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Physicochemical properties and starch digestibility of modified tapioca starch using various citric acid concentrations (10, 30, and 50 g/100 g dry starch) and heating temperatures (100, 120, and 140 °C for 5 h) are investigated. It is found that the degree of esterification increases with increasing dose of citric acid and heating temperature. Differential scanning calorimetry shows that citrate starch samples exposed to high acid dose (30 g/100 g citric acid) and temperature (120 °C) are resistant to gelatinization. In addition, transitional enthalpy also decreases with increasing concentration and temperature. The microstructure of esterified starch is observed to have agglomerated granules, with corrosions/fissures and small overlapping layers on the surfaces, which are observed in all modified samples. Citric acid esterification of tapioca starch provided advantages in terms of the increase resistant starch content and slow digestion rate when compared to native starch.

Flour and starch isolated from the tubers of Scirpus grossus were investigated for their physicochemical properties and starch digestibility. The flour was extracted using two different processes namely peeled and unpeeled processes. Proximate analysis revealed that the flours from both processes contain considerably high total starch, more than 80%, which indicate their potential use as starchy foods. The amylose content of the flours and starches ranged from 29 to 32%. Starch granules of S. grossus were oval in shape with smooth surface and small diameters ranging from 6 to 15 μm. All samples exhibited high swelling pasting behaviors with pasting temperatures ranging from 78 to 79 °C, indicating the strong bonding forces within the granule interiors. Differential scanning calorimetry (DSC) results suggested that the samples gelatinized at temperatures ranging from 71 to 81 °C. In vitro starch digestion assay found that all samples provided the estimated glycaemic index (GI) values of approximately 55 or less. Highlights•The flour and starch of Scirpus grossus have the potential to be used as starchy foods.•Their functional properties have not yet been investigated.•This study determined their physicochemical properties.•The findings here suggested that it could be used in low GI food products.

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