High amycea starch recombinant rice (HMER) and extruded blank rice (ER) are close to raw rice (NR) in transparency and color, while oat dietary fiber recombinant rice (DFER) and rice protein recombinant rice (RPER) are yellow-brown and rough in appearance. The addition of oat dietary fiber, rice protein and high amycea starch will have a certain effect on the gelatinization degree of recombinant rice, among which HMER has the lowest gelatinization degree. Oat dietary fiber and high acrylate corn starch promote starch aging of extruded recombinant rice, while rice protein inhibits starch aging of extruded recombinant rice. Oat dietary fiber, rice protein and high amycorn starch can all improve the stability of recombinant rice starch paste, among which high-acrylate cornstarch is the most significant. The addition of rice protein and oat dietary fiber makes recombinant rice easier to regenerate, while the addition of high-acrylic corn starch can reduce the degree of regeneration of extruded recombinant rice, which may better maintain the texture of cold rice.
Due to the high temperature and high pressure effect of extrusion, the RDS (fast digesting starch) content of extruded rice increases compared to the original rice, and the content of SDS (slow digesting starch) decreases. Due to the high amylose content of HMER, more resistant starch (RS3 type) is formed during aging and maintains a high retention rate after cooking. After cooking, the starch hydrolysis rate and GI value of HMER were significantly lower than ER and NR, and the starch hydrolysis rate and GI value of DFER and RPER were not significantly different from ER, and significantly higher than NR, because HMER had high amylose content and was more difficult to digest enzymatically. Combining GI and GL, high amycea starch has the best effect on reducing blood sugar in recombinant rice.
The ripening time, water absorption, volume expansion rate and solid loss of the four groups of extruded recombinant rice were lower than NR. The three additives had no significant effect on the water uptake, volume expansion rate and ripening time of extruded recombinant rice. The addition of rice protein increased the loss of solids in recombinant rice, while the addition of oat dietary fiber and high amycea starch had no effect. Recombinant rice is superior to virgin rice in terms of solids loss and ripening time. Compared with extruded blank rice, the addition of rice protein reduced the hardness and elasticity of recombinant rice, and the viscosity had no significant effect, while the addition of oat dietary fiber and high amycea starch had no significant effect on hardness, viscosity and elasticity. Compared with the original rice, the hardness of recombinant rice was significantly reduced, and the other recombinant rice was significantly increased except for the decrease in RPER viscosity. The comprehensive sensory scores of each extruded recombinant rice under the best cooking conditions were lower than those of the original rice, and the HMER sensory score was the closest to the original rice, followed by DFER and the worst RPER.