An egg shell emits vivid red autofluorescence by ultraviolet radiation, because of the presence of porphyrin on it. The intensity of the autofluorescence depend on amount of porphyrin on the shell surface. The autofluorescence of a fresh egg is stronger then that of an old one. The degree of freshness of an egg and stored periods can be easily detected using a fluorescence photography by which the change in the color tone at the autofluorescence are observed.
(Research Service Section, Planning and Coordination Division)