Effect of freeze-thawing treatment on the structural and physicochemical characteristics of starch isolated from Chinese yam

Abstract

Freeze-thaw (F/T) is an effective physical method for modifying starch, improving its structures and physicochemical properties. This study investigated the effects of varying F/T cycles on the fine structure (molecular chain, short-range order, crystal, and particle structures) and physicochemical properties (solubility, swelling power, pasting and thermal properties, and digestibility) of Chinese yam starch (NCYS). The modified starches showed reduced amylose (19.11 %–20.08 %) and A chain content (9.71 %–10.69 %), while B3 chain content increased (49.07 %–54.90 %). Compared to NCYS, the modified starches exhibited a weaker short-range ordered structure, higher double helix content (58.76 %–59.83 %), and increased crystallinity (43.52 %–46.98 %). The modified starches showed higher pasting temperature (86.9–87.2 °C), lower breakdown viscosity (1432–1564 cP), and higher setback viscosity (1840–2033.5 cP) compared to NCYS. Additionally, the modified starches had higher T_o (76.45–76.64 °C) and △H (9.93–10.92 J/g) than the native starch. Morphological analysis revealed surface roughening and loss of granule integrity. Enhanced anti-digestion properties were observed, with a reduction in rapidly digestible starch (1.49 %–3.00 %) and an increase in resistant starch (94.41 %–96.76 %). This study provides insights into the modifications of Chinese yam starch through F/T treatment, highlighting its promising applications in functional food development.