Assessing Chemical Form of Calcium in Wheat, Spinach, and Kale

Spinach, wheat and kale represent a broad range in absorption of calcium from foods (5–40%). These plants were intrinsically labeled with ⁴⁵Ca and examined for ⁴⁵Ca solubility characteristics, including specific enzyme treatments, subcellular distribution, and in vitro bioa-vailability. Solubility was <2% for spinach, ～40% for wheat and 70% for kale, depending on the solvent. Solubility paralleled the in vitro⁴⁵Ca bioavailability results of 0.3±0.l%, 26.4±5.2%, and 76.3 ±1.2% for these three plant foods. Spinach calcium exists largely as calcium oxalate which is not easily dissociated. Phytase treatment of wheat indicated that a major portion of calcium was bound to phytate. Knowledge of the chemical form of calcium in plants can help in designing processing procedures to improve calcium absorption.