Gelatinization of wheat starch as modified by xanthan gum, guar gum, and cellulose gum.

Cereal Chern. 58(6):513-517 Amylograph curves and Corn Industry Viscometer curves show that guar, xanthan, and carboxy methylcellulose gum hasten the onset of initial paste viscosity and substantially increase final peak viscosity of wheat starch. The early onset of initial viscosity is attributed to detection of the first stage of swelling and is dependent on media viscosity only. Further development of paste consistency can be attributed to interactions of solubilzed starch, gums, and swollen starch granules. Media isolated from starch-guar and starch-xanthan dispersions display synergistic viscosity. Hydrocolloids have been used widely in food products to modify texture, improve moisture retention, control water mobility, and maintain overall product quality during storage (Glicksman 1974). Because wheat starch is a basic ingredient of so many foods, changes in its granule structure and pasting properties in the presence of gums were studied to extend knowledge on the function of starch in cooked and baked products and to expand uses of wheat starch and low-gluten flours in protein-fortified foods (Christianson 1976, Christianson et al 1974). Starch granules, including those from wheat, are composed of linear and branched starch molecules associated by hydrogen bonding either directly or through hydrate bridges. The molecules may form radially oriented crystalline areas or be in amorphorus regions. Micellar networks formed by association of segments of individual molecules in various patterns impart durability to the granular structure and control the swelling behavior of starch during heating. Heating in water weakens the more crystalline network within the granules by disrupting hydrogen bonds with a concurrent loss of anisotropy. In the more amorphous areas, where the molecules are not as closely associated, progressive hydration and swelling occur more rapidly. Molecules of linear amylose are eventually released into solution. Hydrogen-bonding forces in wheat starch granules relax at two different stages of swelling (Leach et al 1959). In the first stage, occurring at 55-70° C, granules swell tangentially and simultaneously lose their characteristic polarization crosses. This initial stage is not normally detectable visco metrically. However. Crossland and Favor (1948) noted that the initial gelatinization stages were observable when wheat starch granules were dispersed in carboxymethyl cellulose (CMC) or alginate solutions. They concluded that the changes in the work required to move the swollen granules past each other are magnified in the more viscous media. Sandstedt and Abbott (1964) have shown similar effects with other cereal starches. An appropriate cause for the large increase in viscosity of wheat starch pastes observed during the second stage of swelling and gelatinization is difficult to assign, even in purely aqueous suspensions. Miller et al (1973) concluded that the increase in viscosity (after most of the granule swelling ceases, 94° C) is due to the released exudate (soluble amylose) and its entanglement with itself, which enhances the viscometric effects. Addition of CMC or alginate could also contribute to this network formation and result in even greater final paste viscosity. Other explanations also need consideration. Purely mechanical