| Abstract
| - The mobility of solutes in frozen food systems (tuna muscle, sarcoplasmic protein fraction of tunamuscle, and carbohydrate−water) has been studied using the temperature dependence of the shapeof electron spin resonance (ESR) spectra of the spin probe 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPOL). The spin probe was incorporated into the tuna meat from an aqueous solution ofTEMPOL or by contact with a layer of TEMPOL crystals. The melting/freezing of freeze-concentratedsolutes in frozen tuna meat was observed to take place over a range of temperatures from −25 to−10 °C. Lower temperatures gave ESR powder spectra due to the decreased mobility of the spinprobe, and the temperature dependence of the mobility of the spin probe did not show abrupt changesat the glass transition temperatures of the systems. The mobility of nonglass forming solutes isconcluded to be decoupled from the glass forming components. Similar behavior was also observedfor TEMPOL in frozen, aqueous carbohydrate systems. The temperature dependence of the mobilityof TEMPOL in the frozen systems was analyzed using the Arrhenius equation, and the logarithm ofthe Arrhenius preexponential factor τa was found to be linearly correlated with the activation energyfor all of the tuna and carbohydrate samples, indicating a common molecular mechanism for theobserved mobility of TEMPOL in all of the systems. The linear correlation also suggests that theobserved mobility of TEMPOL in the frozen aqueous systems is dominated by enthalpy−entropycompensation effects, where the mobility of TEMPOL is thermodynamically strongly coupled to theclosest surrounding molecules. Keywords: Frozen tuna; ESR; solute mobility; glass transition; melting
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