ESR/Spin Probe Study of Ice Cream
2006
Gillies, D.G. | Greenley, K.R. | Sutcliffe, L.H.
Spin probes based on the 1,1,3,3-tetramethylisoindolin-2-yl structure have been used, in conjunction with electron spin resonance spectroscopy (ESR), to study the physical changes occurring in ice cream during freezing and melting. The ESR measurements allowed the rotational correlation times, (B), of the spin probes to be determined. Two probes were used together in a given sample of ice cream, namely, 1,1,3,3-tetramethylisoindolin-2-yl (TMIO), which samples the fat phase, and the sodium salt of 1,1,3,3-tetramethylisoindolin-2-yloxyl-5-sulfonate (NaTMIOS), which samples the aqueous phase. Data from the TMIO probe showed that when ice cream is cooled, the fat phase is a mixture of solid and liquid fat until a temperature of approximately-60 C is reached. The water-soluble probe NaTMIOS showed that the aqueous phase changes completely from liquid to solid within 1 C of -18 C. On cooling further to -24.7 C and then allowing it to warm to +25.0 C, the rotational correlation times of the NaTMIOS were slow to recover to their previous values. For the lipid phase, (B)298 was found to be 65.7 ± 2.0 ps and the corresponding activation enthalpy, deltaH*, was 32.5 ± 0.9 kJ mol-1: These values are typical of those expected to be found in the type of fat used to make ice cream. The water phase gave corresponding values of 32.2 ± 0.5 ps and 24.5 ± 0.4 kJ mol-1 values, which are those expected for a sucrose concentration of 24%.
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