Compositional characterization and rheological properties of an anionic gum from Alyssum homolocarpum seeds

Compositional and rheological properties of Alyssum homolocarpum seed gum, as a new source of thickening agent for application in food industries, were investigated in this study. The extracted gum primarily comprised carbohydrates (61.0 +/- 0.6%), proteins (17.9 +/- 1.0%) and uronic acids (10.9 +/- 0.8%); the main carbohydrates were galactose (65.7%) and rhamnose (18.3%). The polysaccharide backbone was chiefly composed of 1,2-rhamnose, 1,3- and 1,3,6-galactose glycosidic linkages. The average molecular weight of the polymer was 122.5 x 10(6) g mol(-1). Attenuated total reflectance-Fourier transform infrared spectroscopy and zeta-potential measurements revealed that A. homolocarpum seed gum with multiple carboxylic groups was negatively charged in water in the pH range 3-11. Rheological behaviors of the extracted gum were investigated between 0.5 and 5.0% (w/w) concentrations and temperatures of 5 -50 degrees C. Viscosity profile showed shear thinning behavior at all concentrations and temperatures. The pseudoplasticity degree (N) of the extracted polymers increased with concentration while temperature changes did not show any specific trend on N values. The flow activation energy, quantified using an Arrhenius equation decreased from 11.00 to 5.17 (kJ/mol) as shear rate increased, which implied that the aqueous solutions flowed more easily at higher shear rates. The mechanical spectra derived from strain sweep and frequency sweep measurements indicated viscoelastic behavior in all of samples. Frequency sweep data showed that aqueous solutions of gum, displayed weak gel behavior over the range of tested concentrations and temperatures: as dynamic moduli increased with the increased frequency and storage modulus was always greater than loss modulus. Published by Elsevier Ltd.