Structure-digestibility relationship from noodles based on organocatalytically esterified regular and waxy corn starch obtained by reactive extrusion using sodium propionate

Health-promoting starchy noodles (spaghetti-type pastas) were manufactured from organocatalytically esterified regular and waxy corn starches. The noodles were obtained via reactive extrusion (REx) using sodium propionate (NaPro) as a precursor of propionic acid (PAc – short-chain fatty acid, SCFA) and tartaric acid (TAc) as a food-grade green organocatalyst. The values of degree of substitution (DS) determined by titration varied between 0.78 and 1.22. Solid-state 13C CP MAS NMR spectra evidenced that all Pro-containing noodle systems were propionylated, regardless of the use of the organocatalyst. However, the determination of DS values could not be adequately calculated from the solid-state 13C CP MAS NMR spectra, since the organocatalyst and the unreacted Pro inevitably remained embedded in the REx-processed noodle systems. The results also suggest that amylose (amorphous regions of starch) is more susceptible to being esterified by Pro than amylopectin (crystalline regions of starch). Greater thermal resistance, more compact morphologies and higher crystallinity values were evidenced by increasing the DS values. The long-range ordered structure was dominated by the A-type crystalline structure for all noodle systems studied. Notwithstanding, V-type structure was also evidenced, and related to short-range ordered crystalline structures. Organocatalytically propionylated corn starch-based noodle systems had lower free Pro values compared to non-organocatalyzed propionylated corn starch-based noodle systems upon pancreatic digestion, thus confirming the positive effect of the use of organocatalyst for the esterification of Pro onto starch. All propionylated corn starch-based noodle systems showed slower starch digestibility, regardless of amylose content.