Effects of xyloglucan on the gelatinization and retrogradation of corn starch as studied by rheology and differential scanning calorimetry

Effects of xyloglucan (XG) on gelatinization and retrogradation of corn sta rch (CS) were studied as a function of mixing ratio and of storage time and by measuring force-deformation curves, dynamic viscoelasticity, syneresis and differential scanning calorimetry (DSC). Total polysaccharide concentra tions were 3.5 wt% or 20 wt% and CS/XG mixing ratios were 10/0, 9.5/0.5, 9. 0/1.0 and 8.5/1.5. Results of dynamic viscoelasticity and DSC measurements indicated that XG did not interact synergistically with CS to promote the f ormation of three dimensional network structure of CS. The storage and loss Young's moduli, E' and E " for mixed gels of CS and XG increased with incr easing XG concentration. E' and E " decreased with increasing temperature f rom 25 degrees C-60 degrees C, and increased slightly with decreasing tempe rature from 60 degrees C-25 degrees C, E' and E " did not recover the initi al value at 25 degrees C when the temperature was lowered from 60 degrees C -25 degrees C. E' and E " at 25 degrees C increased with increasing storage time, while both moduli at 25 degrees C after heating-cooling cycle were n ot so different for gels after 1 day storage and for gels after 7 or 14 day s storage. Breaking stress and Young's modulus for gels increased, while br eaking strain decreased with storage time, Breaking stress and retrogradati on ratio by DSC for mixed gels with mixing ratio CS/XG = 8.5/1.5 proceeded faster during 7 days of storage and proceeded slower after 7 days storage t han gels of corn starch (10/0). (C) 1999 Elsevier Science Ltd. All rights r eserved.