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

Abstract

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 °C and at −21 to −41 °C, depending on type and the sugar content of samples. These glass transition temperatures were denoted as T g 1 ′ and T g 2 ′ , respectively. With increasing sugar content, the T g 1 ′ and T g 2 ′ of the samples increased and decreased, respectively. At each sugar level, the T g 1 ′ and T g 2 ′ of carp surimi–trehalose mixtures were higher than those of the other mixtures. From the sugar content effects on T g 1 ′ and T g 2 ′ , the T g 1 ′ and T g 2 ′ of the carp surimi without sugar were estimated to be −55 to −65 °C and −15 °C, respectively. The commercial cod surimi showed T g 1 ′ = - 65 ° C and T g 2 ′ = - 22 ° 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 g 1 ′ and T g 2 ′ 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.