Glass transition poperties of frozen and freeze-dried surimi products: Effects of sugar and moisture on the glass transition temperature

Frozen surimi mixtures containing four types of sugar (sorbitol, glucose, sucrose, and trehalose) and freeze-dried surimi-trehalose mixtures were made from live carp, and their glass transition properties were investigated by differential scanning calorimetry. For comparison, a commercial frozen cod surimi was also investigated. The frozen carp surimi samples showed two freeze-concentrated glass transitions, at -42 to -65 degrees C and at -21 to -41 degrees C, depending on type and the sugar content of samples. These glass transition temperatures were denoted as T-g1', and T-g2', respectively. With increasing sugar content, the T-g1', and T-g2' of the samples increased and decreased, respectively. At each sugar level, the T-g1' and T-g2' of carp surimi-trehalose mixtures were higher than those of the other mixtures. From the sugar content effects on T-g1' and T-g2', the T-g1' and T-g2' of the carp surimi without sugar were estimated to be -55 to -65 degrees C and -15 degrees C, respectively. The commercial cod surimi showed T-g1' = -65 degrees C and T-g2' = -22 degrees C. These were reasonable values in comparison with those of carp surimi-sugar mixtures. From the result, it was suggested that the difference of fish stock did not greatly affect the T-g1' and T-g2' of surimi-sugar mixtures. The moisture content effect on the glass transition temperature of freeze-dried carp surimi-trehalose mixtures was investigated, and a state diagram of the surimi-moisture pseudo-binary system was developed. From the viewpoint of glass transition concept, it is expected that these results are useful in the production and storage of frozen and freeze-dried surimi products. (C) 2006 Elsevier Ltd. All rights reserved.