Diabetes is a chronic disease that jeopardises human health. In China, the prevalence of diabetes in adults is as high as 12.8% (Tang, Luo, Li, Wang, & Li, 2023). Resistant starch (RS) refers to starch that cannot be broken down and absorbed within 120 min in the human small intestine and is important for the control of diabetes (Amonsou, 2023).

RS is closely related to the multiscale structure of starch (granular size, morphology, specific surface area, molecular weight, chain length distribution, amylose/amylopectin content, and crystallinity) (Hu et al., 2023). For example, the greater the specific surface area of a granule, the greater the rate of starch hydrolysis; the higher the amylopectin content, the higher the hydrolysis rate; and the higher the average molecular weight, the higher the amylopectin content of resistant starch.

Table 1 indicates that the relationship between the RS content and relative crystallinity of starch is inconsistent between different studies. For example, Hu et al. found that the relative crystallinity and RS content of wheat starch were significantly decreased after high-pressure treatment. However, Bajaj et al. found that, after high-pressure treatment, the relative crystallinity of wheat starch decreased, but the RS content increased significantly (Bajaj, Singh, Ghumman, Kaur, & Mishra, 2021). Xu et al. found that the relative crystallinity of raw potato starch was only 19.6%, but its RS content was as high as 58.1% (Xu et al., 2018). Chi et al. found that raw potato starch had a relative crystallinity of 25.5% but contained only 5.5% RS (Chi et al., 2019). Therefore, the relationship between the RS content and starch crystalline structure needs to be further studied.

Studies have shown that the relative crystallinity of natural starch granules ranges from 15% to 45% (Chen, Zhong, Yao, Pu, & Huang, 2023). Current research largely agrees that the crystalline structure of starch results from the regular arrangement of double-helical structures. This double-helix structure is formed by the side chains of amylopectin and is the smallest unit of starch crystallisation. In a previous study, the double helix of a starch molecule was modelled. Many intramolecular hydrogen bonds exist in the double-helix structure (Chen, Huang, Pu, Yang, & Fang, 2020). In addition, a previous study found that this double-helix structure is highly stable under high pressure, heat, and salt treatments (it begins to deconvolute only at 100 °C) (Chen, Zhong, Huang, & Pu, 2022).

Starch digestion is the hydrolysis of starch molecules by amylase, which are ultimately broken down into glucose or maltose. In order to further analyse the intrinsic relationship between the crystalline structure and RS, in this study, the details of the complexation and interaction between the double-helix molecule (representing the amorphous region of starch) and human α-amylase were analysed by using molecular docking and dynamics simulation. Single-chain amylose was used as a control to observe starch digestion in the amorphous region.

This study elucidates the intrinsic relationship between the crystalline structure of starch and RS at the molecular level, which will provide an important reference for RS preparation and the study of its formation mechanism.