Determining the effects of annealing time on the glass transition temperature of Pueraria lobata (Willd.) Ohwi starch

To probe the effects of annealing time on the glass transition temperature (T_g) and digestibility of Pueraria lobata (Willd.) Ohwi starch, the starch crystal structure and moisture distribution through the components of P. lobata (Willd.) Ohwi starch were investigated. Annealing times of 0, 1, 3, 6, 12 and 24 h were employed to determine the effect of starch T_g using differential scanning calorimetry (DSC) with the support of ¹H low‐field NMR, polarised light microscopy and ¹³C CP/MAS NMR. The T_g values of the starch increased with longer annealing times. The ¹H low‐field NMR results showed that the T₂ relaxation time decreased and starch–water interactions increased as the annealing time increased. Compared with native starch, annealed starch had higher contents of slowly digested starch (SDS) and resistant starch (RS). The starch crystal structure was not destroyed after annealing, but the relative crystallinity percentage increased slightly.