Structural barriers governing starch digestibility in intact highland barley cells: A closer insight from cell wall and protein matrix.

The endosperm cell structure plays an important role in starch digestion. This study aimed to evaluate the effects of the structural properties of the cell wall and protein matrix on starch digestibility in intact cells isolated from the endosperm of highland barley. Damaged cells with different degree of cell wall degradation were obtained by controlling the time of β-glucanase hydrolysis of isolated cells. Intact cells exhibited the lowest starch digestibility (61.80 %) and gelatinization enthalpy change (3.55 J/g). As the degree of β-glucanase hydrolysis increased, the starch digestibility of damaged cells markedly increased and was close to that of mechanically crushed flour. Penetration of amylase-sized fluorescent probes showed that the probes barely penetrated the raw and cooked cell walls, indicating that the cell wall strongly blocked the contact between amylase and starch. Additionally, the compound network formed by the protein matrix and expanded starch hindered probe diffusion. However, the starches in the cells with the greatest cell wall loss were fully digested after 6 h of digestion. Therefore, the cell wall, an effective structural barrier to amylase, mainly limits starch digestibility, whereas the protein matrix/network acts as a secondary barrier. This study provides new insights into the processing of slow-digested cereals.