Study of DIC hydrothermal treatment effect on rheological properties of standard maize (SMS), waxy maize (WMS), wheat (WTS) and potato (PTS) starches

International audienceStandard maize (SMS), waxy maize (WMS), wheat (WTS) and potato (PTS) starches were hydrothermally treated by Instantaneous Controlled Pressure Drop (DIC) process at different pressure levels (1, 2 and 3 bar) corresponding to the temperatures of 100, 122 and 136 C, respectively. The rheological properties and particle size of treated starches under various conditions were compared to the native ones. The results showed for all starches, except for WTS, a reduction of the consistency coefficient and the yield stress (s0) with increased intensity of the hydrothermal treatment conditions. Furthermore, s0 vanished for severe treatment conditions. The DIC treatment yielded an increased fluidity and a loss of the conservative modulus of the pastes, as a result of partial gelatinization of starch granules. The extent of the observed effect depended on the botanical origin. Wheat starch exhibited a different behaviour: the consistency coefficient and the conservative modulus being higher for DIC treated starch except for the most severe conditions

Structural modifications and thermal transitions of standard maize starch after DIC hydrothermal treatment

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

Investigation on the Emission of Volatile Organic Compounds from Heated Vegetation and Their Potential to Cause an Accelerating Forest Fire

International audienceAn experimental study is conducted on the emission of volatile organic compounds (VOCs) emitted by Rosmarinus officinalis plants when exposed to an external radiant flux. The thermal radiation heats the plant and causes the emission of VOCs. The thermal radiation simulates the radiant flux received by vegetation in a forest fire. The results of the experiments are used in a simplified analysis to determine if the emissions of VOCs in an actual forest fire situation could produce a flammable gas mixture and potentially lead to the onset of an accelerating forest fire. The experiments consist of placing a plant in a hermetic enclosure and heating it with a radiant panel. The VOCs produced are collected and analyzed with an automatic thermal desorber coupled with a gas chromatograph/mass spectrometer (ATD-GC/MS). The effects of the fire intensity (radiant panel heat flux) and the fire retardant on the VOCs emission are then investigated. Two thresholds of the VOCs emission are observed. The first is for plant temperatures of around 120C and appears to be caused by the evaporation of the water in the plant, which carries with it a certain amount of VOCs. The second one is around 175C, which is due to the vaporization of the major parts of VOCs. The application of a fire retardant increases the emission of VOCs due to the presence of the water (80%) in the fire retardant. However, the use of the retardant results in a lower production of VOCs than using water alone. The measurements are used to estimate the concentration of VOCs potentially produced during the propagation of a specific fire and compared to the flammability limits of a-pinene. It is concluded that the quantities of VOCs emitted by Rosmarinus officinalis shrubs under certain fire conditions are capable of creating an accelerating forest fir

EFFECT OF INSTANTANEOUS CONTROLLED PRESSURE DROP TREATMENT (DIC) ON THE SORPTION ISOTHERMS OF STANDARD MAIZE, WAXY MAIZE, AND POTATO STARCHES

International audienceWe applied The Instantaneous Controlled Pressure Drop process (DIC) for starch heat treatment in order to modify its functional and structural properties. The effect of DIC treatment on the sorption capacity was studied for standard maize (SMS), waxy maize (WMS) and potato (PTS) starches,. The isotherms for native and DIC treated starch were determined at 25°C using a standard gravimetric technique. The isotherm curves obtained have a sigmoidal form; exhibiting behaviour of Type II. The sorption isotherms of DIC treated starches are even below to the sorption isotherms of native starches, and the sorption capacity decreased with increasing processing pressure. The isotherms were analysed according to GAB equation, which distinguish between different physical forms of moisture distribution. The GAB model gave the best fit to the experimental data. W0 values of the mono-layer moisture content for all three starches decreased with an increase of severity of DIC treatment

Effect of DIC hydrothermal treatment on gelatinization and retrogradation properties of standard maize, wheat and potato starches.

International audienceThe gelatinization and retrogradation of DIC hydrotreated starches with different processing conditions and native starches were studied by differential scanning calorimetry (DSC). Standard maize (SMS), wheat (WS) and potato (PS) starches were hydrothermally treated at residual moisture content (~12% wb) by Instantaneous Controlled Pressure Drop for various pressure levels (1, 2 and 3 bar) and processing times. The temperatures of gelatinization (T0, Tp) increased with increasing conditions of DIC treatment for SMS and WS starches, whereas they decreased for PS. These temperatures shifted for SMS, respectively, from 63.1-69.6 °C (native) to 70.7-75.5 °C (treated at 2 bar/30 min), for WS from 50.4-56.6 °C (native) to 59.9-64.4 °C (treated at 2 bar/1 0min) and for PS from 57.7-61.6 °C (native) to 49.1-58.0 °C (2bar/2min). The endothermic gelatinization enthalpy decreased with the severity of DIC treatment and the retrogradation enthalpy increased faster for DIC treated starches than for untreated starches

Effect of instantaneous controlled pressure drop (DIC) on physicochemical properties of wheat, waxy and standard maize starches

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