Evaluation of potential mechanisms by which dietary fibre additions reduce the predicted glycaemic index of fresh pastas

A range of commercially available dietary fibres (DFs), representing both insoluble and soluble forms, were used in the production of pasta. Addition of fibre was at a range of levels (2.5-10%). The potential glycaemic index of these pastas was then evaluated using an in vitro model system to determine starch digestibility and sugar release. Scanning electron microscopy was used to relate structural properties of the pasta to starch degradation. The resulting predicted glycaemic indexes illustrated that the inclusion of DFs into pasta can reduce the glycaemic index of an already low GI food by up to 40%. As such, compared to the predicted glycaemic index value for the control fresh pasta (GI = 45), inclusion of pea fibre, guar gum and locust bean gum yielded pasta with GI values of 39.2, 37.9 and 37 respectively. Thus the type of dietary fibre used was important in the rate of starch digestion observed during the in vitro process. Equally, the level of fibre inclusion was of importance with an inclusion rate of 2.5% generally resulting in pasta with a predictive GI of 42.1, whereas an inclusion of 10% yielded pasta with a GI value of 37.2. Such reductions could be achieved through a number of possible mechanisms including antagonistic and synergistic relationships existing between DF's and other food components, the effect of DF's in entrapping pasta particles and thus inhibiting starch degradation, and the restriction of water movement during the cooking of pasta products, thus indicating that starch swelling is impaired.