ab,A	0.33 ± 0.03 ab,A	0.28 ± 0.01 ab,AB	0.17 ± 0.01 b,B
F29	0.42 ± 0.01 ab,A	0.44 ± 0.05 a,A	0.40 ± 0.03 a,A	0.33 ± 0.04 ab,A	0.30 ± 0.03 ab,A	0.25 ± 0.01 ab,A
F32	0.41 ± 0.01 ab,A	0.38 ± 0.01 ab,A	0.39 ± 0.01 ab,A	0.33 ± 0.02 ab,A	0.28 ± 0.01 ab,AB	0.22 ± 0.01 ab,B

Different letters indicate a significant difference (p < 0.05); small letters indicate a difference according to the treatment during the week, and large letters indicate a difference between the treatments for 6 weeks; ±: standard deviation.

. At a temperature of 4 °C, no significant differences (p < 0.05) were found in the treatments over time; however, differences were observed between the treatments in each of the evaluated weeks. In week 1, a statistically significant difference was observed between F20 and all other treatments, including the control. In week three, the values for F9, F15, and F29 exceeded 0.4, which indicates fresh egg values [14,42]. Finally, by the sixth week, formulations F13, F15, F20, and F29 achieved fresh egg scores.

With respect to the control eggs stored at 25 °C, a decrease in YI and HU was observed over time. In contrast, the number of eggs coated with formulations F4, F13, F15, F20, and F29 did not significantly change with increasing storage time (p > 0.05). However, when these same formulations were compared at week 6 with respect to the control, YI was significantly greater (p < 0.05). Similar to our results, Esin and Özlem [17] reported that parameters such as YI and HU values are negatively influenced by storage time, regardless of the use of a coating with chitosan-organic acid composites. Another study using chitosan, lysozyme, and ozone in eggs stored for a period of six weeks reported that coated eggs had higher YI values than did uncoated eggs [32]. These results suggest that the application of coatings can enhance the preservation of yolk and white integrity during storage at different temperatures.

3.4. Measurement of the Air Chamber

The physicochemical and structural changes in the albumen and yolk are due primarily to water and CO₂ exchange with the exterior of the shell. This occurs as a result of the osmotic migration of water, which alters protein structures in the albumin and vitelline membranes [45]; these changes are influenced negatively by the temperature and duration of egg storage [46]. Therefore, it is considered an important parameter to measure inside the egg, and the European Commission Regulation associates the size of the air space with egg freshness, classifying an egg as AA when the air chamber is no larger than 4 mm and as quality grade A when that value does not exceed 6 mm, indicating that a larger air space corresponds to lower egg quality [47].

In this study, the air chamber was measured at different storage times (1, 3, and 6 weeks) in uncoated control eggs and in eggs coated with the different selected formulations, which were stored at 4 and 25 °C as a parameter to determine the efficiency and efficacy of the coatings evaluated to preserve egg freshness (

Table 4. Air chamber measurements (mm) of eggs stored under refrigeration (4 °C) at room temperature (25 °C). Week 1, 3, and 6.

