Rheological and thermal characterization of Okenia hypogaea (Schlech. & Cham.) starch

The objective of this work was to characterize the thermal and rheological properties of okenia (Okenia hypogaea) starch compared with those of a commercial one (corn). Chemical analysis, differential scanning calorimetry, viscoamylography, swelling and solubility, viscometry and oscillatory dynamic tests were applied to starch samples with 5 and 10% (w/v) of total solids. The chemical analysis indicated that okenia starch could be classified as ‘normal’. The thermal analysis showed that okenia starch had a gelatinization temperature (71.3 °C) significantly smaller (α=0.05), than that of corn starch (73 °C). The melting temperature of okenia starch presented a significant increase starting from the 7th day of storage, but from the 14th day onwards, this was constant, while for corn starch it increased until the end of the storage period. Overall, okenia starch presented higher values of swelling capacity than corn starch while for the solubility, the opposite effect was observed. The amylograms of the starch pastes showed higher maximum viscosity for okenia starch, as well as a smaller tendency to the molecular dissociation and re-association than for corn starch. The flow curves showed for both starches a non-Newtonian behavior, the samples with 5% (w/v) of solids exhibiting thixotropy. The dynamic tests showed that both Okenia and corn starch dispersions presented changes in their rheological properties when the temperature increased, going from a highly viscous system (loss modulus, G″ predominating), to a mainly elastic one (storage modulus, G′ predominating), both starches forming weak viscoelastic gels.