For the past decades, in food packaging, the manufacturing and use of plastic films have grown quickly resulting in serious environmental concerns as resistance to degradation (Muscat et al., 2012). Consumers preferred biodegradable materials in terms of reducing the environmental difficulties related with food packaging. Biopolymer polymers as a raw material for food packaging and preservation have been the subject of research (Persin et al., 2011). Because of its ability to minimize moisture and scent loss, solute movement, water absorption in the food matrix, and oxygen penetration, edible and biodegradable films could be applied as a substitute for synthetic packaging materials (Aider, 2010).

Researches and developments in active food packaging have been focused on bio-based functionalpackaging materials incorporating natural active compounds and ingredients (Leceta et al., 2013; van den Broek et al., 2015; Madureira et al., 2015). Chitosan is a cationic linear polysaccharide with a variable degree of N-acetylation derived from chitin and is widely used in agriculture, food, biomedicine and environmental industry due to the positive charges on its amino groups and the presence of other multiple functional groups (Ding et al., 2014; Junter et al., 2016). Chitosan is the second most abundant biopolymer in nature. It has been determined to have significant film-forming abilities as well as other advantageous properties such as biodegradability, biocompatibility, low oxygen permeability coefficients, good mechanical properties, mucoadhesiveness, and derivability from low-cost biomass (Wu et al., 2013; Szymanska and Winnicka, 2015). In addition, chitosan has a great potential to be used as film material due to its non-toxicity, low permeability to oxygen, biocompatibility and excellent film forming ability under acidic conditions (Bonilla et al., 2014), also antimicrobial and antifungal properties against various groups of pathogenic and spoilage microorganisms (Derelio?lu and Turgay, 2019; Tan et al., 2015).

The chicken egg has almost complete balance of essential nutrients with protein, vitamins, minerals and fatty acids with great biological value with the lowest cost for the low-income population (Menezes et al., 2012). The loss of moisture and carbon dioxide via the shell pores causes quality changes in albumen and yolk as well as weight loss of eggs during storage (Wardy et al., 2011). Film coatings can be inhibited moisture, gas, and aroma transfer from the shell pores. For example, chitosan coating can be preserved the internal quality of eggs without affecting consumer acceptance (Kim et al., 2009).

In this study we aimed to investigate the synergistic effect of chitosan coating prepared with acetic, lactic, propionic, gallic and caffeic acids, on the shelf life of chicken and quail eggs. The objective was to study the effects of different formulations of coatings on the physical, structural properties of chicken and quail eggs.

In this study, chicken eggs were obtained from Kahramanmara? Sütçü Imam University Agricultural Faculty Research and Application Farm, Turkey and quail eggs were obtained from a local producer. All the eggs were obtained daily. The study was conducted in food engineering laboratory of Kahramanmara? Sütçü Imam University, Turkey.

Shrimp shell chitosan was obtained from the (deacetylation grade was 75%) Sigma (C3646). Chitosan was dissolved by using acetic acid (Sigma, 320099), lactic acid (Sigma, 69775) and propionic acid (Sigma, 402907). Gallic acid (Merck, 1.01347.0500) and caffeic acid (Acros, 114930250) were used in the coating formulations as phenolic materials. Chitosan solutions were prepared by dissolving 3 g of chitosan in 100 ml distilled water that containing equally added as 1% of organic acids (AA: acetic acid, LA: lactic acid, PA: propionic acid) and 1 g/chitosan phenolic compounds gallic acid (AA+GA: acetic acid with gallic acid, LA+GA: lactic acid with gallic acid, PA+GA: propionic acid with gallic acid), caffeic acid (AA+CA: acetic acid with caffeic acid, LA+CA: lactic acid with caffeic acid, PA+CA: propionic acid with caffeic acid). The solution was heated (40°C) and agitated constantly for 45 min. Finally, polyethylene glycol added to the solution for elasticity (0.25 ml/g chitosan) and agitated 15 min (No et al., 2002).

Coating treatment and storage of eggs

Eggs were coated in chitosan solution by dipping and allowed to dry. Coating treatment was made two times. After coating, the eggs were allowed to dry before being placed on cardboard egg racks with the little end down and stored at room temperature (24±2°C) (Kim et al., 2009). For determination of weight loss, Haugh unit, yolk index, albumen pH, shell strength and albumen viscosity ten replicates per each treatment were taken weekly for up to 4 weeks at 24±2°C.

