Effects of food gums on viscosities of starch suspensions during pasting

Pasting curves of starches in gum (hydrocolloid) solutions at low concentrations (starch 3.6%, gum 0.4%) were produced with a Brookfield viscometer. Gums produced a variety of effects on viscosities of starches during starch pasting (increase or decrease greatly or slightly or no effect). A viscosity increase before the normal starch pasting temperature was detected for normal maize starch in the presence of carboxymethylcellulose (CMC), gellan, xanthan, guar gum, and sodium alginate. Waxy maize, waxy rice, tapioca, regular rice, potato, and wheat starches gave mixed responses. It appeared that interactions between certain leached molecules, primarily amyloses, and certain gums were responsible for the viscosity increase occurring before starch pasting. The pasting peak viscosity of potato starch was greatly decreased by negatively charged gums (CMC, carageenans, alginate, xanthan). The repelling forces between the phosphate groups on potato starch and the negative charges on molecules of these gums were hypothesized to be the cause. This hypothesis was supported by results from similar systems (potato starch plus salt solution and phosphorylated normal maize starch plus anionic gums), both of which systems also produced lower peak viscosities. It was found, by microscopic examination of potato starch heated to 95 °C in solutions of ionic gums without shear, that the gums altered the granule pasting process.