Gel formation in mixtures of hydrophobically modified potato and high amylopectin potato starch

The rheological properties of gels of hydrophobically modified potato starch (HMPot) and high amylopectin potato starch (HAPP) were studied by small deformation oscillatory rheometry. The hydrophobic modification consisted of octenyl succinate anhydride (OSA) chains grafted mainly on the amylopectin molecules. The rheological behaviour of HMPot was different from the behaviour of native potato starch and HAPP. At concentrations higher than ∼15%, the moduli for HMPot starch were higher than for native potato starch and HAPP. A higher level of OSA Substitution led to lower moduli values. The gel formation of HMPot was slower than the gel formation of native potato starch and HAPP. This was explained by the formation of amylose–OSA inclusion complexes and OSA–OSA hydrophobic interactions. Decreasing concentrations of HMPot in HMPot–HAPP mixtures led to reduced moduli values, and a rheological behaviour resembling that of HAPP. At HMPot concentrations lower than 50% in the HMpot–HAPP mixture, amylose or OSA seemed not to contribute to the network formation. Addition of sodium dodecyl sulphate (SDS) to HMPot reduced the moduli at lower concentrations (1%). Further increase in SDS concentration (2%) increased the moduli values. However, the moduli values were still lower than for pure HMPot. The decrease in the moduli when SDS was added is Suggested to be due to a replacement of OSA by SDS in the amylose–inclusion complex. The strengthening of the existing OSA–OSA hydrophobic interaction when further SDS was added, is explained by the formation of polymer-micelles. When SDS was added to native potato starch and HAPP the rheological behaviour was different from that observed for HMPot starch. The moduli increased when SDS was added to native potato starch and HAPP. With increasing SDS concentration, the storage modulus (G′) of native potato starch and HAPP increased to the same value. Consequently, the rheological properties of native potato starch and HAPP were suggested to be dominated by amylopectin and not by amylose.