Treatment	4 °C			25 °C
	Week 1	Week 3	Week 6	Week 1	Week 3	Week 6
CT	0.0 ± 0.0 a,C	3.18 ± 0.04 a,B	6.62 ± 0.52 a,A	3.39 ± 0.17 b,C	7.31 ± 0.49 b,B	11.12 ± 1.23 a,A
F3	0.0 ± 0.0 a,C	2.00 ± 0.01 b,B	6.7 ± 0.41 a,A	2.89 ± 0.03 c,C	4.59 ± 0.42 de,B	9.02 ± 1.06 b,A
F4	0.0 ± 0.0 a,C	0.25 ± 0.35 d,B	2.74 ± 0.98 e,A	2.96 ± 0.01 c,B	5.85 ± 0.70 c,A	5.66 ± 1.13 e,A
F8	0.0 ± 0.0 a,C	0.95 ± 1.34 c,B	5.16 ± 1.21 bc,A	3.76 ± 0.06 ab,B	4.72 ± 0.13 d,B	9.26 ± 1.47 b,A
F9	0.0 ± 0.0 a,B	0.07 ± 0.09 e,B	5.82 ± 1.51 b,A	3.16 ± 0.06 bc,C	5.01 ± 0.57 d,B	7.96 ± 1.64 c,A
F13	0.0 ± 0.0 a,B	0.0 ± 0.00 e,B	3.45 ± 0.66 de,A	3.22 ± 0.44 b,B	7.05 ± 0.02 b,A	8.81 ± 1.52 bc,A
F14	0.0 ± 0.0 a,C	1.89 ± 0.42 b,B	6.97 ± 0.90 a,A	3.73 ± 0.39 ab,C	8.12 ± 0.87 a,B	10.87 ± 0.68 ab,A
F15	0.0 ± 0. 0 a,B	0.0 ± 0.0 e,B	2.69 ± 1.08 e,A	3.05 ± 0.08 c,B	4.82 ± 0.09 d,B	8.12 ± 1.58 c,A
F20	0.0 ± 0.0 a,B	0.0 ± 0.0 e,B	4.74 ± 2.09 c,A	4.38 ± 0.05 a,B	5.01 ± 0.17 d,AB	6.4 ± 1.35 d,A
F26	0.0 ± 0.0 a,B	0.0 ± 0.0 e,B	4.37 ± 0.26 cd,A	2.14 ± 0.04 cd,C	5.03 ± 1.17 d,B	8.34 ± 0.28 c,A
F29	0.0 ± 0.0 a,C	0.71 ± 1.01 c,B	4.50 ± 1.33 c,A	0.00 ± 0.00 d,C	3.99 ± 1.40 e,B	6.00 ± 0.01 de,A
F32	0.0 ± 0.0 a,B	0.0 ± 0.00 e,B	3.47 ± 0.64 d,A	3.93 ± 0.11 a,C	5.34 ± 0.89 cd,B	10.12 ± 1.89 ab,A

Different letters indicate significant differences (p < 0.05); small letters indicate differences according to treatment during the week, and large letters indicate differences between the treatments for 6 weeks; ±: standard deviations.

).

During the first week of storage at 4 °C, no effect on the air chamber in treated eggs was observed. Nevertheless, after three weeks, some coatings, including F13, F15, F20, F26, and F32, exhibited no air space. At six weeks of storage, all the coatings allowed for gas exchange, as evidenced by an increase in the air space inside the egg. The F3 and F14 formulations had lengths of 6.7 ± 0.41 and 6.97 ± 0.90 mm, respectively, which were not significantly different from those of the uncoated treatment, which had a length of 6.62 ± 0.52 mm of air space. These findings suggest that these formulations may not be highly effective in minimizing gas exchange through eggshell pores over a six-week storage period. In contrast, formulations F4, F15, F13, and F32 were notably different from the control, with minimum values of 2.74 ± 0.98, 2.69 ± 1.08, 3.45 ± 0.66, and 3.47 ± 0.64 mm, respectively. These coatings also demonstrated the most favorable outcomes in HU assessment. This indicates that there is a correlation between gas exchange and YI and HU [45].

At a temperature of 25 °C, the air chamber had a greater influence on temperature, with the formation of an air chamber observed in the coated treatments from the first week of storage in comparison to the treatments stored at 4 °C, whereas under these conditions in the first week, no air chamber was observed. Moreover, as the time of storage increased, the length of the air chamber increased for all the treatments. Nevertheless, after six weeks of storage, the coated samples presented statistically significant differences (p < 0.05) from the control samples because all of them maintained air space values under the uncoated treatment. Consequently, although the coatings showed significant differences (p < 0.05) in terms of the degree of protection, they all demonstrated the capacity to partially block gas exchange through the shell pores, with formulations F4 and F29 achieving A-grade quality scores [47]. The results obtained for this parameter demonstrate the influence that the storage temperature and the type of polysaccharide used have on the polymeric network formed in each coating [41]. Both factors influence the permeability of water vapor and gases; however, the polymers chitosan (F4) and alginate (F29) presented fewer alterations in their crosslinking, demonstrating good barriers to gas exchange at both temperatures. This result is similar to the observed results of WVP and WVTR because both coatings were less permeable to water vapor.

