Quinoa is one of the most popular ingredients in the creation of healthy and environmentally friendly foods, due to its rich nutrient composition, balanced amino acids, and various bioactive substances. Quinoa noodles can be prepared for green and healthy food, particularly for better taste and market prospects. However, the traditional processing of wheat noodles cannot fully meet the high quality of quinoa noodles at present, due to the lack of gluten. Among them, extrusion has been applied to prepare the whole quinoa noodles. The natural color of food can also be closely related to its nutritional value. Quinoa grains with different colors often vary in the content of starch, protein, fat, fiber, and active substances. This study aims to clarify the great influence on the cooking and nutritional quality of extruded noodles made with quinoa as raw materials. The mechanism of quality of extruded quinoa noodles with different colors was explored to compare the basic components, gelatinization of quinoa flours, the microstructure, cooking quality, active components, and starch digestion. Results showed that the white quinoa achieved the highest content of total starch and crude fiber, compared with the red and black quinoa powder. The content of crude fiber increased significantly with the deepening of the color of quinoa powder. Among the three types of quinoa powder, the red quinoa exhibited the highest levels of fat and protein content. In terms of gelatinization properties, the peak viscosity, final viscosity, and setback value of white quinoa powder were superior to those of red and black quinoa powder. The pasting temperature of white quinoa powder was lower than that of red and black quinoa powder. Furthermore, L* values significantly decreased after extrusion, whereas, a* value and b* values significantly increased (P < 0.05). Additionally, the red and black quinoa powder, along with their extruded noodles, exhibited higher levels of polyphenols, flavonoids, and antioxidant activities, compared with the white quinoa. X-ray diffraction revealed that the extrusion process caused the changes of starch crystal type from type A to V. There was a decrease of starch crystallinity in the white, red, and black quinoa noodles from 17.12%, 25.55%, and 21.41% to 10.53%, 8.06% and 7.71%, respectively. White quinoa noodles shared the highest crystallinity, due to the high starch content and high setback value of powder. The recrystallization of starch formed a relatively stable and orderly molecular structure, thus enhancing the crystallinity of starch in the extruded quinoa noodles. Although the cooking time of red and black quinoa extruded noodles was shorter than that of white ones, their overall cooking quality was notably inferior. The cooking loss of white quinoa noodles was 7.46%, which was significantly lower than that of red (10.12%) and black (9.16%). At the same time, the extruded white quinoa noodles also exhibited the highest hardness (30.71 N) and springiness (0.97). The extruded noodles relied primarily on the gelatinization and retrogradation of starch. The rearrangement of starch was dominated to form a stable gel structure after extrusion for the cooking quality of extruded quinoa noodles. Scanning electron microscope images confirmed that the gel network structure of white quinoa extruded noodles was denser and more complete, thereby leading to the lower cooking loss and superior texture, compared with the red and black quinoa extruded noodles. The in vitro starch digestibility showed that the white quinoa noodles contained the highest resistant starch content and the lowest predicted glycemic index of 68.56. In summary, the red and black quinoa presented a relatively higher content of active substances, but white quinoa was more suitable for the production of high-quality and low-GI extruded noodles. This finding can provide the theoretical and technical reference for the production and processing of high-quality quinoa noodles.
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Based on the freeze-thaw stability of quinoa stabilized Pickering emulsion, it was incorporated evenly into surimi to generate surimi gels in this study, and its feasibility to improve the freeze-thaw stability of fish protein gel was evaluated. This research aimed to prevent the deterioration of fish protein gel, caused by the temperature fluctuation during storage and transportation.
Quinoa protein Pickering emulsion was prepared and distributed in surimi, followed by heating process to generate surimi gels. The surimi gels with different contents of Pickering emulsion and without emulsion were subjected to three freeze-thaw cycles, and then, the texture, color, water and ice crystal distribution and drip loss of surimi gels were measured.
The quinoa protein Pickering emulsion improved the lightness and whiteness of fish surimi gel, and inhibited the changes of color after freeze-thaw cycles. Meanwhile, the Pickering emulsion addition delayed the changes of hardness and chewiness of surimi gels during freeze-thaw cycles. It was found that quinoa protein Pickering emulsion had no effect on the moisture distribution of surimi gels before freeze-thaw cycles, but significantly increased the proportion of immobile water and decreased free water content in surimi gels after freeze-thaw cycles. Therefore, the drip loss of surimi gel was decreased by emulsion addition. Furthermore, the emulsion addition decreased the diameter of ice crystals formed in surimi gel, reduced the damage to muscle tissues, and decreased the free water content.
The Quinoa protein Pickering emulsion weakened the adverse impact of freeze-thaw cycles on the color and textural properties, maintained the gel structure, and improved the freeze-thaw stability of fish surimi gel, which maintained its quality and nutritional value. Quinoa protein Pickering emulsion was promising to become an innovative antifreeze to be applied in frozen food.
This research studied the effects of different salt ions on the gel properties of quinoa protein, and explored its molecular mechanisms, so as to provide a theoretical basis for the processing of quinoa protein gels.
Quinoa protein was extracted by alkali extraction and acid precipitation. Quinoa protein solution (20%, w/v) was prepared at pH 7.0. NaCl, CaCl2, CaSO4 and MgCl2 was added in quinoa protein solution till the concentration was 50 mmol∙L-1, and then the solution was heated in a water bath to prepare quinoa protein gels. The effects of salt ions on the texture, water retention, color properties and water distribution of quinoa protein gels were analyzed. Meanwhile, the effects of salt ions on the microstructure and rheological properties of quinoa protein gels were studied by scanning electron microscopy and rheometer. The effects of salt ions on the molecular interactions and secondary structure of protein gels were also analyzed.
The addition of salt ions significantly decreased the hardness and water holding capacity, while increased the springiness of quinoa protein gels under pH 7.0. Quinoa protein gels with MgCl2 showed the lowest hardness and water holding capacity. NaCl addition had no significant influence on the color properties of protein gels. However, the addition of bivalent salt ions significantly improved the lightness and whiteness of quinoa protein gels, and their whiteness increased from 59.62 to 67.80 with the addition of CaCl2. Furthermore, the addition of salt ions promoted granular aggregation of quinoa protein, which made the gel network structure become coarse. Coarse and larger gaps were observed in the microstructure of quinoa protein gels when divalent salt ions were added. Meanwhile, compared with blank gels and gels added with NaCl, the addition of divalent salt ions significantly decreased the content of disulfide bond, and weakened the electrostatic interactions within quinoa protein gels. Furthermore, the addition of salt ions decreased the contents of β-sheets and β-turns, increased the contents of α-helix and random coil, which affected the orderliness of protein secondary structure.
Under neutral conditions, the gel properties of quinoa protein and microstructure of gels were affected by the presence of different salt ions to various degrees. Compared with the gel prepared with NaCl, quinoa protein gels with the same concentration of CaCl2, CaSO4, and MgCl2 showed rougher microstructure, lower gel hardness and water holding capacity, as divalent salt ions significantly decreased the disulfide bond content and weakened the electrostatic interactions within quinoa protein gels.
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