Effects of moisture content on digestible fragments and molecular structures of high amylose jackfruit starch prepared by improved extrusion cooking technology

The effects of different moisture contents on the digestible fragments and molecular structures of high amylose jackfruit starch were investigated. The digestible fragments and molecular structures of rapidly digestible starch, slowly digestible starch and resistant starch of high amylose jackfruit starch with different moisture contents prepared by improved extrusion cooking technology were analyzed. Decreasing the moisture content resulted in significant decrease in slowly digestible starch and resistant starch content (24.08% and 25.99%–17.59% and 16.60%), indicating that high amylose jackfruit starch with low moisture content was easier to digest. Compared to extruded control starches, the slowly digestible starch + resistant starch fraction and resistant starch samples exhibited higher gelatinization enthalpy, relative crystallinity, and short - range molecular order, but no significant difference was showed in gelatinization temperature. It was also found that the double helix degree, crystallinity and order degree of the extruded controls, slowly digestible starch + resistant starch fractions and resistant starch samples were increased with increasing moisture content, from 1.74 J/g, 1.52% and 0.207–9.52 J/g, 32.54% and 0.779, respectively. The above results were further supported by the microstructural and porosity analysis that the extruded samples were changed from coarser surface structure to more compact structure with increasing moisture content. All these results indicate that moisture content affects the digestible fragments and molecular structures of starch. Therefore, it can provide a theoretical basis for the modification of high amylose starch, especially for the modification of resistant starch.