Spaghetti ai neutroni: Investigating the nanostructure of (gluten-free) pasta

Researchers use neutrons and X-rays to look into the structure of spaghetti at the nanometre scale, comparing the effect of cooking and salt in gluten-free and gluten-containing pasta

Most people would probably agree that today’s gluten-free pasta options are generally less appealing than the gluten-containing ones. The good news is that researchers are working to improve the mouthfeel of gluten-free spaghetti. Results have just been published in a special issue of the journal Food Hydrocolloids devoted to the Northern Lights Food Conference.

Researchers used both neutrons and X-rays to look into the nanostructure of spaghetti, comparing gluten-free and gluten-containing versions. Small-angle X-ray scattering experiments performed at the Diamond Light Source (UK) allowed researchers to compare raw spaghetti with spaghetti boiled for a variety of cooking times and with different amounts of salt. Adding salt helps preserve the structure of the spaghetti – but only when it is used at the right concentration and the pasta is cooked for the right amount of time.

Neutron experiments were conducted both at the ILL and at ISIS Neutron and Muon source (UK). In both cases, small-angle neutron scattering (SANS) was combined with contrast variation techniques: isotopes of the same element have similar chemical properties but may scatter neutrons in very different ways. This is the case for hydrogen (H) and deuterium (D). By cooking the pasta in different mixtures of normal (H₂O) and heavy (D₂O) water, researchers could make samples that each highlighted a different component of interest, with others appearing invisible to the neutron beam. In this way they could separate the effect of cooking on the starches and the gluten, the two main components of ‘normal’ pasta.

At the ILL, the measurements were performed using the SANS instrument D11. “The samples were prepared in the chemistry lab next to D11, which during those days somehow resembled a kitchen » recalls D11 instrument scientist Ralph Shweins. « Pasta smell was in the air, and the pasta was carefully and accurately prepared by the scientists. The experiment was exciting, something exceptional, it is very fascinating to see what neutrons can contribute to understanding food better. »

After cooking, the samples were cut into small pieces and confined in sample holders. The analysis of the data has shown that the starch granules swell upon cooking, and tend to disperse, whereas the gluten proteins (more like a stringy mesh) become insoluble and coagulate into a network. This has the effect of trapping the starch and retaining the structure of the pasta.

In the gluten-free spaghetti, this network is missing, which means the starch granules can over-swell. This is why gluten-free pasta can fall apart or become sticky during cooking, especially if overcooked.

“Our findings indicate that regular pasta shows a higher tolerance, or better structural resistance, to non-ideal cooking conditions such as too long cooking time or excess amount of salt in the cooking water,” says Andrea Scotti from Lund University, one of the authors of the paper.

The team plans to continue exploiting the potential of neutron and X-ray scattering. Next steps include studying different pasta varieties, as well as replicating what happens to the nanostructure of pasta once it’s inside the stomach. Stay tuned!

Acknowledgements: this web article in based on the text by Rosie De Lune published on the ISIS website.