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Slowly digestible starch is recognized to contribute to the reduction of the risk of common chronic diet-related metabolic diseases. Several studies, including at our institute, have shown that increasing flour particle size slows down the starch digestion rate. However, the presence of large particles (>120 µm) can result in a poor quality of the final product. In this scenario, we hypothesised that a fine flour with a compact structure, such as that from maize hard endosperm, would be digested more slowly. The aim of this work was to study the effect of the compactness of maize flour endosperm on starch digestion. Both fine (126 µm) particles from hard and soft maize endosperm were obtained by adjusting the break passages until particles with similar size but different compactness were observed by SEM. Sections of flour particles were assessed for microstructure, and starch fine structure, crystalline polymorphism, thermal transitions, particle size; and <i>in vitro</i> starch hydrolysis was also analysed. Results suggest that not only particle size but also particle compactness are fundamental factors to control starch digestion rate. Both proteins and starch contribute to the hard endosperm compactness of conventional maize. As for the starch, amylose and amylopectin fine structure can improve the starch assembly at higher levels, slowing the starch digestion. This work is towards the larger goal of identifying appropriate starchy matrices to produce foods with a slow digestion property.