Multiscale investigations of potato and wheat starch interactions with water in the absence or presence of sodium and calcium ions

Abstract

Starch interactions with water form the basis for its functional properties. Potato starch (PS) and wheat starch (WS) functionality are notably different, and largely attributed to the presence of negatively-charged phosphate monoester groups in the former and absence of these groups in the latter. In this study, sodium and calcium chloride salts were added to PS- or WS-water model systems as their cations interact with the charges of phosphate groups when present. Time domain proton nuclear magnetic resonance (TD ¹H NMR) findings showed that PS exhibits higher mobility of water protons (higher T₂ relaxation time) than WS. Upon cation addition, proton mobility is reduced only in PS illustrating that cation interactions with charged phosphate groups lead to stronger starch-water interactions and greater confinement of water protons in starch granules. Alongside PSs’ reduced swelling power and leaching of carbohydrates, it is suggested that cation interactions with PS hamper its capacity to form hydrogen bonds with water, thereby limiting swelling. In WS, cations can only interact with the hydroxyl groups of starch and exhibit a weaker impact on proton mobility, swelling, and pasting. These findings indicate that phosphate groups in PS considerably impact its functionality by altering its molecular-level interactions with water.