Does the presence of fibres affect the microstructure and in vitro starch digestibility of commercial Italian pasta?

Dry pasta is a staple food in many countries of the world and it is traditionally made of durum wheat semolina. The aim of this study was to evaluate the impact of pasta composition on microstructure, water absorption and mobility during cooking and nutritional properties of two commercial spaghetti made of durum wheat semolina (S) and whole durum wheat semolina (WS). Scanning Electron Microscopy (SEM) revealed no significant microstructural differences between the uncooked pasta samples, whereas the presence of fibre altered the integrity of the protein network in the cooked samples. Moreover, the water absorption during cooking and the water mobility at molecular level were investigated as weight increase and by low-resolution 1H NMR experiments, respectively. Compared to durum wheat spaghetti, the presence of fibre increased the water absorption while decreased the proton relaxation times 1H T2 and 1H T1 indicating an increased degree of water-polymers interaction. Lastly, the rate of starch hydrolysis, evaluated by means of in vitro methods, increased in presence of fibre, resulting in higher RDS and estimated Glycemic Index (eGI) for whole durum wheat spaghetti compared to the traditional ones. These findings were quite unexpected