Effect of steam explosion pre-treatment on molecular structure of sweet potato starch

Purpose: To examine the effect of steam-explosion (SE) strength on the molecular structure of sweet potato starch.
Methods: Sweet potato starch was pre-treated using SE method. The effects of SE pressure and pressure-holding time on the molecular structure of the sweet potato starch were investigated by gel chromatography (GPC), infrared spectroscopy, and grading analysis.
Results: The molecular weight (MW) of the starch pre-treated by SE technology decreased with increasing explosion pressure and pressure-holding time; however, the individual MW of amylopectin and amylose declined from 439,834 and 6578 to 238,603 and 4845, respectively. Furthermore, the peak area ratio (obtained by GPC) of amylopectin decreased from 84.39 to 65.16 % while that of amylose increased from 15.61 to 34.84 %. No new absorption peaks were found in the infrared spectra of sweet potato starch following SE pre-treatment. Crystallization index and median diameter of sweet potato starch increased from 1.661 to 1.959 and from 13.73 μm to 76.36 μm, respectively, with rising pressure and pressure-holding time, following SE pre-treatment.
Conclusion: SE pre-treatment effectively degrades the degree of polymerisation of molecular chains in sweet potato starch and enhances the degree of crystallinity thereof. SE method is an approach for the production of sweet potato starch with high-level anti-digestion characteristics.

Keywords
Sweet potato starch; Steam-explosion; Molecular weight; Degree of crystallinity; Particle diameter