No abstract

The effect of polyphosphate treatment on thaw drip was determined on six freshwater fish species. No relation could be found between state of rigor and thaw drip in control and treated fillets or increase in weight due to dipping. Thaw drip was reduced by an average of 60% as a result of treatment. The difference in weight between control and treated fillets after thawing averaged 5% or more of the initial weight in favor of the treated products. A difference in taste could be detected in yellow walleye (Stizostedion vitreum) and in whitefish (Coregonus clupeaformis) samples, but preferences were equally divided between treated and untreated samples.

The formation of hypoxanthine in ordinary muscle was followed in 36 individual yellow walleye (Stizosted,ion uitreum) and, in 22 individual whitefish (Coregonus cl'upeaJorm'is) stored in ice. At the time of death, the average hypoxanthine content was approximately the same for the two species (0.25 pmole/g); it increased gradually to 1.52 pmole/gin 22 days and to2.54 pmole/g in 18 days in yellow walleye and in whitefish respectively. The average rate of formation in yellow walleye (0.06 pmole/g per day) was the same as in ordinary muscle of swordfish; the rate of formation in whitefish (0.13 pmole/g per day) was slightly higher than that of Atlantic salmon, but lower than that of haddock, petrale sole, and several other marine species. Large variation in rate of formation was noticed between individual yellow walleyes. The average hypoxanthine content of both yellow walleyes and whitefish taken as groups was found to be proportional to the number of days in storage. No difference in average rate of formation was noticed between whitefish fillets from opposite sides of the fish, nor between fresh and thawed fish. The hypoxanthine content appears to be suitable as an index of freshness for groups of fish, not of individual fish. RESUME On a suivi la formation de I'hypoxanthine dans le muscle ordinaire de 36 individus chez le dord (Stizosted,ion vitreum) et 22 individus chez le cordgone (Coregonus ctrupeaformis) entreposds dans la glace. Au ddcbs, la concentration moyenne en hypoxanthine est approximativement la m6me (0.25 pmole/g) chez les deux espdces. Au cours de I'entreposage elle augmente graduellement pour atteindre 1.52 pmole/g en 22 jours et 2.54 pmole/g en 18 jours respectivement chez le dord et le cordgone. Le taux moyen de formation chez le dor6 (0.06 pmole/g par jour) est le m6me que dans le muscle ordinaire de I'espadron; le taux moyen chez le cordgone (0.13 pmole,/g par jour) est ldgbrement supdrieur i celui du saumon atlantique, mais infdrieur d ceux de I'aiglefin, de la plie p6trale, et de plusieurs autres espbces marines. Le dord ddmontre une grande variation du taux entre individus. Le contenu moyen en hypoxanthine chez le dor6 et chez le cordgone augmente proportionellement avec le nombre de jours en entreposage dans la glace. Le taux moyen de formation a e#. b m@me pour les filets des c6tds opposds du poisson et le m6me aussi pour le poisson frais et le poisson ddgel6. Pour ces deux espbces de poisson d'eau douce, le contenu en hypoxanthine semble 6tre un bon indice de fraicheur pour des groupes de poisson, non pour les individus.