Textural and rheological observation of the synergistically interacted salep glucomannan- xanthan gum gels

The aim of this thesis is the investigation of hydrocolloid ratio effect (3SK, SK and 3KS) on gelation properties of salep glukomannan (S) and xanthan gum (K) based on various pH values (water, pH 5.5 and pH 4.0) which exhibited strong gel behavior due to their synergistically interaction. The rheological analysis that performed to reveal viscoelastic behavior have been composed of following analyses: temperature sweep test for determining of sol-gel transition temperature namely gelling point, stress sweep test, frequency sweep test, temperature sweep for determining of gel-sol transition temperature namely melting point and creep-recovery tests. The gelation temperature was rate-independent in varied environments, but the sol-gel transition temperature determined in water and at a pH of 5.5 decreased from 58 to 53 °C when the pH was 4.0. The early structural development of highly concentrated xanthan (SK and 3KS) solutions was observed during the cooling process in temperature sweep test. In the gelled samples, 3KS and SK had more linear viscoelastic regions and higher yield stress values than 3SK when more stress was applied and the pH decreased. The gel was strong at a low frequency but weak at a high frequency. The early transition frequency of these gel types was observed for 3SK at low pH values, indicating that it had fewer junction points, and the average size of the junction points in the gel network were lower. The melting temperatures of the gels which showed the thermo-reversible behavior was determined to be higher for 3KS due to the stronger and more abundant junction zones. Thus, 3KS had a higher thermal stability than SK and 3SK. Other data supporting this result were observed by determining the creep-recovery parameters, color and gel strength values of texture analysis. The synergistically interacting salep-xanthan gels were shown by FTIR and these gels exhibited high water holding capacities. The usage of the same proportion of polymers (SK) and high salep ratios (3SK) seems more preferable in the water system, while higher xanthan ratios (3KS) were needed at low pH values if better a gel behavior was desired, such as for the potential use of these materials in food and biomedical applications.