Neutral hydrocolloids promote shear-induced elasticity and gel strength of gelatinized waxy potato starch

Shear forces are important during food processing, food consumption, and food digestion, and often are estimated to evaluate their effects on product quality. However, few studies have been done on shear-induced structure changes of starch/hydrocolloid systems. Our previous work showed that gelatinized waxy potato starch forms a strong viscoelastic gel under the application of long-term low shear at low temperatures, a phenomenon that is not noted in other waxy starches such as rice and corn. In the present study, the rheological properties of gelatinized waxy potato starch in the presence of neutral (guar gum and konjac glucomannan) and anionic hydrocolloids (gum arabic, xanthan gum, sodium alginate, and pectin) were investigated. Results showed that gelatinized starch dispersions containing hydrocolloids with flexible polymer chains (guar gum, konjac glucomannan, sodium alginate, and pectin) or a highly-branched structure (gum arabic) were able to produce gels with a more liquid-like behaviour when compared to gels produced by dispersions containing hydrocolloids with rigid chains (i.e., xanthan gum). Phase separation in starch/xanthan gum system and formation of a 3D-network in the xanthan gum phase may be responsible for the strengthened gel structure resulting in high elasticity. When shearing the gelatinized waxy potato starch/hydrocolloid dispersions at 5 degrees C for 24 h at 20 s(-1), the presence of neutral and highly viscous hydrocolloids drastically increased the gel strength, while anionic and low viscous hydrocolloids decreased it. Such decrease in gel strength was attributed to the electrostatic repulsion between anionic hydrocolloids and the naturally negatively charged phosphorylated chains of waxy potato starch.