Effect of thermal treatments on rice flour and cooking behavior of rice pasta

Starch is the key component in gluten-free pasta (GFP). Despite that, few studies have dealt with starch properties in GFP. In this work, two experimental rice pasta samples were prepared according to two technologies - conventional and extrusion-cooking - avoiding the use of additives. Pasta R was prepared from rice flour (RF) that was heated by steam (2.5atm, 10 min) in a gelatinization tank. The pre-treated dough was subjected to a first extrusion at 120°C (cooking-extrusion) and formed into pellets which were transferred into a continuous extruder for semolina pasta for the second extrusion step at 50°C and 10 MPa. Pasta P was prepared from a pregelatinized rice flour (PRF) that was directly extruded in the continuous extrusion press at 50°C. Several physical indices were used to compare the properties of the two rice flours, and the relationship between starch properties in dried pasta and its cooking behavior was investigated. After pregelatinization, PRF exhibited a higher viscosity at 30°C, a lower pasting temperature, and a higher susceptibility to alpha-amylase hydrolysis compared to NF. As for pasta, both extrusion conditions promoted further changes in starch properties. When compared to Pasta R, Pasta P was characterized by a lower pasting temperature, by a greater swelling capacity, and by a higher viscosity during heating, resulting in a cooked product with higher firmness. However, both samples of rice pasta exhibited higher cooking loss and lower firmness than semolina pasta. Further studies will focus on the improvement of GFP quality by optimizing the cooking-extrusion conditions and/or by investigating the role of additional texturing proteins.