International audienceStandard maize starch was hydrothermally treated by Instantaneous Controlled Pressure Drop (DIC) process at three pressure levels (1, 2 and 3 bar) corresponding to the temperatures of 100, 122 and 135 C (at 13–27% moisture), respectively. The structural effects of various hydrothermal conditions were examined with differential scanning calorimetry (DSC) and wide-angle X-ray diffraction. In order to understand the changes that occur during DIC treatment, melting endotherms of native maize starch at various moisture contents were determined. The gelatinization temperatures of DIC treated standard maize starch increased with DIC treatment. The transition temperatures (To, Tp) are closely related to the combined effect of pressure and processing time. At approximately 10 min of processing time, To and Tp were 65.7 and 72.3, 68.8 and 73.6 C, 74.8 and 79.8 C for pressure levels of 1, 2 and 3 bar, respectively (against 63.1 and 69.6 C for native starch). DIC treatment narrowed the gelatinization temperature range and decreased gelatinization enthalpy (DH), as the severity of processing conditions increased. DH decreased from 11.4 J g1 (native) to 11.0 (1 bar), 9.0 (2 bar) and 1.7 J g1 (3 bar) for treated maize starch during approximately 10 min. Relative crystallinity of hydrothermally treated starch decreased with increasing DIC conditions. The A-type crystalline pattern was progressively lost (at pressure level P2 bar) and substituted by the Vh-type X-ray diffraction pattern, corresponding to the formation of amylose–lipid complexes. For severe DIC conditions (pressure level of 3 bar), the substitution was completed. Microscopic observations revealed progressive loss of the birefringence of DIC treated starch granules except at low pressure (1 bar), while the integrity of starch granules was preserved for all the conditions. These modifications that reveal important changes in the crystalline organization of the starch granules are related to their functional properties

Standard maize starch was hydrothermally treated at residual moisture content (~12 %) by Instantaneous Controlled Pressure Drop for various pressure levels and processing times. In order to examine the homogeneity of the starch treatment, three thicknesses (1.5, 1 and 0.5 cm) were tested at 3 bar of steam pressure. For the three thicknesses, the temperature and the moisture content of starch were measured during the treatment at the bottom and the surface.The results showed an absence of gradient of temperature and moisture content only for a thickness of 0.5 cm. Gelatinization transition temperatures (T o , T p ) increased after hydrothermal modifications. The change in the gelatinization temperature range was observed after DIC treatment when pressure level or processing time increased. For a high pressure (≥ 4 bar) associated with low processing time (2 minutes) a total gelatinization of starch was observed. It also occurs when the processing time is important (~15 min) and pressure lower than 4 bar.

International audienceStandard maize starch (SMS), waxy maize starch (WMS) and wheat starch (WTS) were hydrothermally treated by the Instantaneous Controlled Pressure Drop (DIC) process. This process consists in a short pressurisation obtained by the injection of saturated steam at fixed pressure during a predetermined time followed by a sudden pressure drop towards vacuum. The effects of DIC conditions on thermal characteristics, enzyme susceptibility, pasting (Brabender) and rheological properties of treated starches were investigated. For treated starches, an increase of transition temperatures (To and Tp), a narrowing of the width of gelatinization endotherms and a decrease of the gelatinization enthalpies (DH) were observed as the severity of processing conditions increased. WMS, SMS and WTS showed a significant increase in enzymatic hydrolysis after treatment. The saccharification yield showed an increase from 19% (native) to 44%, 21% (native) to 59% and 55% (native) to 79% for SMS, WMS and WTS, respectively. The study suggests that the structural modifications due to the previous DIC treatment influence the in-vitro hydrolysis and the access to the ultrastructure of starch granules; the susceptibility to hydrolysis increases from SMS to WMS and WTS. For all treated starches, the decrease in peak viscosity and in apparent viscosity was related to the processing conditions

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International audienceInstantaneous Controlled Pressure Drop, ‘De´tente Instantanée Controˆlée' (DIC) was performed on standard maize starch at residual moisture content (~12%). Changes in moisture distribution were observed during the treatment and modelled through a phenomenological model based on gravimetric data. The model proposes an exponential variation in the moisture content with processing time at various pressures. The predicted data were found to be in good agreement with experimental data. The values of water activity coefficient (c) obtained from the model decrease, when processing pressure increases; 5.86, 3.71 and 3.36 (dry basis))1 for 1, 2 and 3 bar, respectively. The mass transfer coefficient decreases, when the pressure increases. Its value ranged from 5.89 · 10)5 m s)1 for 1 bar down to 0.92 · 10)5 m s)1 for 2 bar and 0.77 · 10)5 m s)1 for 3 bar. This coefficient is not only controlled by a simple resistance to the mass transfer, but also by gelatinisation phenomenon that progresses when temperature increases