Rheological properties of gels obtained from gluten-free raw materials during a short term ageing

The high amount of starch contained in gluten-free baked products is largely responsible for their quality decay during storage. Starch retrogradation, in fact, is the major phenomenon involved in bread staling. The aim of this research was to evaluate the rheological properties of gels obtained from corn starch (CS), rice flour (RF) and their mixtures, and the capability of waxy rice flour (WRF) and rice bran (RB) to reduce starch retrogradation when added at different ratios. Gels were prepared by means of the Brabender® Micro-Visco-Amylograph and their rheological properties during a 7 days storage period at 4°C were evaluated both through compression tests (TA-HDplus Texture Analyzer) and frequency sweep tests (Physica MCR 300 Rheometer). During ageing, gels consistency increased at different extents and rates. Samples containing CS showed the highest consistency: both CS and the mixture 50CS-50RF presented a stiffness of 3.34+/-0.11 N/mm after 7 days of storage and the highest storage modulus (G’). On the contrary, WRF originated very weak gels and resulted more effective than RB in delaying gel hardening: WRF, 50RF-50WRF and 50CS-25RF-25WRF remained rather soft at the end of the storage period, in fact stiffness values varied between 0.14+/-0.02 and 1.63+/-0.02 N/mm. The presence of WRF or RB, both at 25% and 50%, strongly reduced G’ values of the mixtures containing CS or RF. For the same gels, G’ curves overlapped up to seven days, indicating a very slow hardening kinetic. The results obtained in this research thus highlight the possibility to enhance the shelf-life of gluten-free baked products including WRF and/or RB among the other ingredients. The task of the future research is to better identify the proper amount of WRF and/or RB in order to allow an appropriate dough handling and to enhance the softness of the final product during storage.