Investigation on structural and physicochemical modifications of standard maize, waxy maize, wheat and potato starches after DIC treatment

This study reports the impact of the Instantaneous Controlled Pressure Drop (DIC®) treatment on structural, thermal and functional properties of starches from four botanical origins (standard and waxy maize, wheat and potato, SMS, WMS, WTS and PTS respectively). The structural and functional properties of treated starches were studied using differential scanning calorimetry (DSC), wide-angle X-ray diffraction, optical microscopy and rheological measurements. For cereal starches the resulting modifications were almost identical: increase of the gelatinization temperature and decrease of the transition temperature range that were ascribed to enhanced stability (or size) and cohesion (or homogeneity) respectively of starch crystallites. Potato starch exhibited the reverse tendency according to its particular structural organisation. All the starches showed a reduction of the gelatinization enthalpy as the intensity of the processing conditions increased. The DIC® treatment seemed to cause total or partial melting of the less stable starch crystallites at low temperatures. As a result, the gelatinization temperatures (To and Tp) of the DIC-treated starches increased; this could be attributed to the melting of the most stable crystallites which needed higher temperature range. Microscopy observations confirmed the partial or total loss of birefringence of treated starch granules. Relative crystallinity decreased upon DIC® treatment with a larger impact on PTS that became amorphous at 2 bar/12 min. The transition for SMS and WTS from A to Vh-type X-ray diffraction pattern revealed the formation of amylose-lipid complexes induced by the treatment. The Brabender viscosity of cereal starches treated at low pressure and processing time was higher than the one of native starches and was clearly reduced for higher pressure levels. For PTS the Brabender viscosity dramatically decreased for all DIC® conditions. Rheological properties of treated starches showed the same tendency except the WTS, whose viscosity was reinforced by the hydrothermal treatment at 3 bar/0.5 min. The study showed that the different responses observed on treated starches were mainly influenced by DIC® processing conditions and by the botanical origin of the starches.