Chicken eggs are popular foodstuff worldwide due to their valuable nutrients, such as complete protein, including all essential amino acids, easily digestible fats, vitamins (A, B₂, B₆, B₉ and B₁₂) and minerals (iron, calcium and potassium) [1]. According to the data provided by FAOSTAT, the production of eggs hen in shell, in 2019, was 83,483,675 tons and, according to a report from the Food and Agriculture Organization of the United Nations, global egg production will reach 89 million tons by 2030 [2]. However, poultry-borne pathogens lead to food poisoning in consumers and considerable egg loss and waste. Especially, Salmonella-contaminated eggs and egg-derived products contribute to many salmonellosis cases [3]. Salmonella strains have been frequently isolated from eggshell pieces and different serovars have been linked with egg contamination [4]. Among the Salmonella strains, Salmonella enterica serovar Enteritidis (S. Enteritidis) is frequently recovered from contaminated grade A eggs.

Shell eggs have been reported as one of the principal vehicles for the transmission of bacterial pathogens [5]. The cuticle on eggshells (the organic layer of freshly laid egg) is damaged during extended storage of the egg, leading to the penetration of pathogens attached to the eggshell surface and in the surrounding environment. Therefore, effective disinfection on eggshells is urgently required to maintain good quality egg products by preventing bacterial contaminants from entering eggs.

Nowadays, several antimicrobial approaches have been reported to disinfect S. Enteritidis in eggshells, including ultraviolet C (200–280 nm) ^[3][6][7][3,6,7], H₂O₂ [8], ozone [9] and slightly acidic electrolyzed water (SAEW) [10], but their applications are limited by disadvantages such as photoreactivation, decolorization in certain products at high doses and harmful effects on human [11]. Blue light (BL), especially in the wavelength range of 405–470 nm, has attracted increasing interest because of its intrinsic antimicrobial property [11]. BL excited the endogenous intracellular porphyrins, leading to the production of highly cytotoxic reactive oxygen species and the following cell damage of bacteria ^[11][12][11,12]. BL is considered to be less detrimental to mammalian cells and human skin cells than ultraviolet irradiation [11]. Moreover, it can penetrate deeper than ultraviolet C [11]. Up to now, BL had been successfully applied in disinfection of some food, including cantaloupe rinds [13], fresh-cut papaya [14], milk [15], cucumbers, processed meat products [16] and packaged sliced cheese [17]. Our previous study demonstrated that methicillin-resistant Staphylococcus aureus and Cronobacter sakazakii were decreased by 6 log CFU/mL and 8 log CFU/mL under 415-nm BL illumination of 80 and 240.48 J/cm², respectively and the outer-membrane damage and lipid oxidation were induced by BL irradiation ^[12][18][12,18]. However, up to now, the efficacy of BL on shell egg disinfection has not been studied. Therefore, the purpose of this research was to verify the effectiveness of BL in inactivating S. Enteritidis on eggshells and to explore the effect of BL inactivating S. Enteritidis in maintaining the freshness and quality of eggs.

The current study evaluated the efficiency of 415-nm BL in egg disinfection and systematically evaluated its influence on egg freshness during 5-week storage. It showed that a BL dose of 360 J/cm² led to a 5.19 log CFU/mL reduction in S. Enteritidis in vitro and 54.6 J/cm² of BL illumination led to a reduction of 3.73 log CFU/eggshell on shell eggs. The remaining S. Enteritidis population on eggshells after BL treatment had no significant growth during the 5-week storage. The investigation also showed that 54.6 J/cm² of BL illumination with applied dose did not have significant detrimental impact on the quality of whole eggs. The dynamic changes of albumen pH were similar in BL-treated and control group. The decreases in egg weight, yolk index, HU and total amino acid contents were slowed down by BL illumination. The current findings suggested that the 415 nm BL could be an effective application of S. Enteritidis decontamination on eggshell with potential of maintaining the quality of egg albumen.