| Research Abstract |
To determine the effect of high-pressure-freezing on quality, gels (egg custard gel, agar, agar with high visco-elasticity, κ-carrageenan, ι-carrageenan, κ-carrageenan+locust bean gum, curdlan, substituted gellan gum and native gellan gum) and egg yolk were frozen at 0.1〜686 MPa at ca. -20℃. After reducing to atmospheric pressure, gels were stored at -30℃ then thawed at 20℃. The amount of drip, texture and structure (cryo-SEM observation) were then compared with gels frozen (-20℃, -30℃ or -80℃) at atmospheric pressure (0.1 MPa). In gels without sugar, frozen at 0.1, 100, 600 and 686 MPa, texture and structure differed significantly from original gels. On the other hand, when all gels were frozen at 200〜400 MPa, the quality of frozen gels improved compared to gels frozen at 0.1 and 100 MPa (ice I). However, quality differed from unfrozen gels. During pressurization exothermic peaks were detected at 0.1, 100, 500〜686 MPa (freezing). However, at 200〜400 MPa, gels did not freeze (supercooling), while after depressurization, the gels froze quickly. Thus, pressure-shift-freezing at 200〜400 MPa was effective in improving the quality of all frozen gels. With the addition of sucrose, the initial freezing temperature decreased. With the increase of sugar, appearance, texture and structure of all gels improved. However, there was no great difference in crystal size among the 5 kinds of sugar (sucrose, glucose, trehalose, solbitol and maltitol).
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