The effect of freeze-thaw cycling on the quality of Sorghum noodles: An analysis based on starch, moisture and structural characteristics

The effects of freeze-thaw cycles (FTC) on the starch gel structure of extrusion-cooked sorghum flour (ECSF) and natural sorghum flour (NSF) were investigated. The analysis elucidated the influence of FTC on moisture migration and structural characteristics in extrusion-cooked sorghum noodles (ECSN) and natural sorghum flour (NSF). Results indicate that ECSF exhibits V-type starch crystallinity, whereas NSF displays A-type crystallinity. After six cycles of FTC, the DOC of ECSF was 37.79 ± 0.11%, with the R₁₁₄₈/₁₀₇₈ and R₉₆₆/₁₀₇₈ being 1.3197 ± 0.0014 and 1.2292 ± 0.0011, respectively. All these values were lower than those of NSF. For ECSN samples, the free water content, hardness, chewiness, cooking loss and color difference were 76.30 ± 0.54%, 13.06 ± 0.34 N, 78.99 ± 1.69 mJ, 14.63 ± 0.11% and 12.75 ± 1.27, respectively. All of which were lower than the corresponding indices of NSN. In contrast, its springiness (0.78 ± 0.04 mm), cohesiveness (0.42 ± 0.02), adhesion (24.50 ± 0.66) and water absorption (10.26 ± 0.11%) were all higher than those of NSN. At the same number of FTC, both the elastic and viscous modulus of ECSN were higher than those of NSN. Microstructural observations showed that ECSN had a continuous protein-gluten network structure without starch granule precipitation. These results indicate that ECSN prepared by adding ECNF can effectively resist the internal structural damage of frozen foods caused by FTCs and maintain good product quality. This research provides theoretical foundations for enhancing the frozen storage and freeze-thaw quality of sorghum-based processed foods.