Abstract
Native starch has limitations such as low water solubility and high viscosity. Ozone treatment is a green technique that can be used to modify starch by oxidation without generating waste. Quinoa starch suspensions (10wt%, db) were submitted to the modification process by the application of ozone at different times (OGT = 10, 20 and 30 min), with native starch as the control. Morphological, solubility in water (SW), swelling power (SP) and rheological characterizations were carried out to evaluate the properties of native and oxidized starches. SW values were lower (37.4%) and SP values were slightly lower (6.0%) for native starch and starch modified by 10 min of OGT, when compared to starches with 20 and 30 min of OGT. This indicates a weakening of the bonds in the crystalline region with the longest ozonation times influencing the swelling of the granules and allowing them to absorb water more easily. The rheological tests showed that all samples (5 g gelatinized starch/100 g) had pseudoplastic behavior, with increased pseudoplasticity, consistency index and apparent viscosity, with increasing OGT. The increase in rheological properties after ozone treatment can be attributed to the crosslinking effect. On the other hand, the increase in pseudoplasticity can be explained by the partial depolymerization of amorphous and crystalline lamellae compounds during starch oxidation. Frequency scanning sweep indicated that all samples exhibited weak gel behavior (storage modulus G'>G” loss modulus), without crossing of these moduli. Native starch had the highest G’ and G” values when compared to ozonized starches. No difference was observed in gelatinization temperature and granule morphology after ozone treatment. The differences in the flow and viscoelastic properties can be interesting for different applications, such as thickeners in food or cosmetics products.
