Effet de traitements physiques (Homogénéisation à Basses Pressions et Détente Instantanée Contrôlée (DIC)), sur les propriétés physico-chimiques, structurales et fonctionnelles de la farine de riz et aptitude à la panification de formules sans gluten.

Abstract

Our present thesis aimed to study in gluten-free (GF) breadmaking on the one hand the effect of Low Pressures Homogenization (LPH) treatment on the physico-chemical and functional properties of two rice flour varieties (long rice flour (LRF) and medium rice flour (MRF)) and on the other hand, the effect of Instant Controlled Pressure Drop treatment (DIC) on the technological properties of a glutenfree formula (GFF) based on rice and faba bean (RFF). In the first part of this work, the impact of LPH (30, 50 MPa and 1, 2, 3 passes) on the physicochemical and functional properties of LRF and MRF (particle size distribution (PSD), bulk density (BD), hydration properties, oil absorption capacity (OAC), thiol groups content, emulsifying properties and surface hydrophobicity) was evaluated. In the same part, the microstructure of selected samples (30, 50 MPa and 3 passages) were characterized, added to amylose content, crystal structure by X-Ray Diffraction (XRD) analysis, molecular structure by FTIR spectroscopy, pasting and thermal properties. In the second part, the effect of LPH (30 MPa and 3 passes) on the technological quality of GFB without additives was evaluated (the baking weight loss, the final moisture content, color, texture and crumb alveolar structure (image analysis) and the staling properties of GFB. In the third part which concerns the DIC, the Response Surface Methodology (RSM) was used through a central composite experimental design (CCD) with two factors, (X1 Temperature (from 100 to 165°C)/the dry saturated steam pressure (from 0.1 to 0.7 MPa) and X2 treatment time (from 20 to 60 s) to study and optimize the effect of DIC on the technological quality of GFB (Specific volume (Vsp) and crumb alveolar structure). The results of the first part showed that LPH (30, 50 MPa and 1, 2 and 3 passages) caused a critical PSD reduction of LRF and MRF. A strong correlation was noted between this PSD reduction of LRF and MRF and their physicochemical properties changes. LPH significantly decreased the BD and the emulsion stability of LRF and MRF and increased the water absorption capacity and swelling volume of LRF in addition to the emulsifying activity of MRF. On the other hand, the OAC, the thiol groups content and the surface hydrophobicity of LRF and MRF were significantly increased by LPH. The microstructure of selected LRF and MRF samples (30, 50 MPa and 3 passes) was affected by LPH, but without modifying the XRD pattern and the starch crystallinity. The FTIR spectra suggested the modification in RF constituents structure, particularly for MRF. The pasting and thermal properties for both RF varieties (LRF and MRF) were significantly affected by LPH. A principal component analysis (PCA) showed discrimination of RF samples according to the variety and the level of pressure applied. In the second part conserns the GF breadmaking, LPH (30 MPa- 3 passes) increased the RFs damaged starch content, thus leading to higher expansion volumes during GFB batters’ fermentation. In addition, this treatment modified the crumb color and improved its texture profile, decreasing its hardness and increasing its cohesion. The crumb structure was greatly improved by the treatment and better shape was obtained for GFBs based on LRF and MRF. Therefore, LPH could be an adequate physical treatment to improve the breadmaking properties of RF used in GF breadmaking. In the third part of our investigation, the DIC treatment applied to the RFF allowed to obtain an optimum GFB with saturated steam pressure of 0.3 MPa (Temperature of 132.5°C) for short treatment time of 20 s. This optimum GFB was classified at the same level as the control wheat bread, with the highest Vsp (2.7 ± 0.04 cm3/g) with a gain of 10.20% compared to the GFB control (2.45 ± 0 .04 cm3/g). The crumb grain of our GFB optimum showed a larger structure with a greater alveoli number. Therefore, DIC treatment of our RFF was an effective mean to improve the GFB technological quality.