Low-temperature transitions in cod and tuna determined by differential scanning calorimetry

Differential scanning calorimetry measurements have revealed different thermal transitions in cod and tuna samples. Transition temperatures detected Lit -11degreesC, -15degreesC and -21degreesC were highly dependent on the annealing temperature. In tuna muscle an additional transition was observed at -72degreesC. This transition appeared differently than the thermal events observed at higher temperatures, as it spanned a broad temperature interval of 25degreesC. The transition was comparable to low-temperature glass transitions reported in protein-rich systems. No transition at this low temperature was detected in cod samples. The transitions observed at higher temperatures (-11degreesC to -21degreesC) may possibly stein from a glassy matrix containing muscle proteins. However, the presence of a glass transition at - 11degreesC was in disagreement with the low storage stability at -18degreesC during practical time Scales. It was proposed that freezing of cod could be associated with more than one glass transition. with a glass transition at a temperature lower than -11degreesC being too small to be detectable with instrument. yet governing important deterioration processes. In order to optimize frozen storage conditions, the relationship between deterioration processes important for preservation of quality and glass transition temperatures still needs to be established. (C) 2003 Swiss Society of Food Science and Technology. Published by Elsevier Science Ltd. All rights reserved.