Effect of drying method and hydrothermal treatment of pregelatinized Hylon VII starch on resistant starch content

The effect of pregelatinization and drying method in resistant starch (RS) content of high amylose starch (Hylon VII, 70% amylose content) was studied. Starch was subjected to autoclaving pre-gelatinization (40% starch suspension w/w, 121 °C) for 30 min. Oven-drying (OD) at 40 °C for 24 h and freezing-drying (FD) methods were used. Subsequently, hydrothermal treatment (HT) with 40% water content at 100 °C for 3, 12 and 24 h was applied to dried samples. Pre-gelatinization decreased the RS content by about 25% with respect to the Hylon VII starch. The drying method affected the RS content, with OD increasing and FD decreasing the RS content. HT time affected positively the RS content for OD starch, whilst the opposite effect was obtained for FD starch. XRD analysis revealed that B-type crystallinity of native starch was modified by drying and HT. Weak linear correlation (R² = 0.69) between RS content and relative crystallinity was found. However, strong exponential correlation (R² = 0.96) between RS content and short-range ordering quantified by FTIR measurements were found. This suggests that RS is close related to formation of double-helix and amylose-lipid complex (evidenced by the XRD peak at 2θ = 20°) during drying and heat treatment of starch.