3.5. Determination of the pH of Yolk and Albumen

The pH increases during the storage period, as reported by different authors [48,49]. This alkalinization disrupts the bicarbonate buffering system, which in turn results in alterations in the proteins present within the egg. These changes result in a transformation of the egg’s characteristics and structure, ultimately manifesting as a watery egg. Some reports indicate that the buffering system can remain stable if the exchange of water vapor and carbon dioxide is reduced [50]. To evaluate the behavior of pH in yolk and albumen with respect to storage time and temperature across the different treatments, the value of pH was determined subsequent to the completion of HU and YI measurements. The reference pH value for a fresh egg (day 0) ranged from 5.9 to 6.2 for the yolk and from 7.6 to 8.0 for the albumen.

Table 5. Effect of coatings on yolk pH values at refrigerated (4 °C) and room temperatures (25 °C) after 6 weeks.

Treatment	4 °C			25 °C
	Week 1	Week 3	Week 6	Week 1	Week 3	Week 6
CT	6.04 ± 0.09 a,A	6.34 ± 0.23 a,A	6.37 ± 0.25 a,A	5.93 ± 0.06 a,A	6.54 ± 0.16 a,B	6.52 ± 0.04 a,B
F3	6.00 ± 0.02 a,A	6.35 ± 0.09 a,A	5.95 ± 0.07 a,A	6.01 ± 0.01 a,A	6.46 ± 0.06 a,B	6.35 ± 0.15 a,B
F4	5.93 ± 0.10 a,A	6.15 ± 0.20 a,A	6.03 ± 0.04 a,A	5.91 ± 0.06 a,A	6.22 ± 0.19 a,A	6.15 ± 0.03 a,A
F8	6.02 ± 0.02 a,A	6.13 ± 0.10 a,A	6.33 ± 0.30 a,A	6.04 ± 0.04 a,A	6.30 ± 0.03 a,AB	6.43 ± 0.03 a,B
F9	6.02 ± 0.02 a,A	6.23 ± 0.03 a,A	6.13 ± 0.13 a,A	6.05 ± 0.02 a,A	6.30 ± 0.05 a,AB	6.83 ± 0.01 a,B
F13	6.03 ± 0.16 a,A	6.35 ± 0.11 a,A	5.98 ± 0.05 a,A	5.99 ± 0.12 a,A	6.37 ± 0.06 a,AB	6.59 ± 0.19 a,B
F14	6.01 ± 0.02 a,A	6.30 ± 0.03 a,A	6.31 ± 0.42 a,A	6.03 ± 0.01 a,A	6.49 ± 0.10 a,A	6.35 ± 0.12 a,A
F15	5.96 ± 0.09 a,A	6.15 ± 0.19 a,A	6.14 ± 0.02 a,A	5.99 ± 0.27 a,A	6.20 ± 0.20 a,A	6.35 ± 0.18 a,A
F20	6.28 ± 0.15 a,A	6.31 ± 0.04 a,A	6.07 ± 0.03 a,A	6.41 ± 0.19 a,A	6.34 ± 0.22 a,A	6.33 ± 0.16 a,A
F26	5.91 ± 0.03 a,A	6.40 ± 0.05 a,A	6.01 ± 0.01 a,A	6.05 ± 0.06 a,A	6.49 ± 0.06 a,AB	6.69 ± 0.21 a,B
F29	5.96 ± 0.06 a,A	5.91 ± 0.07 a,A	6.07 ± 0.03 a,A	5.94 ± 0.09 a,A	6.15 ± 0.15 a,AB	6.45 ± 0.36 a,B
F32	5.97 ± 0.03 a,A	6.20 ± 0.08 a,A	6.59 ± 0.42 a,A	6.07 ± 0.03 a,A	6.31 ± 0.03 a,A	6.39 ± 0.08 a,A

Different letters indicate significant differences (p < 0.05); small letters indicate differences according to treatment during the week, and large letters indicate differences between the treatments over 6 weeks; ±: standard deviations.

presents all the recorded yolk pH values at 4 and 25 °C. At a temperature of 4 °C, no significant differences were observed in the pH change in the yolk with respect to storage time across the different treatments, including the control. This observation is consistent with the results from the other evaluated parameters, indicating that at 4 °C, the egg aging process occurs more slowly. At 25 °C, a notable discrepancy was observed in the pH increase in the control treatment as the storage time increased. A similar outcome was evident in treatment F3, indicating that this formulation was ineffective in reducing gas exchange between the egg and its external environment. This result is consistent with the data from the air chamber, which indicates an increase in the formation of air space beginning in the third week. In contrast, F4 presented the most favorable results, with no significant differences in pH change over the six-week storage period and significant differences compared with the control treatment from the third week.

