To investigate the effects of different screw configurations on the physicochemical properties and reconstitutability of extruded corn flour, this study set up different screw configurations by varying the number of kneading element groups, the distance between the kneading elements and the die head (kneading-die distance), and the kneading element spacing. The specific mechanical energy was taken to reflect the shear strength of the screw. The paste, hydration, textural properties and microstructure of extruded corn flour were measured as well as its reconstitutability. The results showed that different screw configurations caused changes in specific mechanical energy; compared with that of non-extruded corn flour (NCF), the specific mechanical energy of extruded corn flour was elevated with increasing number of kneading elements and with decreasing kneading-die distance or kneading element spacing, and the starch and water molecules in extruded corn flour formed a highly porous gel structure. When two sets of kneading elements were used and the kneading element spacing was 5 L/D (G6), the peak pasting viscosity and gel hardness of corn flour decreased by 57% and 64.94%, respectively. The relative crystallinity of starch decreased by 62.76%, the water absorption index and water solubility index increased by 1.83 and 2.10 folds, respectively and the agglomeration rate of extruded corn flour decreased by 77.91%, indicating significantly improved reconstitution stability. Correlation analysis showed that the specific mechanical energy of extruded corn flour was significantly and positively correlated with the content of amylose, stability coefficient, water absorption index and water solubility index, but significantly and negatively correlated with the relative crystallinity, agglomeration rate and centrifugal sedimentation rate. The relative crystallinity was significantly and negatively correlated with the water absorption index, water solubility index and stability coefficient, but significantly and positively correlated with the agglomeration rate and centrifugal sedimentation rate. In conclusion, increasing the number of kneading elements and decreasing the element spacing can effectively enhance the physicochemical properties and reconstitutability of extruded corn flour, providing a theoretical basis for the selection of screw configuration for improved reconstitutability of extruded corn flour.

We investigated the changes of gel characteristics and structure of ultrasonically treated corn starch during freeze-thaw cycles, with a view to providing theoretical guidance for improving the quality of quick-frozen starch-based foods. The effects of the number of freeze-thaw cycles on the dynamic rheological and textural properties of ultrasonically modified corn starch gels were analyzed and their structures were characterized by using a rheometer, a texture analyzer, a low-field nuclear magnetic resonance (NMR) spectrometer, a Fourier transform infrared (FTIR) spectrometer and an X-ray diffractometer (XRD). The results showed that compared with native corn starch, the water separation rate of ultrasonically modified corn starch gels significantly decreased by 5.19% (P < 0.05) at the 4th freeze-thaw cycle, indicating improved freeze-thaw stability; the storage modulus and loss modulus of ultrasonically modified corn starch gels decreased, and the gel strength was weaker; the hardness significantly decreased by 10.83% (P < 0.05), and the amylose content decreased 0.15%. Moreover, the iodine binding force was weakened, the transverse relaxation time distribution curve was shifted to the left, the short-range ordered structure was weakened, and the relative crystallinity was reduced. The gel properties and the structural characterization results indicate that ultrasonic treatment can inhibit water migration and double helix structure formation in the corn starch gel system during freeze-thaw cycles and consequently improve its freeze-thaw stability.

In this study, we investigated the effect of high hydrostatic pressure (HHP) treatment on the physicochemical and structural properties of corn starch/ferulic acid (CS/FA) composite system by differential scanning calorimetry (DSC), rheometer, Fourier transform infrared (FTIR) spectroscopy, X-ray diffractometry (XRD). The results showed that HHP treatment enhanced the peak viscosity, elastic modulus G’ and viscous modulus G”, and reduced the solubility and degree of expansion (75–95 ℃), enthalpy of gelatinization, and retrogradation value of the composite system. In addition, HHP treatment increased the particle size of the composite system, and FTIR and XRD spectra showed that the short-range ordered and double helix structure of the composite system decreased after HHP treatment; the starch particles were still A-type, but the relative crystallinity decreased. In summary, HHP treatment promoted the interaction between corn starch and ferulic acid in the composite system, improved the physicochemical properties of corn starch, and reduced its ordered structure.

The effect of co-fermentation with yeast and lactic acid bacteria on the physicochemical properties of cornmeal batter and the quality of steamed sponge cake was investigated using a rapid viscosity analyzer, a rheometer, a differential scanning calorimeter (DSC), low-field nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FTIR) spectroscopy and a texture analyzer in this study. The results showed that as fermentation proceeded, the co-fermented batter had higher gas-producing and gas-holding capacity than the single-culture fermentations. The peak viscosity of the co-fermented batter showed a decreasing trend, decreasing by 11.66% after 90 min of fermentation, the gelatinization enthalpy and the degree of short-range ordering of starch molecules tended to increase, and the viscoelasticity and the content of strongly bound water showed a tendency to first increase and then decrease. The greatest viscoelasticity, the smallest tan δ, and the most stable structure were observed after 50 min of co-fermentation, and steamed sponge cake made from the fermented corn batter had the largest specific volume, the lowest hardness and gumminess, and the highest cohesiveness and resilience. The results of this study provide a reliable technical basis for the corn-based staple food industry.

In order to improve the processing characteristics of corn flour, the effect of twin-screw extrusion on the microstructure and physicochemical properties of corn flour was evaluated under different conditions of moisture content (15%, 18%, 21%, and 24%) and extrusion temperature (100, 120, 140, and 160 ℃). The results showed that after extrusion, the morphology of starch granules was destroyed, resulting in water absorption and swelling of the starch and gel network formation, significantly improving the hydration characteristics, cold paste viscosity and pseudoplasticity of corn flour (P < 0.05). With increasing extrusion temperature or moisture content, the damage degree of starch crystalline zone and double helix structure became more and more serious. At a moisture content of 18% and an extrusion temperature of 120 ℃, the maximum tensile distance of (28.95 ± 0.66) mm was recorded, indicating the strongest pseudoplasticity. Taken collectively, extrusion modification could effectively improve the problem of the difficulty in molding corn flour due to the lack of gluten protein, which will provide a technical basis for the processing of whole corn staple foods.