Whole white corn was ground, and lime, water and xanthan gum (XG, 0.5% w/w), carboxymethylcellulose (CMC, 0.5% w/w), guar gum (GG, 0.5% w/w) or a gums mix (XG, 0.25% w/w; CMC, 0.15% w/w; GG, 0.10% w/w) were added. Blends were extruded, dried and ground to obtain nixtamalized corn flour (ENCF), and they were used to make tortillas. The particle size distribution, particle size index, water absorption capacity (WAC) and water absorption index (WAI) were determined in flour; moisture content and viscoelastic characteristics (G′, G′′, tan δ) were determined in corn masa; tortillas were made, and texture (cutting force and rollability) and sensory evaluation were carried out. ENCF with XG and gums mix had the highest WAC, and tortillas were softer (33%) than tortillas from ENCF without gums. Corn masa viscoelasticity (tan δ) correlated negatively with tortilla firmness (r = −0.84). Corn tortillas made with XG and gums mix had acceptable organoleptic characteristics. PRACTICAL APPLICATION The extrusion process allows the using of the whole corn to make tortillas and reduce processing costs and the contaminant effluents (cooking liquor). The addition of a mix of gums during extrusion makes the corn masa retain more water and modify its rheological properties, improving masa handling characteristics and tortilla textural quality. The evaluation of masa viscoelasticity with the dynamic method makes it possible to differentiate corn masas and to select the best treatments.

This research aimed to prepare instant flour from malted and raw (un-malted) corn flours nixtamalized by the extrusion process and evaluate the effect on the physicochemical properties of tortillas prepared using these flours. White maize was malted for 24 h, dried at 50 ± 1 °C, and ground. Subsequently, 0.3 % lime and 25 or 30 % water were added to ground malted or un-malted corn, and the mixture was refrigerated (4 °C) for 12 h. These samples were nixtamalized by an extrusion process in a single screw extruder at two temperature profiles within four heating zones, TP1 (60, 60, 70, and 80 °C) and TP2 (60, 70, 80, and 90 °C), to obtain corn flour. Water was added to the extruded corn flours to make a dough, or masa, and the masa was then molded and baked to obtain tortillas. The corn flours were characterized according to their ability to absorb water and viscosity profile (RVA). The firmness and rollability after 2 and 24 h of storage were determined, and a sensory evaluation was conducted. The malted corn flour extruded with a 25 % moisture content and TP2 temperature profile yielded tortillas with the best firmness and rollability. In conclusion, the changes during the malting of corn grain and the nixtamalization by the extrusion process improved the water absorption capacity of flours and textural properties of the tortilla and produced a product with acceptable sensory properties.

Physically modified extruded flours are suitable ingredients for cold preparation of products such as creams and sauces. The rheological and textural properties and stability of model sauces prepared with wheat and rice extruded flours with three different particle size fractions were assessed. All tested sauces showed non-Newtonian, shear-thinning and thixotropic fluid characteristics. Sauces made with rice extruded flours, with lower protein and amylose contents, presented lower shear-thinning behaviour, consistency index and yield stress than wheat based sauces. Rice sauces also displayed a less compact microstructure and lower viscoelastic character but a higher resistance to freeze-thaw process. Regarding particle size, the finest flours showed lower values of consistency index, yield stress, and G' and G'' moduli but led to higher syneresis. Overall, results proved that pregelatinised extruded flours can be used in sauces applications without heating, but their properties greatly depend on the cereal type and its particle size.