鮮度低下による卵黄膜脆弱化と大腸菌の増殖性

Abstract

Japanese shell egg expire dates are determined by Dr. Humphrey’s formula indicating the date in relation to the storage temperature when bacterial rapid growth starts on the egg yolk (EY) membrane in eggs. The validity of this formula was evaluated in this study. First, Haugh Unit (HU), yolk index (YI) and EY membrane strength were measured for fresh eggs (stored at 5℃ after laying) and for eggs sored at 30℃ for 6 days (within expire date) and for 12 days (beyond expire date). It was confirmed that the freshness as well as EY membrane strength decreased with longer term storage of eggs at 30 ℃. Similarly, the leakage of iron and IgY on the EY membrane increased in the washed solution of the yolk when eggs were stored for longer periods at 30 ℃ beyond their expire dates. Moreover, the E.coli growth test in the washed solution containing leaked yolk components showed that EY of eggs stored for longer periods had a higher increase rate of E.coli compared to fresh eggs. This tendency was the most obvious in eggs stored at 12 days beyond expire date. In conclusion, the validity of Japanese egg expire date based on Dr. Humphrey’s formula was verified by showing rapid growth of E.coli in culture with whole EY separated from stored eggs at 30℃.