Corn starch was subjected to enzymatic biotechnology with thermostableα-amylase and pullulanase and followed by retrogradation, to prepare resistant starch. The properties of selected resistant starch (RS) samples were also investigated. The result showed that, appropriate amount (0.5 U/g) of thermostable α-amylase was good for resistant starch formation. The optimal condition for pullulanase hydrolysis was carried out with 0.8 PUN/g (dry starch) pullulanase in pH 5.5 starch gel at 60°C for 12 h. The highest yield of resistant starch could be obtained (19.02%) under optimal condition. The effect of pullulanase on resistant starch formation was the most significant. Compared with native starch, amylose content was increased by 17.0 to 28.1% and it did not increased with enhancement of resistant starch content. The native starch showed A-type X-ray diffraction pattern, whereas RS products exhibited B-type pattern with strong intensity at the peak of 17.2°C 2θ and two board peak at 20.1 and 23.9°C 2θ. The transformation enthalpy of the second peak increased gradually with increasing RS content and the transformation peak temperature and Tc-T0 was also similar to this trend.
Key words: Resistant starch, thermostable α-amylase, pullulanase, properties.
RS, Resistant starch; RS1, physically inaccessible starch; RS2,resistant starch granules; RS3, retrograded starch; RS4, chemically modified fragments; DMSO, dimethyl-sulphoxide; DSC, differential scanning calorimetry.
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