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

摘要

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 ℃ and at -21 to -41 ℃, 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 ℃ and -15 ℃, respectively. The commercial cod surimi showed T'_(g1) = -65 ℃ and T'_(g2) = -22 ℃. These were reasonable values in comparison with those of carp surimi- sugar mixtures. From the result, it was suggested that the difference offish 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.