Can Manipulation of Durum Wheat Amylose Content Reduce the Glycaemic Index of Spaghetti?

Resistant starch (RS) in foods has positive benefits for potentially alleviating lifestyle
diseases. RS is correlated positively with starch amylose content. This study aimed to see what
level of amylose in durum wheat is needed to lower pasta GI. The silencing of starch synthases
IIa (SSIIa) and starch branching enzymes IIa (SBEIIa), key genes involved in starch biosynthesis,
in durum wheat cultivar Svevo was performed and spaghetti was prepared and evaluated. The SSIIa
and SBEIIa mutants have a 28% and 74% increase in amylose and a 2.8- and 35-fold increase in RS,
respectively. Cooked pasta was softer, with higher cooking loss but lower stickiness compared to
Svevo spaghetti, and with acceptable appearance and colour. In vitro starch digestion extent (area
under the digestion curve) was decreased in both mutants, but much more in SBEIIa, while in vivo
GI was only significantly reduced from 50 to 38 in SBEIIa. This is the first study of the glycaemic
response of spaghetti prepared from SBEIIa and SSIIa durum wheat mutants. Overall pasta quality
was acceptable in both mutants but the SBEIIa mutation provides a clear glycaemic benefit and would
be much more appealing than wholemeal spaghetti. We suggest a minimum RS content in spaghetti
of ~7% is needed to lower GI which corresponded to an amylose content of ~58%.