Concept project proposal for the FAIR programme
F. Sigernes and K. Heia
Norwegian Institute of Fisheries and Aquaculture
N-9005 Tromsų, Norway
A hand-held spectrograph for assessment of fish freshness and quality
During the last decade spectroscopy has become extensively used in the agricultural and food processing industries for measuring protein, moisture, and starch in grain and forage crops. The use of spectroscopy have provided a rapid and sensitive method for analysis of organic materials with little or no sample preparation. Despite that spectroscopy has gained a foothold as a quantitative method in food analysis, relatively little is known concerning the applicability in fish analysis.
Recent measurements conducted at Fiskeriforskning shows that VIS/NIR spectroscopy may indeed serve a tool to assess freshness of cod fillet. A correlation coefficient of 0.95 has been found between predicted and stored time on ice. The method is based on the simple fact that organic molecules absorb light. The absorption bands are the results of overtones or combinations of overtones originating in the fundamental mid-range infrared region of the spectrum. Especially, overtones due to hydrogenic stretching vibrations or combinations involving stretching and bending modes of C-H, O-H, N-H or C=O groups are common. These reactions are dependent on time and temperature. A spectroscopic measurement will detect these changes as a function of time and can be used as a tool to assess freshness. Since fish muscle is highly absorbing / opaque / cloudy an approach called Diffuse Reflectance also known as Transflection will be used. In this mode, monochromatic light strikes the fillet perpendicular to the fillet surface. The light then penetrates the fillet and is absorbed and diffusely reflected in all directions. It is the the diffuse back-scattered light of the fillet we detect.
We suggest to design and test a small handheld spectrograph to operate in Transflection mode. The spectra obtained by this instrument will be compared by existing instrumentation, the fairly large sized NIRSystem 6500, in order to construct and calibrate models which assess freshness and quality.
For more information on instrumental setup and results so far:
- Fishtime www-page
- Paper: Concerted Action in Nantes, France 1997
- Karsten Heia
- Fred Sigernes