Effect of S. macrosiphon and L. perfoliatum seed gums on rheological characterization of bitter orange (Citrus aurantium L.) and pomegranate (Punica granatum L.) paste blends.

The steady shear flow properties of bitter orange and pomegranate pastes and blend of two pastes including 0.5% Salvia macrosiphon (SMG) and L. perfoliatum (LPG) seed gums, two traditional Iranian hydrocolloids, were determined. All treatments exhibited shear-thinning behaviour. LPG added sample showed stronger shear thinning behaviour than the other due to its high molecular weight and intermolecular through hydrogen bonds and polymer entanglement. Ostwald model was found the best model to describe steady shear flow behaviour among different time-independent rheological model applied. Treatments including 0.5% these two seed gums indicated a flow behaviour index less than 0.6 and consistency coefficient raised by increasing concentration from 60 °Bx to 76 °Bx in bitter orange paste (from 0.55 Pa s(n) to 32.58 Pa s(n)), pomegranate paste (from 0.55 Pa s(n) to 84.87 Pa s(n)) and mix of these two pastes (from 0.64 Pa s(n) to 56.9 Pa s(n)). Oscillatory shear data showed weak gel-like behaviour of bitter orange and pomegranate pastes treatments including seed gums with the elastic modulus predominating over the viscous one at lower frequency. However, after weak gel formation, G″ was higher than G' in the frequency range of 0.01 to 10 Hz. An Ostwald model was used to describe the changes of viscose modulus with frequency. The results indicate that the elastic properties of bitter orange/ pomegranate paste and bitter orange paste may be increased by the presence of LPG and SMG due to associations of ordered chain segments of these gums, resulting in a weak three-dimensional network.