Influence of pH and salt on the rheological properties of dispersions prepared from the galactomannans extracted from Gleditsia triacanthos seeds

BARRERA GABRIELA NOEL; MOLDENAERS PAULA; FORMENTI SUSANNA ; LAURA ITURRIAGA; RIBOTTA PABLO DANIEL

Zurich

Simposio; ISFRS 2019 - International Symposium on Food Rheology and Structure; 2019

Institute of Food, Nutrition and Health at ETH Zürich

The exploration of new renewable sources and non-traditional sources of hydrocolloids as alternative to traditional additives products has increased in the last years. The gum presence in the Gleditsia Triacanthos (Leguminosae) seeds has been reported1. Gleditsia Triacanthos (Gledi) is a woody species that blooms in the southern hemisphere. Gledi is widely spread in Argentina, especially in Córdoba2, and the wide variety of resources offered by this species has not been exploited yet. Regarding Gledi studies, researchers3 have concluded that the fraction of galactomannans extracted with hot water treatment could be a potential additive in food industry. The objective of this work was to study the effect of pH and salt on the rheological properties of dispersions prepared from the galactomannans extracted from Gledi seeds. The yellowish-powder obtained from the extraction of Gledi milled-seeds with hot-water and ethanolic precipitation was dispersed (stirring: 30min at 25°C+1h at 90°C) in water (Gledi-H2O) and in aqueous solution of NaOH (5x10-6M; pH=8) (Gledi-NaOH), HCl (1x10-4M; pH=4) (Gledi-HCl) and NaCl (0.4M) (Gledi-NaCl) to obtain samples at 2%w/w. The pHs and salt concentration were chosen considering the values typically found in food matrices. The systems structure was evaluated by Frequency-sweeps, Capillary breakup extensional rheometry and Thixotropy oscillation test (3ITT). The samples showed a concentrated macromolecular-solution behavior with viscoelastic-fluid behavior at low frequencies and viscoelastic-solid behavior at high frequencies. The cross-point frequency decreased and characteristic relaxation time increased as a consequence of lower pH and salt presence. Gledi-H2O dispersion showed the lowest G´´ and G´ moduli. These results suggested the formation of a more entangled polymer network as a consequence of the chemical-environment changes of the galactomannans aqueous-dispersions. The apparent extensional viscosity and relaxation time of Gledi-HCl and Gledi-NaCl samples were higher than the others dispersions, probably due to an increase of the chains-entanglement density which could be suggesting the development of a larger network structure. On the other hand, Gledi-NaCl sample exhibited the most deformation tendency and the longer time to recover it is structure at the measurement conditions. Gledi-NaCl dispersion structure was more sensitive to high shear rate deformation.