Table 6. Effect of the coatings on the albumen pH at refrigerated (4 °C) and room temperature (25 °C) after 6 weeks of storage.

Treatment	4 °C			25 °C
	Week 1	Week 3	Week 6	Week 1	Week 3	Week 6
CT	9.38 ± 0.18 a,A	9.39 ± 0.12 a,A	9.22 ± 0.01 a,A	9.25 ± 0.53 ab,A	9.53 ± 0.01 a,A	9.47 ± 0.06 a,A
F3	9.06 ± 0.05 ab,a	9.25 ± 0.04 ab,A	9.22 ± 0.04 a,A	9.14 ± 0.03 ab,A	9.39 ± 0.05 ab,A	9.13 ± 0.05 ab,A
F4	9.09 ± 0.17 ab,A	9.0 ± 0.08 ab,A	9.04 ± 0.06 a,A	9.06 ± 0.26 ab,A	8.69 ± 0.1 b,B	9.03 ± 0.03 ab,A
F8	9.32 ± 0.07 a,A	9.40 ± 0.05 a,A	9.24 ± 0.01 a,A	9.46 ± 0.07 a,A	9.53 ± 0.04 a,A	9.38 ± 0.1 ab,A
F9	9.16 ± 0.11 ab,A	9.23 ± 0.04 ab,A	9.20 ± 0.04 a,A	9.37 ± 0.04 ab,A	9.43 ± 0.03 ab,A	9.42 ± 0.03 ab,A
F13	9.05 ± 0.15 a,A	8.93 ± 0.12 b,A	9.12 ± 0.08 a,A	8.70 ± 0.30 b,B	8.95 ± 0.4 ab,AB	9.45 ± 0.01 a,A
F14	9.39 ± 0.02 a,A	9.35 ± 0.05 a,A	9.15 ± 0.05 a,A	9.43 ± 0.06 a,A	9.47 ± 0.07 a,A	9.42 ± 0.1 a,A
F15	9.34 ± 0.06 a,A	9.13 ± 0.23 ab,A	9.10 ± 0.13 a,A	9.27 ± 0.15 ab,A	9.17 ± 0.09 ab,AB	8.96 ± 0.3 b,B
F20	8.23 ± 0.06 b,B	8.97 ± 0.13 b,AB	9.18 ± 0.01 a,A	8.59 ± 0.35 b,A	8.49 ± 0.65 b,A	8.91 ± 0.1 b,A
F26	9.23 ± 0.15 ab,A	9.39 ± 0.08 a,A	9.10 ± 0.02 a,A	9.34 ± 0.07 a,A	9.48 ± 0.06 ab,A	9.32 ± 0.02 ab,A
F29	9.12 ± 0.35 ab,A	9 ± 0.21 b,A	9.06 ± 0.16 a,A	9.01 ± 0.21 ab,AB	8.85 ± 0.2 ab,B	9.3 ± 0.09 ab,A
F32	9.21 ± 0.03 ab,A	9.3 ± 0.04 ab,A	9.14 ± 0.0 a,A	9.28 ± 0.02 ab,A	9.38 ± 0.02 ab,A	9.23 ± 0.07 ab,A

Different letters indicate significant differences (p < 0.05); small letters indicate differences according to treatment during the week, and large letters indicate differences between the treatments over 6 weeks; ±: standard deviations.

shows the albumen pH after the sixth week at 4 and 25 °C. At 4 °C, the pH behavior of the albumen was comparable to that previously reported for the yolk, with no significant differences observed at week six in any of the treatments. However, there was an increase of at least one unit compared with the value on day 0, which is likely due to the effect of gas exchange on the pH balance of the albumen prior to the yolk [48]. At 25 °C, the formulation with the lowest efficiency compared with the control was F14. In contrast, F20 demonstrated the most stable pH, with a smaller increase than all the other formulations over the six-week storage period. This formulation also received high scores in quality parameters, similar to F4.

