Role of particle size in modulating starch digestibility and textural properties in a rye bread model system.

In cereal products, the use of flour containing clusters of intact cells has been indicated as a potential strategy to decrease starch digestion. Rye possesses more uniform and thicker cell walls than wheat but its protective effect against starch digestion has not been elucidated. In this study, rye flours with three different particle sizes, large (LF) (∼1700 µm), medium (MF) (∼1200 µm), and small (SF) (∼350 µm), were used to produce model bread. The textural properties of these breads were analysed using Textural Profile Analysis (TPA). The starch digestibility of both the flour and the bread was measured using Englyst's method, while the presence of intact cell clusters was examined using Confocal Laser Scanning Microscopy (CLSM). Additionally, the disintegration of bread digesta during simulated digestion was assessed through image analysis. CLSM micrographs revealed that bread made with MF and LF retained clusters of intact cells after processing, whereas bread made with SF showed damaged cell walls. Starch digestibility in LF and MF was lower (p ≤ 0.05) than that in SF. Bread produced with MF and LF exhibited the least (p ≤ 0.05) cohesive and resilient texture, disintegrated more during digestion, and exhibited higher starch digestibility (p ≤ 0.05) than bread made with SF. These results highlight the central role of bread texture on in vitro starch digestibility.

Monitoring the effect of cell wall integrity in modulating the starch digestibility of durum wheat during different steps of bread making.

Reduction of starch digestibility in starchy foods is beneficial for lowering the risks for major non-communicable diseases. Preserving cell integrity is known to delay starch digestibility in flour but its effect in bread is not clear. In this study, the effect of increasing particle size on in vitro starch digestibility of durum wheat flour, dough, and bread was investigated. Cell integrity was retained during bread processing for medium (1000 µm-1800 µm), and large (>1800 µm) flour, whereas in small one cell walls were mostly damaged (<350 µm). In vitro starch digestibility of flour decreased increasing particle size, but no difference was found in dough. In bread, instead, a modest decrease of starch digestibility for the bread made by large particle was observed, likely due to its dense structure. In conclusion, a high particle size could limit starch digestibility in durum wheat flour but not in bread.