INFLUENCE OF LIPIDS ON THE THERMAL AND MECHANICAL-PROPERTIES OF CONCENTRATED STARCH GELS

Interactions between lipids [sodium dodecyl sulfate (SDS); glycerol monostearate; cetyltrimethylammonium bromide; L-alpha-lysophosphatidylcholine (LPC)] and starches (wheat, rice, pea, and garbanzo bean) were studied in thermoset gel networks of high starch concentrations (20-35% w/w) by small amplitude oscillatory shear measurements and differential scanning calorimetry. All lipids reduced the apparent gelatinization enthalpies of the granular starches, suggesting complexation with the starch molecules upon heating; granule structure destabilization effects were shown only with SDS. Although rice and wheat starch gels exhibited higher storage modulus (G') values when lipids were included, smaller changes in the viscoelastic properties were observed for the legume starches; the higher amylose content of pea and garbanzo bean starches appears to dominate the rheological behavior of their composite gels. Among the lipids examined, LPC exerted the greatest effect in increasing the G' and decreasing the tan delta (G"/G') of rice and wheat starch gels. Kinetic experiments on the evolution of modulus (G') and the development of the staling endotherm during storage of gels (35% w/w, 8-degrees-C) indicated that lipids retard both processes. At concentrations between 8 and 40% (w/w) of rice and garbanzo bean starch gels, the dependence of storage modulus on starch concentration (C) followed power law relationships; G' varied as C2.1-2.9.