Other physical modifications retrogradation

When starch granules are cooked in a food process, the crystalline structure is lost and amylose and amylopectin are dispersed to a certain extent (gelatinization). The extent depends on water content, temperature, time, and degree of shear of the process. To produce low-GI foods in this situation, physical modification (i.e. starch concentration, processing condition, and storage method) can be used to moderate starch digestion properties. Modification of starch gelatinization and retrogradation are the main categories of physical modification used to achieve low-GI benefits in cooked and processed starchy foods.

As described above, native starch (especially A-type) is an ideal SDS, and, if incomplete gelatinization can be achieved through lowering temperature, decreasing water content, or shortening processing time, the nutri tional benefits of SDS will be partially retained. However, the organoleptic properties may not be suitable for consumption. This means that improved food processing technologies are needed to impart low glycemic properties. Hydrothermal modifications of the nutritional properties of starch could conceivably also be applied in food processing to achieve a low-glycemic food product.

Extensive research has shown that water content, temperature of storage, and the existence of other ingredients affect starch retrogradation. Most of the RS in food is produced through retrogradation, particularly by amylose retrogradation which occurs very rapidly. Thus, foods produced with high-amylose starch usually have low GI values due to the occurrence of retrogradation. Alternatively, low-GI or controlled glycemic foods can also be made using SDS ingredients. Preliminary data from our laboratory (G. Zhang and B. R. Hamaker, unpublished data, 2005) show that controlled retrogradation can be used to make SDS. Similarly, Shi et al. (2003) and Shin et al. (2004a) showed that less retrogradation with partially debranched starch ingredients makes it possible to produce SDS. Perhaps SDS, in these cases, is due to the formation of imperfect crystallites.

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