COMPLEXATION INDUCED CHANGES OF RHEOLOGICAL PROPERTIES OF STARCH SYSTEMS AT DIFFERENT MOISTURE LEVELS

Starch, especially the linear amylose fraction, is able to form helica l inclusion compounds or complexes with molecules like flavor compound s, fatty acids, and emulsifiers. The effects of starch complexation on theological properties were studied (a) in aqueous dispersions of 1%- 4% starch content, (b) in high-concentration gels of 40% starch conten t, and (c) in extrusion cooked low moisture starch blends. Complexatio n was followed by iodine binding capacity of starch and by differentia l scanning calorimetry. Rheological characterization was based on dyna mic and steady shear measurements and on uniaxial force deformation te sts. At low starch concentrations, the addition of complexing emulsifi ers and flavor compounds induced gelation, provided that enough amylos e was solubilized and swollen granules were present. Likewise, freshly prepared high-concentration starch gels with the addition of complexi ng ligands exhibited higher moduli of deformability than control sampl es without additives. The sequence of moduli of elasticity became inve rse during storage as complexation lowered the rate of amylose retrogr adation. Melt viscosity during cooking extrusion increased with the ad dition of both complexing emulsifiers and noncomplexing triglycerides, while paste viscosity of ground extrudates increased with emulsifiers but not with triglycerides. Influence of starch complexation seems to be parallel for all moisture levels indicating that the main feature is the formation of insoluble amylose complexes which in turn lead to the formation of a firmer network between the dispersed starch granule s. (C) 1995 Society of Rheology.