Thermal and enzymatic degradation induced ultrastructure changes in canna starch: Further insights into short-range and long-range structural orders

• Crystal stabilization was observed in TDCS and EDCS.
• The short-range order of starch correlated well with long-range order.
• The degradation procedure helped compact the starch granules.
• The crystalline volume fraction did not align with crystalline weight fraction.

Slurries of canna starch treated with or without α-amylase were heated at 60 °C to investigate the mechanism of thermal and enzymatic degradation and the effects of these processes on the ultrastructure of starch residues. For this purpose, solid-state 13C CP/MAS NMR, X-ray diffraction (XRD), and small angle X-ray scattering (SAXS) were used to estimate the short- and long-range orders within the structure. Crystal stabilization was observed in both samples of thermally degraded canna starch (TDCS) and enzymatically degraded canna starch (EDCS), and the critical time for the formation of double helical crystals was 3 h for thermal degradation and 5 h for enzymatic degradation. With longer times, imperfect sub-crystal started prevailed. The results showed that when degradation occurs, the crystal lamellae compact, as indicated by a higher crystal density in the structure of EDCS. Moreover, the relationship between crystalline weight and volume fraction as well as short-range and long-range orders were also investigated and found correlate well with each other.

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