Starch gels enriched with phenolics: Effects on paste properties, structure and digestibility

Phenolic compounds affect starch-based gels features and their further hydrolysis with starch digestive enzymes. However, the acidification produced by the addition of phenolics, might be responsible in some extent of the effects reported. The aim was to analyze the effect of different phenolic compounds (benzoic, protocatechuic, vanillic and veratric acid) on microstructure, texture, and digestion of corn starch gels, discriminating between the effect related to pH decrease and that associated to phenolics. Phenolic compounds reduced cooking stability and final gel viscosity, due to the acidic pH, but that effect was not observed at gels of similar pH (around 5.5). At that pH starch gels retained higher amount of phenolics (from 27.70 ± 0.77 for veratric acid to 37.18 ± 3.44 for protocatechuic acid). The effect on starch in vitro digestibility of gels was dependent on the type of phenolic compound, but when comparing at similar pH, all phenolics decreased at least 5% the rate and extent of starch hydrolysis. Higher inhibition against α-amylase was obtained with phenolic compounds with more than one hydroxyl group, like protocatechuic. Overall, phenolic compounds added into starch-based food matrix could modulate the postprandial glucose release when proper pH adjustment was conducted (pH gel > pKa phenolic compound).