Abstract
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
Highlights
Steam-explosion (SE) treatment, developed by WH Mason in 1928, is a method used for pretreating biomasses by heating raw materials to between 0.69 and 4.83 MPa for several seconds using saturated steam at 160 to 260 °C and reducing the pressure suddenly to atmospheric pressure [1]
The primary working principle of SE is to expose raw materials to steam under high temperature and pressure for a specific period of time where the materials swell owing to the presence of the overheated liquid and their pores are filled with steam
The sweet potato starch were pre-treated by use of the proposed SE technology to study the effects of explosion pressure and pressureholding time on the molecular weight (MW) distribution of the sweet potato starch, the gel chromatograms are shown in Figure 2 and Figure 3
Summary
Steam-explosion (SE) treatment, developed by WH Mason in 1928, is a method used for pretreating biomasses by heating raw materials to between 0.69 and 4.83 MPa for several seconds (or even minutes) using saturated steam at 160 to 260 °C and reducing the pressure suddenly to atmospheric pressure [1]. When the high pressure is rapidly released to the surrounding environment (within 0.00875 s), the water vapour inside the materials expands and exerts pressure on the cell walls, which causes the materials to undergo explosive decompression [2,3,4]. It has been 80 years since the technology was first proposed, SE treatment is used for treating wood fibres to separate components and change the structure of fibrous materials, so as to improve the accessibility of celluloses to enzymes and chemical reagents [57]. SE has been increasingly considered as one of the most efficient, environmentally friendly, and costeffective pre-treatment methods for transforming biomass resources and can be carried out on a large scale [8]
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