An autofluorescence spectroscopy method has been used to determine the freshness of fishery products. In Japan, freshness is the primary determinant of acceptability and pricing on the fish market because fresh fish products must be suitable to be eaten raw as sashimi and sushi. The most commonly used method to determine fish freshness involves calculating K-values based on chemical assays of nucleotides compounds, which is destructive and time-consuming. According to researchers from Toyohashi University of Technology, at least one or two days of intensive lab work has been required to identify whether or not a fish sample was fresh before being frozen. Difference in fluorescence signals with changing freshness conditions of frozen fish. Courtesy of Toyohashi University of Technology. Now the team has found that fluorescence signals from examined frozen fish were dramatically different from initial freshness conditions, indicating that those signals could be used to track changes occurring in fluorescent-emitting molecules during degradation of aged fish. "We have found that there are some specific excitation wavelengths at which the detection of freshness of frozen fish could be easily recognized," said professor Shigeki Nakauchi. "The problem is to identify the most efficient emission wavelengths to move the application forward towards the real-time mode for on-line applications." The research team is further developing the system by analyzing excitation-emission matrices of frozen fish of different freshness conditions and measuring their reference freshness values by high-pressure liquid chromatography. The research was supported by the Japan Society for the Promotion of Science and was published in Talanta (doi: 10.1016/j.talanta.2015.05.021).