Freeze–thaw stabilization of sweet potato starch gel by polysaccharide gums

Nine polysaccharide gums (sodium alginate, carboxymethyl cellulose, curdlan, gellan, guar gum, gum arabic, κ-carrageenan, locust bean, and xanthan) were compared for their stabilizing effects in sweet potato starch gel against repeated freeze–thawing (FT) treatments. The gums were added in starch gel at 0.3 or 0.6% (w/w, based on total gel weight), and total solid content in the gel was adjusted to 7% (w/w) with starch. The gels containing starch and gum were repeatedly freeze–thawed up to five times by storing at −18 °C for 20 h and then at 25 °C for 4 h. Water release (syneresis) was measured by vacuum-filtering the freeze–thawed gels. Among the gums tested, alginate, guar gum, and xanthan were highly effective in reducing the syneresis. For example, guar gum, at 0.6%, showed the least syneresis (33.0%, w/w based on initial water content) after five FT cycles, which was less than half that of pure starch gel. At 0.3%, however, xanthan was more effective than guar gum in reducing syneresis. Xanthan reduced paste viscosity significantly, whereas guar gum and alginate increased the viscosity, but there was little relation between pasting viscosity and syneresis. The gums remained in the gel matrix during the syneresis without a significant loss. Recrystallization of starch (retrogradation) induced by FT treatment was also retarded by the presence of gums, and sodium alginate was more effective in retarding the retrogradation than xanthan or guar gum.