Influences of washing with sodium hypochlorite sanitizer, UV irradiation, and storage temperature on shell egg quality during storage

• Main Authors: I-Chi Chen, 陳翊綺
• Other Authors: Fa-Jui Tan
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/gk426k

碩士 === 國立中興大學 === 動物科學系所 === 106 === Shell eggs are occasionally contaminated by feces, thus leading to the exhibiting of some microorganisms on the surfaces of shell eggs. Some pathogens may enter into eggs from shells. Consumption of those contained eggs, particularly the eggs without washing and raw ones might exhibit a health hazard to consumers. Shell egg cleaning process commonly include physical brushing, sanitizing, and rinsing with running water. Previous studies indicated that sodium hypochlorite (NaOCl) and ultraviolet (UV) irradiation significantly inhibited and sanitized the growth of microorganisms. The objective of the 1st part of the study was to compare the influences of washing, sanitizing with NaOCl and UV irradiation on the quality of eggs stored at different temperatures for 4 weeks; the objective of the 2nd part of the study was to compare the influences of different concentrations of NaOCl and UV irradiation on the quality of eggs stored at refrigerated temperatures. For the 1st part, the results show that the values of water temperatures and free available residual chlorine contents collected from the outlets of washing machines close to the setting ones and conformed to the regulation of Certified Agriculture Standards. The total plate counts detected on the shells of unwashed (U) were significantly higher than those of the ones washed and sanitized with NaOCl (N), as well as the ones washed and sanitized with NaOCl and UV irradiated (NUV), which had the lowest microbial counts. The total plate counts of the inner contents for all groups were less than 25 CFU/mL of egg content. Scanning electron microscope results show that cuticle covering diminished with storage time, while superior cuticle coatings were observed on the ones without washing then stored at 7oC (UC) and 25oC (UR), thus leading to less increases in air cells. The similar change pattern of hydroxyl group intensity detected on the eggshell was also observed, while no significant difference was observed for the eggshell thickness and strength (P > 0.05). After 4-week storage, the performance of Haugh units, pH values and moisture content of albumin, thick albumin ratio, and yolk index of samples stored at 7oC (UC, NC, and NUVC) were superior significantly (P ＜ 0.05) than those stored at 25oC (UR, NR, and NUVR), while no significant difference was observed on the yolk moisture contents of samples (P > 0.05). For the 2nd part, the results show that the values of water temperatures and free available residual chlorine contents collected from the outlets of washing machines close to the setting ones. The total plate counts detected on the shells of unwashed (U) were significantly higher than those of the other treatments, while ones washed and sanitized with NaOCl and irradiated with UV decreased the microbial loads. No significant difference was observed for the eggshell thickness and strength (P > 0.05). The size of air cell increased significantly with storage time, while less increase was observed for the ones without washing. UV irradiation increased the b* values of eggshell (P ＜ 0.05), but for L* values and a* values no significant differences were observed between treatments. After 4-week storage, the Haugh units of samples remained at USDA AA grade, while the yolk index decreased slightly. The pH values of albumin and yolk increased significantly with storage time and no significant differences were observed between treatments. The albumin moisture contents increased with storage time with significant differences between treatments. For the functionality, albumin foaming ability, albumin foaming stability and yolk emulsion capacity were not significantly different between treatments due to the concentrations of NaOCl and UV irradiation (P > 0.05). In conclusion, it is suggested that shell eggs should be washed and sanitized with 50 ppm NaOCl, irradiated by UV, and then storage at refrigerated temperatures in order to maintain the quality as well as the consumption safety.