Microstructure and viscosity of in vitro-digested rye and wheat food products

Understanding rye and wheat digestion is vital for evaluating impacts on nutrient availability and glycaemic responses. This study investigated the disintegration of processed high-fibre rye foods and refined wheat products during simulated intestinal digestion, aiming to link product characteristics with nutrient liberation. The overarching aim was to elucidate how these rye products contribute to the observed benefits in human intervention studies, particularly regarding satiety, weight loss, and metabolism. Analysis included four wholegrain rye products and three refined wheat products, spanning yeast-fermented breads and un-leavened cereal products. Microstructure examination revealed larger, partially intact digesta particles in wholegrain rye products after 120 min of digestion, alongside more aggregated and less degraded starch granules compared to refined wheat bread. Fermented rye bread exhibited greater degradation of subaleurone cell wall fragments than un-fermented rye bread. Viscosity assessments indicated lower viscosity for wheat products than for rye products, with yeast-fermented soft rye bread and rye crispbread showing notably lower viscosity than unfermented rye products. Post-digestion carbohydrate analysis uncovered higher glucose and maltose release during digestion for wheat products. PCA analysis confirmed negative correlations between glucose and maltose release and rye products, characterized by larger post-digestion bolus particles and higher dietary fibre. The elevated cell wall content in rye products acted as a protective barrier for starch granules, mitigating swelling and amylose release, explaining the observed viscosity differences between wheat and rye products and potentially influencing starch digestibility. Consequently, rye products undergo slower and less complete digestion than wheat, aligning with findings from human intervention studies.