Effects of extrusion cooking and low-temperature storage on the physicochemical changes and resistant starch (RS) content in cornstarch were evaluated. The cornstarch was conditioned at 20%-40% moisture contents and extruded in the range 90-130 • C and at screw speeds in the range 200-360 rpm. The extrudates were stored at 4 • C for 120 h and then at room temperature. The water absorption, solubility index, RS content, viscoelastic, thermal, and microstructural properties of the extrudates were evaluated before and after storage. The extrusion temperature and moisture content significantly affected the physicochemical properties of the extrudates before and after storage. The RS content increased with increasing moisture content and extrusion temperature, and the viscoelastic and thermal properties showed related behaviors. Microscopic analysis showed that extrusion cooking damaged the native starch structure, producing gelatinization and retrogradation and forming RS. The starch containing 35% moisture and extruded at 120 • C and 320 rpm produced the most RS (1.13 g/100 g) after to storage at low temperature. Although the RS formation was low, the results suggest that extrusion cooking could be advantageous for RS production and application in the food industry since it is a pollution less, continuous process requiring only a short residence time.

Effects of extrusion cooking process (ECP) with citric acid (CA) addition on the physicochemical changes and resistant starch (RS) formation in native corn starch (NCS) are evaluated. NCS at different feed moisture levels (18–32%) and CA concentrations (0–10.3%), are subject ECP under constant conditions of screw speed (233 rpm) and die temperature (127 °C). The obtained extrudates are stored at 4 °C for 120 h and then at room temperature. The water absorption index (WAI), water solubility index (WSI), RS content, peak temperature (Tp), ∆H, peak viscosity (PV), setback viscosity (SV), FT‐IR, X‐ray analysis and microstructural (SEM) properties are evaluated. RS content and WSI increased with decreasing moisture content (MC), WAI, PV and SV shows that increases in MC caused an increase, while ∆H and Tp decreases with decreasing MC. SEM shows that ECP with CA destroys the granular structure of NCS generated amorphous structures owing to gelatinization and dextrinization. FT‐IR analysis shows that extruded samples with CA cause starch hydrolysis, increasing the intensity of bands 994 and 1016 cm−1 in comparison to NCS. The highest RS yield (1.15 g/100 g) is obtained at 18% moisture content and 5.2% of CA: an increase of 71% with respect to NCS.

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Acid hydrolysis process (AHPS) combined with hydrothermal storage process (HSPS) and extrusion cooking process (ECPS) are performed to obtain resistant starch (RS) from corn starch (CS). CS is subjected to AHPS citric, phosphoric acids, and HCl and thermal processes: 1) ECPS at 100 °C, 18% moisture content, and 220 rpm; 2) HSPS at 120 °C for 1 h, then storing at low temperature (4 °C) for 24 h. Evaluations in the different treatments are: RS, water absorption index (WAI) and solubility index (WSI); rheological, thermal, and microstructural properties. Treatment HAL results in the highest yield of RS (13.19 g/100 g), which increases WAI and WSI, low viscosity, gel hardness, ΔH and microstructural analysis showing agglomerated structures (30 µm) of diameter. On the other hand, HAC and HAP generated values of RS (8.47–9.19 g/100 g), respectively. Results show that pre‐treatment by AHPS combined with HSPS is an alternative for obtaining RS, which exhibits suitable physical properties and is applicable to different dietary matrixes, at a 20‐fold increased yield.

Effects of different β-glucan concentrations in maize flour on the properties of frozen maize tortillas were evaluated. Masa (dough), pre-cooked (PTs), frozen (FTs), thawed (TTs), and cooked tortillas (CTs) were made and analyzed. Moisture content of masa and tortillas significantly decreased as β-glucan concentration increased; however, the water absorption capacity (WAC), ice melting enthalpy, and frozen water in FTs increased. Texture and color of the masa, PTs, and CTs as well as sensory analysis showed differences only between tortillas with 0% and 4% β-glucans. β-glucans did not affect the texture of CTs. Soluble fiber increased by over threefold and fivefold in tortillas with 2% and 4% β-glucans, respectively, than in those without β-glucans. This result was consistent with the observed structural changes in tortillas, showing an increase in high-fiber aggregates with increasing β-glucan concentration. Tortillas with 2% β-glucans showed acceptable physicochemical, functional, and sensory properties, but over three times the soluble fiber. Therefore, it is possible to obtain frozen tortillas with high fiber content and increase their shelf life for subsequent cooking while maintaining good properties.Keywords: maize flours; frozen tortillas, β-glucans; dietary fiber; soluble fiber.Practical Application: Nixtamalization is a process through which maize is cooked to obtain mainly instant flours for making tortillas. However, the pericarp removed during this process result in flours with low fiber content. This research presents an alternative to enrich maize flours with β-glucans to produce high fiber tortillas and frozen to extend their short shelf life as alternative for storage and increase their availability of fresh tortillas. Frozen tortillas with fiber added showed acceptable properties compared to commercial tortillas, but with over triple of soluble fiber.