• The Korean Journal of Food And Nutrition
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• v.10 no.2
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• pp.228-233
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• 1997

The effects of spray drying and extrusion drying on functional properties of agar were investigated to increase the availability of agar in food industry. In case of unmodified and spray-dried agar, gel strength and viscosity were 1,070g/$ extrm{cm}^2$ and 170.50pcs, 820g/$\textrm{cm}^2$ and 17.07cps, respectively, while 523.28g/$\textrm{cm}^2$ and 12.81 in extrusion-dried product. The lowest dissolving onset and conclusion temperature were revealed in extrusion sample, where it was attained in 80 and 11$0^{\circ}C$ of unmodified, 60 and 9$0^{\circ}C$ of spray-dried, and 35 and 8$0^{\circ}C$ of extrusion-dried agar, respectively. Melting and setting in unmodified sample were showed to 110.17 and 40.52, 90.05 and 39.54$^{\circ}C$ in spray dried, and 80.01 and 36.05$^{\circ}C$ in extrusion-dried agar, respectively.

• The Korean Journal of Food And Nutrition
• /
• v.10 no.2
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• pp.234-240
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• 1997

Agar has widely been used as medical aids and food ingredients due to its pecular physicochemical and rheological properties. In this paper, the effects of spray drying and extrusion drying on functional properties of agar were investigated to clarify the sol-gel transition mechanism at low temperature and microstructure of agar gel by measuring phase transition by differential scanning calorimetery, structural differences by light microscope and scanning electron microscope observation. The lowest endothermic onset(To), peak(Tp), conclusion(Tc) temperature and enthalpy($\Delta$H) using differential scanning calorimetery were showed in extrusion-dried agar wic were checked in 41.30, 61.72, 80.50 and 0.73cal/g. In cases of unmodified and spray-dried, the values were 81.20, 95.51, 112.14 and 3.22cal/g, and 60.11, 76.45, 89.54 and 1.53cal/g, respectively. When all samples were reheated using differential scanning calorimetery after gelling fully, no significant differences of endothermic To, Tp, Tc and $\Delta$H appeared. The surface structure of unmodified agar powder observed by light microscope and scanning electron microscope appeared a continuous surface without any indication of small pores, gaps or point of discontinuity. In cases of spray-dried agar, the unstable structures with pores was resulted. The microstructures of extrusion-dried agar, however, was solid with large gaps and areas of discontinuity in the surface. From the results above, it was suggested that significant differences in phase transition and surface microstructures were clearly related to the physicochemical changes and rheological properties, solubility and gelling ability of the types of agar gel.