Mechanism of reduction in starch digestion rate of Durum Wheat by protein

Abstract

The aim of the project is to explore the mechanism of durum wheat proteins in slowing starch digestion; this reduction in digestion rate is nutritionally advantageous. The grains of three commercial durum wheat varieties (Jandaroi, Caparoi and Yawa) were employed, from which a range of pasta-derived cooked substrates were prepared: semolina (SE), whole pasta (spaghetti) (WP), powdered pasta (PP) and extracted starch (ST). SE contains inherent protein components; WP has an intact compact structure and gluten network formed by kneading and extruding the SE proteins; PP was ground from WP, thus breaking up the intact compact structure while the gluten network remained intact; and ST was extracted from SE with removal of proteins. To understand how pasta compact structure and proteins influence starch digestion, all these starch-containing samples with different protein composition and structure were subjected to in vitro digestion with various combinations of treatments mimicking gastric conditions with acid and pepsin, before the starch was digested with porcine α-amylase or pancreatin. After plotting the percentage of starch digested vs. time, first-order kinetics characterization through logarithm-of-slope analysis and morphological characterization by confocal microscopy were combined to reveal how the pasta compact structure and gluten network together slow starch digestion rate. Digested samples were collected at different times to characterize the weight distributions of branched starch molecules (wbr (logR h ), R h being hydrodynamic radius) using size-exclusion chromatography (SEC, also termed GPC). These distributions, together with the measured activity of α-amylase in the digestive solution, were used to explore the role that the compact structure and proteins in pasta play in retarding the evolution of starch molecular structure during digestion. Gluten powder (GP) extracted from SE was cooked and centrifuged to separate supernatant from gluten as a pellet, followed by the addition of α-amylase, to characterize to what extent α-amylase interacted with wheat proteins by measuring the activity of α-amylase, to elucidate if the protein components are capable of reducing enzymatic II activity; the analytical technique used was high performance liquid chromatography-mass spectrometry (LC-MS).The results showed that ST and SE were digested following simple first-order kinetics, while WP and PP followed two sequential first-order steps. The rate coefficients for these various steps were altered by pepsin hydrolysis. Confocal microscopy revealed that, following cooking, starch granules were completely swollen for ST, SE and PP samples. In WP, the granules were completely swollen in the external regions, partially swollen in the intermediate region and almost intact in the WP strand center. Gluten entrapment accounts for the sequential kinetic steps in the digestion of pasta starch; the compact microstructure of pasta also reduces digestion rates. A reduced activity of porcine α-amylase and retarded dig...

Effect of variation in starch B‐granule content in durum wheat on technological properties and in vitro starch digestion of spaghetti

“…Examination of the starch digestibility in the uncooked pasta may reveal differences due to starch granule size. Given the importance of the gluten matrix in influencing starch digestion (Zou, 2016 and references therein), it is apparent that removing the protein influence from the genotypes in the pasta system and replacing with the same gluten, might be a better way to assess the different starch granule distributions. In addition, proteins present on the surface of starch granules may interfere with enzymic hydrolysis (Singh et al, 2010) and these may have also accounted for effects observed.…”