Rheology of Alcayota Gum

M.A. MASUELLI, M. ZANON

Paris

Congreso; 5 World Congress on Biopolymers (Biopolymer Congress 2017); 2017

5 World Congress on Biopolymers (Biopolymer Congress 2017)

Cucurbita ficifolia is a creeping plant with a fleshy fruit, round and elongated, with a thick, smooth shell, resistant to lowtemperatures but not to severe frost (Figure 1). The mesocarp (pulp) is white with a granular and fibrous texture. Thefruit was separated into three parts: peel, pulp and seeds. The pulp was dried and then ground to obtain the flour from whichthe hydrolysis was carried out. Hot aqueous extracts were made to the moist pulp and a Cy (d) dispersed (used for rheology)solution Cy (d) solution (used for capillary viscosimetry) was obtained. From Cy concentrations of 0.1%, 0.2%, 0.4% and 0.6%wt. in an aqueous solution of 0.1M NaCl, which acts as a stabilizer, the intrinsic viscosity was measured with an Ubbelodhe 1Bviscometer and density with Anton Paar DM35N densimeter in the thermostatic bath at 25°C. The hydrolysis procedure wasperformed on the Cy (d) dispersion, with 0.1M NaOH at 65°C for two hours and then precipitated with ethanol. The precipitateis washed with ethanol several times, obtaining a polysaccharide of average molecular weight having free oxydril groups calledCyOH (d). To the above dispersion (CyOH (d)) was added 5 ml of glycerol and stirred cold for a few minutes to homogenize,these solutions were used to measure the flow ability curve. Also, dispersions of Cy (d) of different concentrations: 2, 3, 4, 5, and6% in distilled water were prepared. Some of them were hydrolyzed, being named as CyOH (d) and measured with a BrookfieldDVIII rheometer at a temperature of 25°C. The assay was repeated by adding 2, 4 and 5% glycerol to some of the hydrolyzeddispersions at temperatures of 35 and 40°C in a thermostatic bath. The intrinsic viscosity was 149.83 cm3/g and the molecularweight was 1867000 g/mol (Marck-Houwink parameters of k = 0.00263 and a= 0.7583), with a hydrodynamic radius of 53nm,a shape factor of 3.12 and a hydration value of 47.63 g/g. Studies for CyOH (d) showed a thixotropic behavior for dispersedsolutions which increased with increasing hydrolysis and glycerin and decreased with increasing temperature. The degree ofthixotropy is higher for CyOH (d) compared to Cy (d).