Determination of weight loss, Haugh unit, yolk index, albumen pH, shell strength and albumen viscosity

Weight loss (%) of the eggs was calculated according to Alleoni and Antunes (2004). The height of albumen and yolk was measured with a tripod micrometer (Model S-6428, B.C. Ames Inc., Melrose, MA, USA). The yolk width was measured with a digital calliper (General Tools & Instruments, New York, NY, USA). The Haugh unit was calculated according to described by Alleoni and Antunes (2004). The yolk index was calculated as yolk height/yolk width (Bhale et al., 2003). After measurement of Haugh unit and yolk index, the albumen was separated from the yolk. The thin and thick albumen were mixed thoroughly prior to measuring pH with a pH meter. For each coating group, 20 chicken eggs and 60 quail eggs were broken and the part of the albumen was separated from the yolk and placed in the viscometer tube. Measurements were carried out at 20°C at a speed of 30 rpm using the L62 heading. The first measurement was recorded as 20 s and the second measurement was recorded as millipascal seconds from 10 s rotation of the head. Torque was applied between 10-100%.

Mineral analyses

Mineral analyses of the samples were done according to EPA method (1994).

Shell breaking strength

Shell breaking resistance analysis, the strength of the egg, which proved to be a criterion is resistance against breaking. Measured with a texture analyzer (STM-1, Santam Co., Tehran, Iran), kg/m² is expressed as (Ezazi et al., 2021).

Statistical analysis

For internal and external quality of chicken and quail eggs, mean ± standard deviation values were reported based on ten measurements (five eggs/replicate) per treatment. One-way analysis of variance of data was carried out using the IBM SPSS Statistics software (v.24). The difference between pairs of means was resolved by means of confidence intervals using Duncan’s tests; the level of significance was set at P < 0.05.

Albumen pH

The albumen pH can also be used as an indicator of the albumen quality of eggs (Wardy et al., 2011). Freshly laid eggs have an albumen pH value of 7.6 to 8.7 (Waimaleongora-Ek et al., 2009). During storage, carbon dioxide escapes via eggshell pores, resulting in thinning of the thick albumen and an increased albumen pH value up to 9.6-9.7 (Kemps et al., 2007).

In this study, albumen values of chicken eggs coated chitosan groups were significantly (P<0.05) lower than those of non-coated chicken eggs throughout 4 weeks of storage at 24±2°C (Table 4). There were no significant differences (P>0.05) in albumen pH among Ch-PA-GA and Ch-AA-CA coated chicken eggs during 4 weeks of storage.

Table 4 showed that the albumen pH of non -coated quail eggs rapidly increased from initial value of 8.92 to 10.15 after 4 weeks of storage at 24±2°C. However, the albumen pH of quail eggs of coated with chitosan formulations the pH gradually increased from 8.92 to 9.27 (Ch-PA-CA). This implied that chitosan coated groups could be retarded loss of carbon dioxide through eggshell pores by acting as a gas barrier.

In the fifth week of storage at 25°C, Soares et al. (2021) found that albumen pH values above 9 for uncoated eggs. Uncoated eggs had an albumen pH above 9 after 21 days of storage at 25°C, according to Lima et al. (2020).

The release of CO₂ into the environment through the eggshell pores changes the albumen pH over time (Soares et al., 2021). Coatings are effective at delaying this reaction because they operate as a physical barrier, reducing gas exchange between the internal and exterior environments.

Mineral levels

According to Table 5 the coated eggs mineral elements values of mineral elements were higher than the control group. The differences between the values of mineral elements that have been used in the initial experiment thought to be caused by the difference of mineral levels of chicken eggs. Higher values of mineral matter in the coated groups can be explained by the barrier formation properties of the coating material and the reduction of losses.

Shell breaking strength

Analysis of the fracture of the shell that repeated every week for the duration of 4 weeks storage the control group had the lowest value (p<0.05). Addition of phenolic compounds caused higher fracture resistance (Table 6). According to Table 6, Ch-AA, Ch-LA, Ch-PA, CH-AA-GA, Ch-LA-GA, Ch-PA-GA and CH-LA-CA shell coating caused the fracture resistance (p<0.05).

In the poultry industry, shell breaking has generally been associated with significant financial loss. The resistance of eggshells coated with RPC plus propolis was not improved, according to Pires et al. (2019) (5 or 1%).

The authors have not declared any conflict of interests.

This work was supported by KSU-BAP (2014/2-48D).