Other studies reported an increase in albumen pH values during storage; for example, Saeed et al. [51] reported values ranging from 7.42 to 9.18 over a four-week storage period. Yuceer et al. [32] reported a gradual increase in pH values in their control treatment, increasing from 7.79 to 9.27 over six weeks. In our study, the pH values of the untreated eggs exhibited a similar trend, increasing from 7.98 to 9.47 over the same storage duration. In the treatments where the coatings were applied, the albumen pH was lower than that of the control. The findings of this study indicate that F20 and F15 were the coatings that presented significant differences compared with the control.

3.6. Determination of the WVTR and WVP

The use of coatings in the packaging industry aims to reduce mass transfer, primarily water vapor, between the interior and exterior of food [52]. Previous studies have demonstrated the effective deployment of polymers such as chitosan, starch, CMC, and soy isolates in coating formulations [18,52]. In this study, eggs were coated with different formulations, and a piece of the coated eggshell was used for WVTR and WVP determination. These two parameters are employed to assess the water vapor transmission capacity of coatings [15]. Figure 3 shows these values. The CT (uncoated shell) presented higher values of $71.26 \pm 3.65 \mathrm{g}/\left(\mathrm{d}\ast {\mathrm{m}}^2\right)$ WVTR and $6.82 \pm 0.52 {\displaystyle \frac{\mathrm{g}}{\left(\mathrm{d}\ast {\mathrm{m}}^2\right)}}\ast \mathrm{P}\mathrm{a}$ in the WVP.

In contrast, eggshells covered with different formulations presented significant differences compared with the control (p < 0.05). F29 was the coating with the best results, with $26.88 \pm 2.23 \mathrm{g}/\left(\mathrm{d}\ast {\mathrm{m}}^2\right)$ in the WVTR and $1.57 \pm 0.29 {\displaystyle \frac{\mathrm{g}}{\left(\mathrm{d}\ast {\mathrm{m}}^2\right)}}\ast \mathrm{P}\mathrm{a}$ in the WVP, followed by F4, and F14 presented the worst values of $60.17\pm 5.26 \mathrm{g}/\left(\mathrm{d}\ast {\mathrm{m}}^2\right)$ and $4.64 \pm 0.62 {\displaystyle \frac{\mathrm{g}}{\left(\mathrm{d}\ast {\mathrm{m}}^2\right)}}\ast \mathrm{P}\mathrm{a}$.

These results are consistent with those obtained in the HU and air chamber tests, as water vapor permeability plays a significant role in moisture penetration, reaching the egg interior and subsequently impacting system equilibrium. This, in turn, induces protein modifications and influences HU values [36]. Similar findings have been reported in other studies; Xu et al. [15] demonstrated that using a coating reduced the WVP of the eggshell, with all the treatment values being lower than those of the control. Additionally, Mari et al. [52] conducted WVTR tests and reported low WVTR values for films made with chitosan, a polymer used in F4. They reported that the hydrophobic nature of this biopolymer results in lower WVTR values than those of other biopolymers, such as starch and pectin, which have hydrophilic characteristics.

3.7. Morphology of Eggshells

The structure of the eggshell is highly important for maintaining the internal quality of the egg. With the passage of time and increasing age of the hen, the pores and microfractures may become more apparent. The exchange of gases, such as water vapor and carbon dioxide, occurs more rapidly in eggs with greater porosity, resulting in changes in the macromolecular structures within the egg and, consequently, a reduction in its quality [8,34,53].

