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S.-T. LIM and M. H. Baek. Graduate School of Biotechnology, Korea Univ., 5-1, Anam-Dong, Sungbuk-Ku, Seoul, 136-701, South Korea The syneresis and related physical changes of a starch gel induced by cold storage or repeated freeze-thawings could be reduced by minor addition of hydrocolloids, but their cryoprotecting mechanism is not fully understood. Although their use as a viscosity enhancer in food system is still common, the cryoprotecting effect draws more concern as frozen food items become popular. The effect depends on the origin and molecular structure of the hydrocolloids, and also on the environmental factors such as pH, ionic strength, and presence of other ingredients. The most frequent visual changes, induced by the cold or frozen storage, include syneresis (water-release) and sponge texture formation. These changes directly relate to the chain associations of amylose and amylopectin, thermodynamically favored under cold storage. Researchers reported the stabilizing effect of hydrocolloids in frozen starch gels was specific to certain starch chains, and the extent depends on the type of hydrocolloids. But the results are still in controversy. Among the many commercial hydrocolloids, alginate, guar, and xanthan were reported highly effective in reducing the syneresis during repeated freeze-thawings. And it was found that there was little relation between pasting viscosity and the syneresis. Recrystallization of amylopectin, measure by thermal analysis, was retarded by the hydrocolloid addition, and its effect depended on the origin of the gum. It was also suggested that the stabilizing effects of the hydrocolloids result from their cooperative interactions towards water as well as starch chains in the gel system.
Session 4, Impact of starch-hydrocolloid interactions in food systems
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