Combined crystalline, lamellar and granular structural insights into in vitro digestion rate of native starches

In low moisture foods, such as biscuits, starch supramolecular and granular structures are largely retained, and these govern starch digestibility in such systems. Here, the supramolecular (crystalline, lamellar, and granular) structures of ten different starches were investigated to evaluate how such structures together determine the digestion rate of native starch. In particular, the Spearman correlation analysis revealed that starch digestion rate could be affected by the crystalline type and the granule pores or channels. However, these structural features did not govern the digestion rate in isolation. For instance, starch granules with the same crystalline type could show significantly different digestibility. Hence, the relationship between combinations of multiple structural features and the digestion rate was further investigated through the correlation analysis. Specifically, we found that 1) thinner lamellae caused a lower digestion rate for either A- or B/C type starch; 2) the degree of crystallinity tended to significantly affect the digestion rate of B/C-type starch rather than A-type starch; and 3) the compactness of starch fractals (power law exponent a) was negatively correlated with the digestion rate. The underlying mechanisms were discussed for these correlations. The results could facilitate the strategic selection of starch resources for developing low moisture foods with reduced starch digestion rate (glycaemic index), using combined structural features such as lamella thickness, fractal density and crystallinity.