| Abstract
| - The thermal behavior of fresh tuna muscle, rehydrated freeze-dried tuna muscle, and tunasarcoplasmic protein fraction was studied by three types of differential scanning calorimetry (DSC): conventional DSC, alternating DSC, and sensitive micro-DSC. The relationship between glasstransition temperature, Tg, and water content was established. Only a low-temperature glass transitionwas detected for fresh tuna and freeze-dried tuna rehydrated to high water contents, whereas forsarcoplasmic protein fraction both a low-temperature and an apparent high-temperature glass transitionwere detected for samples of high water content. Construction of the supplemented state diagramsfor whole tuna muscle and for tuna sarcoplasmic protein fraction confirmed the low-temperaturetransition to be glass transition of the maximally freeze-dehydrated phase. The apparent uppertransition of sarcoplasmic protein fraction was shown not to be a glass transition but rather to originatefrom the onset of melting of ice, and the temperature of this event should be denoted Tm‘. The glasstransition temperature and the concentration of the maximally freeze dehydrated tuna muscle are−74 °C and 79% (w/w), respectively. Keywords: Glass transition; differential scanning calorimetry; state diagram; glass relaxation; icemelting; frozen fish
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