Comparative studies of xanthan, guar and tragacanth gums on stability and rheological properties of fresh and stored ketchup

The effect of three different hydrocolloids (Tragacanth gum, Guar gum, Xanthan gum) was compared on stability, rheological and sensory properties of fresh and 6 months stored tomato ketchup. Gums were added at five levels (0, 0.2, 0.25, 0.3, 0.35 g/100 g (w/w)) respectively to ketchup prepared with starch (0.5 g/100 g (w/w)). Statistical analysis showed gums concentration and type of gums and storage caused a significant effect on rheology and syneresis. According to results, as gums concentration was increased, a decrease occurred in syneresis values and an increase occurred in viscosity, spreadability and yield stress. Xanthan gum created the most overall texture acceptability, structure strength and links strength approximately in both fresh and stored samples in lower concentration than Guar gum and Tragacanth gum. While Xanthan gum or Guar gum created thixotropic behavior, sample containing Tragacanth gum exhibited rheopectic behavior. As concentration of Tragacanth gum was increased, a decrease occurred in rheopectic behavior. In level of 0.25 %, Xanthan gum was better than two other gums in stability, overall texture acceptability, yield stress, structure strength, spreadability, links strength in fresh and stored samples and retaining of thixotropic behavior at the end of storage, while Tragacanth gum created greater viscosity at shear rate of 500 than other two gums in fresh and stored samples that could be related to thermodynamic incompatibility between starch and this gum.