Rheological behaviour of rice flour gels during formation : influence of the amylose content and of the hydrothermal and mechanical history

Rice starches and flours have unique attributes that make them interesting ingredients in the food industry (e.g. hypo-allergenic, gluten-free, bland in flavour, capable of giving consistency). In particular, the rheological properties of the starchy matrix during food processing and storage strongly influence the quality and shelf-life of the final products. Even though several works in literature concern rice gels rheology, none of them deeply investigated the steps associated with the conversion of rice slurries into gels, and the influence of the thermal and mechanical history, in addition to flour composition, on the rheological properties of the resulting gels. This study explores the variations in the rheological properties of the slurries obtained from two rice flours having a different amylose content and subjected to specific hydrothermal and mechanical profiles while developing into gels. First, rice flours were characterized for their proximate composition and pasting properties. Then, the slurries collected after different processing times were submitted to fundamental rheological measurements. Additional evaluations were performed on the gels during 4 days ageing at 4 °C. The amylose content strongly influenced the pasting profiles and the viscoelastic properties of the developing gels to different extents in relation to their hydrothermal history. Results evidenced that the thickening and networking action are determined mainly by the starch amount during the first stages of gel development, and by the amylose content later on. The obtained results can be useful in fully understanding the rice gel behaviour and in addressing the processability of rice flour for food applications.