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De brekingsindex van het oogvocht als objektieve kwaliteitsmethode voor vis
Vyncke, W. (1965). De brekingsindex van het oogvocht als objektieve kwaliteitsmethode voor vis. Meded. Rijksfac. Landbouwwet. Gent 30(4): 2027-2035
In: Mededelingen van de Rijksfaculteit Landbouwwetenschappen te Gent. Rijksfaculteit Landbouwwetenschappen: Gent. ISSN 0369-1721, more

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Keywords
    Gadus morhua Linnaeus, 1758 [WoRMS]; Molva byrkelange (Walbaum, 1792) [WoRMS]; Pleuronectes platessa Linnaeus, 1758 [WoRMS]; Sebastes marinus (non Linnaeus, 1758) [WoRMS]; Marine

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Abstract
    The possibilities of the refractive index (RI ) of the eye fluid as a freshness test for fish were investigated. Procedure details were studied in order to improve the usefulness of the method. The following fishes were used : cod (Gadus morhua L), plaice (Pleuronectes platessa L), redfish (Sebastes marinus L) and blue ling (Molva byrkelange).It appears necessary to extract nearly the whole quantity of eye fluid. Checking the RI of left and right eye can be omitted. Centrifuging the eye fluid is not absolutely required but improves readability. Filtration has no practical value. Keeping the eye fluid during 24 hrs at I ° C results only in a very slight increase in RI : if necessary, determinations can be postponed without harm. The temperature of the refractometer must be maintained at 20° C ± 1,5o C. At fairly constant room temperature, no thermostat is required for routine analyses. A handrefractometer appears to be of little use.With redfish and blue ling, no satisfactory results are obtained. Spoilage curves of cod and plaice on the other hand agree fairly well with organoleptic judgment. The RI seems to be a useful freshness test with those species. Quality gradings are proposed.Advantages and limitations of the method were investigated. The RI can be determined very quickly with simple apparatus and by non specialised personnel. However, no determination is possible on beheaded of proccssed fish or on fish with very small eyes. As variations among individuals can be large, a sufficient number of fishes should always be taken for analysis.

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