Physicochemical properties and conformational structures of pre-cooked wheat gluten during freeze-thaw cycles affected by curdlan

To comprehend the decline in post-production of pre-cooked flour products, this study examined the impact of curdlan on structural properties and aggregation behavior of pre-cooked wheat gluten (PCWG) during freeze-thaw (FT) cycling. The results revealed that as the number of FT cycles increased, the gel fracture strength and distance of PCWG decreased, while the extractable protein increased. The extent of PCWG deterioration increased with more FT cycles. However, the addition of curdlan mitigated these changes, with a notable effect seen at 0.5% (w/w) addition. Microstructural analysis indicated curdlan's role in enhancing PCWG homogeneity. Secondary structure analysis demonstrated a transition in PCWG's secondary structure from β-sheets to random coils and β-turns as the FT cycle increased. Notably, 0.5% curdlan significantly inhibited this transition. The chemical interaction results suggested that curdlan's impact on changing PCWG's structure was linked to shifts in free sulfhydryl groups, disulfide bonds, and hydrophobic interactions. As the FT cycle increased, the free sulfhydryl content in PCWG rose, while the disulfide bond content decreased. Hydrogen bonding decreased, and hydrophobic interactions increased. These trends were effectively countered by low doses of curdlan (especially 0.5%). However, excess curdlan (0.9%) exacerbated the disruption of PCWG's protein network structure during FT cycling, potentially through steric hindrance effects or hydrogen bonding. In conclusion, this study provides theoretical support for enhancing the quality of PCWG and employing curdlan in frozen flour products.