production differences between dried pasta and fresh pasta. It explained that the production mechanism used to make dried pasta also adds something to the pasta that decreases the GI
An attempt at a brief and hopefully vaguely correct explanation
Extreme temperatures (such as cooking in boiling water) modifies the structure of some of the starch molecules in carbohydrates. This makes them more digestible and hence will raise BG levels. This is is called gelatinisaton.
When pasta is made in a machine the process of extrusion produces a coating on the pasta. This makes the starch less digestible ( and therfore lower gi) This applies to shapes like spaghetti and tagiatelli but less so for flat shapes like lasagna, so two pastas, even when made with the same flour, can have very different gis.
Hand rolled and cut pasta also doesn't go through the same process so tends to be higher gi.
Cooking for too long will destroy the protective coating, increase the gelatinisation so
pasta is only low gi if it is cooked al dente.
If the pasta is cooked then cooled a process called retrogradation occurs , the starch returns to its former structure and is again less digestible , some of the starch is resistant (as it was before processing and cooking).
Cold al dente pasta is therefore lower gi.
Researchers have found how to manufacture, resistant starch and make it (at least partially) heat stable . This resistant starch is put into products like Dreamfields pasta so they advertise it as having less available starch. However, even resistant stach needs to be cooked al dente as it will become more gelatinised and more digesitble if cooked too long.
So, homemade pasta is likely to higher gi than bought dried pasta. If you could buy commercial resitant starch and incorporate it, then it shoulld work in the same way as Dreamfields.
Added:
I've just found a resistant starche sold directly to consumers. Its called Hi Maize and was developed in Australia. Apparently it can replace 25-30% of the flour in 'baked goods' ( I assume pasta also) . The bad news is I've so far only found it on sale in the US and Australia.(though its used here in some Breads and cereals )