Insights into the effect mechanism of acidic pH condition on the in vitro starch digestion of black highland barley semi-dried noodles.

In this study, black highland barley semi-dried noodles (BHBSNs) were adjusted to acidic pH (5.0, 4.5, 4.0) with an acidity regulator (monosodium fumarate) for obtaining low glycemic index (GI) BHBSNs, and the changes in the in vitro starch digestion, free phenolic content, and α-amylase activity in BHBSNs were investigated. The estimated glycemic index (eGI) of BHBSNs decreased from 59.23 to 52.59, 53.89 and 53.61, respectively, as the pH was adjusted from 6.0 to 5.0, 4.5, 4.0. As the pH of BHBSNs decreased, the equilibrium hydrolysis (C ∞) decreased, and kinetic coefficient (k) decreased and then increased. Compared to the control, the pH of the digestive fluid decreased during digestion with decreasing pH, and the α-amylase inhibition of BHBSNs with pH 5.0, 4.5, and 4.0 increased by 56.54 %, 75.18 %, and 107.98 %, respectively. In addition, as the pH of BHBSNs decreased, the free phenolic content and the content of released phenolics during digestion increased. Pearson correlations analysis showed that the increase in α-amylase inhibition and phenolic release during digestion induced by acidic pH was negatively correlated with the eGI and C ∞ of BHBSNs. This study indicated that acidic pH condition could modulate starch digestion for preparing low GI BHBSNs. [Display omitted] • Acidic pH reduced starch digestion and eGI of BHBSNs. • The pH in the digestive fluid of acidic BHBSNs was lower than the control. • Acidic pH caused an increase in the phenolics released during digestion of BHBSNs. • The lower pH and the released phenolics inhibited the activity of α-amylase. [ABSTRACT FROM AUTHOR]