Effect of protein coating of hydrolyzed feather on internal quality of eggs during storage period

Introduction: Egg is one of the most valuable food items in the human diet. Several factors, such as diseases, bird age, diet, temperature, humidity, transportation, and storage time can affect the quality of eggs. The longer the storage time, the more CO₂ penetrates the eggshell, particularly at room temperature, resulting in decreased internal quality. Eggs are a perishable product and must be stored in the refrigerator from production to consumption. Refrigeration increases production costs and ultimately leads to an increase in the final product price. Currently, there is a growing interest in developing effective methods to preserve the internal quality of eggs. The use of edible coatings after washing the eggs can help preserve the internal quality of the eggs during long-term storage. Edible coatings are an available technology that is currently used to control moisture, gas exchange, and oxidation processes for many products. The use of suitable active and antimicrobial edible films and coatings can potentially reduce the microbial load of egg surfaces, reduce undesirable changes, and increase their shelf life. Proteins are commonly used as film-forming materials. Proteins that have been previously investigated for egg coating development include whey protein isolate or concentrate, zein, and rice protein concentrate. Chicken feathers are a by-product of the poultry industry and are mostly disposed of without any processing, causing severe environmental pollution. To date, hydrolyzed feather protein has not been reported as an egg coating, so this study investigated the effect of hydrolyzed feather protein coating at two concentrations on the shelf life of chicken eggs under room temperature storage conditions.
Materials and methods: In this study, a total of 120 fresh white-shelled eggs were obtained from Hy-Line W36 laying hens. The eggshells were washed to remove any surface contamination, then the eggs were numbered and randomly selected for each coating method. The samples were divided into three treatments of 40 eggs each treatment in a completely randomized design. The treatments included control (0%, without coating), a coating containing 10% (w/v) hydrolyzed feather, and a coating containing 20% hydrolyzed feather. Pure glycerol (Serva, Germany) was added to hydrolyzed feathers (2% w/v). The feather hydrolyzed protein was prepared at Tarbiat Modares University using alkaline hydrolyzed raw chicken feathers obtained from a commercial broiler slaughterhouse (Iran Borchin, Tehran). The chemical analysis of hydrolyzed feather protein was performed based on standard methods (dry matter, protein, ash, and fat), and the amino acid profile of the protein was also tested. Some nutritional or toxic important minerals were also measured. Egg weight, Haugh units, albumen weight, yolk weight, yolk color, albumen pH, yolk pH, and shell strength were measured during storage weeks 0, 1, 2, 3, and 4.
Results and discussion: According to the data of this study, the height of the egg white and Haugh units in the stored eggs were significantly affected by the experimental coatings (P<0.05). The height of the egg white and Haugh units were significantly higher in the treatment with 20% hydrolyzed protein coating compared to other treatments (P<0.05). The yellowness of the egg yolk was significantly affected by the experimental coatings in the third week (P<0.05). The highest egg quality score was observed in the first and third weeks in eggs with 20% hydrolyzed feather protein coating (P<0.05). The eggshell characteristics were not affected by the experimental coatings. The egg white and yolk percentages were not affected by the experimental coatings. The pH of the egg white in the first and third weeks decreased significantly in eggs with 20% hydrolyzed feather protein coating compared to other treatments (P<0.05). The pH of the yolk was not affected by the experimental treatments. The pH in both the yolk and egg white increased over time. Eggs with coating had significantly less weight loss compared to uncoated eggs (P<0.05). The lowest weight loss was related to eggs with 10% and 20% hydrolyzed feather protein coating, which had a significant difference with uncoated eggs (P<0.05). The weight loss after seven days of storage in uncoated eggs (2.12%) was almost double the weight loss in coated eggs (1.16%). The weight loss after 14 days of storage at room temperature in uncoated eggs (4.21%) was almost double the weight loss in coated eggs (2.35%). The weight loss after 21 days of storage at room temperature in uncoated eggs (6.8%) was almost double the weight loss in coated eggs (3.35%). The weight loss after 28 days of storage at room temperature in uncoated eggs (8.27%) was almost double the weight loss in coated eggs (4.80%). Based on the results of this study, it was found that the use of hydrolyzed feather protein coating can improve the internal quality of eggs during the storage period. For future research, it is recommended to conduct further studies on the effect of hydrolyzed feather protein coating on the quality characteristics of eggs during storage. Previous studies have been conducted on improving the internal quality of eggs during storage using protein coatings with different hydrolysis. Some of these studies have shown that protein coating with hydrolysis can significantly improve the quality characteristics of eggs. Additionally, some studies have been conducted on the effect of protein coating using different proteins such as rice protein, meat protein, whey protein isolated, or whey protein concentrate and zein.
Conclusions: There was no significant difference in weight loss between 10% and 20% hydrolyzed feather protein coverage in different weeks, but the 10% hydrolyzed feather protein coverage provided better protection against weight loss. Since weight loss is mainly due to eggshell water evaporation, it was observed that despite being thinner, the 10% hydrolyzed feather protein coverage provided better protection compared to the 20% hydrolyzed feather protein coverage. Therefore, the use of coverages during egg storage can increase shelf life while maintaining egg quality.