Effect of Citric Acid and Sodium Trimetaphosphate Induced Crosslinking on Functional, Rheological, Structural, and Thermal Properties of Buckwheat Starch

Abstract

The present study utilizes citric acid (CA, 12-60% of dry starch) and sodium trimetaphosphate (STMP, 6-30% of dry starch) to crosslink buckwheat starch. The major morphological changes are observed for CAinduced crosslinking, which erodes the polygonal and irregular shaped granules surface leading to formation of indentation and disappearance of pores. FTIR analysis confirms CA crosslinking, which introduces a new peak at 1720 cm −1 (stretching vibration of C═O). XRD pattern reveals both crosslinkers disrupt the crystalline region of native granules leading to reduction in crystallinity index. These changes detrimentally affect the solubility and swelling power even at higher temperature (95 °C). As a result, the pasting curve gets flattened and very poor gel is formed. The crosslinked starch gels are highly flowable, have low yield stress, and show shear thinning behavior. The thermal analysis shows that CA starches gelatinize at lower temperatures due to poor crystalline structure and require lower energy. Thermogravimetric analysis shows crosslinked starches have higher residual mass (10.20-25.17%) at 450 °C compared to native (8.66%). Conclusively, as the concentration of crosslinkers increases, the properties of BS undergo more pronounced changes, resulting in severe alterations in its functional, rheological, and thermal properties at higher concentrations.