Native starches were isolated from mature grains of high-amylose transgenic rice TRS and its wild-type rice TQ and treated with 0.1% and 0.4% NaOH for 7 and 14 days at 35 °C. Alkali-treated starches were characterised for structural and functional properties using various physical methods. The 0.1% NaOH treatment had no significant effect on structural and functional properties of starches except that it markedly increased the hydrolysis of starch by amylolytic enzymes. The 0.4% NaOH treatment resulted in some changes in structural and functional properties of starches. The alkali treatment affected granule morphology and decreased the electron density between crystalline and amorphous lamellae of starch. The effect of alkali on the crystalline structure including long- and short-range ordered structure was not pronounced. Compared with control starch, alkali-treated TRS starches had lower amylose content, higher onset and peak gelatinisation temperatures, and faster hydrolysis of starch by HCl and amylolytic enzymes.
Keywords: (13)C CP/MAS NMR; (13)C cross-polarisation magic-angle spinning nuclear magnetic resonance; AAG; ATR-FTIR; Alkali treatment; Aspergillus niger amyloglucosidase; DSC; Functional property; High-amylose starch; PPA; RS; Rice; SAXS; SBE; SEM; Structural property; TQ; TRS; Te-qing (wild type rice cultivar); X-ray powder diffraction; XRD; attenuated total reflectance–Fourier transform infrared; differential scanning calorimetry; porcine pancreatic α-amylase; resistant starch; scanning electron microscope; small-angle X-ray scattering; starch branching enzyme; transgenic rice line.
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