Textural Change of Freeze-dried Agar and Gelatin in the Presence of Ice Crystral-controlling Proteins

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We examined the textural changes such as hardness, porosity, and water absorbency of freeze-dried agar and gelatin using the ice nucleation active bacterium, Xanthomonas campestris pv. translucens NBRC 13559 cells as the heterogeneous ice nuclei and antifreeze proteins (AFPs) . NBRC 13559 cells could easily freeze their hydrogels without supercooling. The hardness of their freeze-dried products using NBRC 13559 cells was less than that using X. campestris NBRC 13551, which dose not possess any ice nucleation activity, and that without the additions. On the other hand, the hardness of their freeze-dried products using AFPs was more than that without the additions. When AFPIII (type III), one of AFPs, was used for only agar, their pore sizes were smaller than those without the additions, thereby decreasing their water absorbencies. When antifreeze glycoprotein (AFGP) was used for only gelatin, their pore sizes and water absorbencies were similar to that of AFPIII used for the agar. As the pore sizes of the freeze-dried agar using the NBRC 13559 cells were larger than those using the NBRC13551 cells and without the additions, the water absorbency of the freeze-dried agar using the NBRC 13559 cells increased. This report contains the first comparison of the ice nucleation and antifreeze activities for the textures of freeze-dried gelatin and agar.
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