Citric acid esterification of unripe plantain flour: Physicochemical properties and starch digestibility

Resistant starch (RS) from raw plantain flour (RPF) is destroyed after cooking, thus losing its nutraceutical benefits. The objective of this work was to obtain esterified flours from RPF and evaluate starch fractions, and physicochemical, structural, and morphological properties. RPF was esterified with citric acid (40 g/100 g dry flour, pH 3.5) at 140°C (CAT-PF) for 7 h after conditioning treatment. As a complementary study, the effect of cooking on the starch fractions of flours was evaluated. RPF and heat-treated plantain flour (HT-PF) that had not been treated with citric acid were used as controls. The cooking for 20 min of RPF and HT-PF decreased the RS content compared with its uncooked counterpart, but RS content of CAT-PF was not modified. The citric acid treatment caused a decrease in gelatinization temperatures and enthalpies. FTIR spectroscopy and XRD analyses confirmed the incorporation of citric acid groups in the starch structure through changes in the FTIR spectra and crystallinity patterns. Granular aggregates were observed in CAT-PF or HT-PF. CAT-PF with high RS content and cooking stability could be used as an ingredient in the formulation of nutraceutical foods.