Impact of food processing on rye product properties and their in vitro digestion

Purpose Rye products have been reported to elicit postprandial insulin and glucose responses which may be beneficial for prevention of type-2 diabetes. However, mechanisms underlying variations in responses related to processing techniques are not fully understood. Methods Five differently processed rye products (sour-dough-fermented bread, fermented and unfermented crispbread, extrusion-cooked rye, and porridge) and refined wheat bread were characterised. Two in vitro methods, a dynamic method simulating digestion in the stomach and small intestine and a static method, simulating conditions in the stomach were used to determine viscosity development, structural changes and release of glucose during digestion. Results Structural and compositional differences induced by processing influenced product digestion. Gastric disintegration and digesta particle size were related to characteristics of the starch/protein matrix, while digesta viscosity was reduced due to fibre degradation during fermentation. More cohesive boluses were associated with slower glucose release. Sourdough fermentation increased amylose leakage and appeared to inhibit starch hydrolysis despite low digesta viscosity and rapid disintegration. Conclusions The net release of glucose during digestion of foods is determined by several factors which may vary in their importance depending on product specific properties.