Formulations F4 (chitosan), F13 (pectin), F15, F20 (alginate/amylopectin), and F29 (alginate) were observed to maintain acceptable egg quality after 6 weeks of storage. However, we conducted a brief cost‒benefit analysis and reported that chitosan-based coatings such as F4 were the most expensive due to higher polymer costs (from $30 to $80 per kilogram, depending on the quality and supplier), whereas alginate-based formulations such as F29, with lower polymer concentrations used in the formulation and costs ($10 to $25 per kilogram), proved to be more economical without compromising efficacy. This cost-effectiveness is critical for industrial applications to ensure that coatings do not significantly impact the final cost of eggs. These treatments were analyzed via SEM to determine the presence and adhesion of the coating to the eggshell surface. For this purpose, images of both the surface and the cross-section of the eggshell were obtained. SEM images of both the surface and cross-sections of the samples subjected to the aforementioned treatments are displayed in Figure 4. The uncoated eggshell surface (Figure 4a) shows cracks on the surface of the eggshell. In contrast, the internal cross section (Figure 4b) displays the typical arrangement of eggshell layers, namely, the mammillary and palisade layers [8,54]. The presence of a coating layer is indicated by the red arrows in F4, F13, F15, F20, and F29 (Figure 4c,e,g,i,k), demonstrating the presence of a coating layer, marked with red arrows, and surface images show that the cracks in the eggshell were covered by the coatings. Xu et al. [15] reported differences in eggs covered with protein/montmorillonite coatings compared with those covered with uncoated eggs. Formulation F4 exhibited a smooth and homogeneous coating texture on the eggshell surface (Figure 4c), indicating that the polymer effectively blocked gas exchange. This result correlates with the values obtained by F4 in the evaluation of HU, YI, and air chamber parameters at 25 °C, where significant differences were detected compared with those of the other coatings, thereby maintaining good egg quality after 6 weeks of storage. Instead, formulation F29 results in irregular coverage, providing partial sealing of the eggshell cracks. Another study reported a similar behavior [53], in which a chitosan coating was tested on eggs and was found to exhibit polymer fragility due to dehydration. SEM analysis revealed coating loss over storage time, and the same result was observed in our study of F29.

3.8. Barriers to Microorganisms

During the commercialization process, the egg must be stored for relatively long periods, and fungal development is more suited to these humidity and temperature conditions; however, Salmonella spp. are known to be bacteria commonly found in the cloaca of these birds [6]. For this reason, both microorganisms were evaluated.

The results obtained in the Petri dishes revealed that, in none of the coated eggs did the microorganisms manage to penetrate the eggshell, since the plates did not show any growth in the yolk or white samples; in contrast, the control sample allowed the growth of Aspergillus niger in the white samples (Figure 5). Aspergillus contamination inside the egg may have been due to the high concentration of microorganisms on the shell surface, as well as the removal of the cuticle during the washing process, leaving the shell pores exposed and allowing the microorganisms to enter. Several reports have shown that elimination of this external layer favors the growth of fungi, especially those of the Cladosporium genus [55]. On the other hand, some authors mention the use of coatings to reduce food contamination by microorganisms; in the case of table eggs, they have taken advantage of the antimicrobial activity of some polymers, such as chitosan, to prevent bacterial growth [56]. Another study reported that the use of phytochemicals in composites with gum arabic and pectin was effective in reducing the population of Salmonella enteritidis [57].

These results are related to those obtained via SEM since the images show that the coating layer is present in all the treatments after six weeks of storage.

4. Conclusions

The results demonstrated that the coated eggs exhibited superior internal quality compared with the uncoated control eggs over a six-week storage period, as indicated by the HU, YI, and WVTR measurements. On the other hand, coatings provide different degrees of protection during egg aging. This observation was made possible by SEM analysis, and images revealed that the polymers coat the microcracks and pores that are common in the shells. However, some were more easily observed than others were. The coatings were made with different natural polymers, alginate, pectin, and chitosan, which are the better polymers for sealing the pores and extending the shelf-life of table eggs for 6 weeks at 4 °C and 25 °C. The coatings with higher values of internal quality were F4 (chitosan), F13 (pectin), F15 and F20 (both alginate/amylopectin), and F29 (alginate). These results suggest the possibility of the use of new polymers as coatings to increase the shelf-life of eggs.

Compared with other polymers, chitosan is the most widely used biopolymer for the preparation of coatings; however, its cost on the market is one of the highest. In this study, the amount of chitosan used to formulate an efficient coating that meets the requirements of fresh egg preservation was high compared with that of some of the formulations evaluated. Different formulations have been obtained using other, more economical polymers, such as alginate, pectin, and amylopectin, which have similar results to those obtained with chitosan-based formulations. These formulations are a viable alternative for the preservation of fresh eggs that do not have a significant effect on the final price and may be of interest to the poultry industry because they could help reduce losses due to egg spoilage. The improved barrier properties of coatings reduce the risk of microbial infiltration, improve food safety, and minimize health risks.

Further studies are necessary to determine the mechanical properties of the polymers and their interactions to provide different levels of egg quality protection and evaluate their sensorial properties to determine whether the coatings modify the sensory attributes of eggs.