Influence of Phytate Removal and Structural Modification on the Calcium-binding Properties of Soybean Globulins.

The calcium-binding properties of soybean globulins that have been deamidated or enzymatically hydrolyzed after the removal of phytate were physicochemically investigated. The level of calcium was reduced from 0.32% to 0.013% and that of phosphorus was reduced from 1.1% to 0.050% by treating with cation- and anion-exchange resins. The calcium-binding properties of soybean globulins were described by the Langmuir equation, the maximum amount of bound calcium (N) and the affinity parameter for calcium (K) being obtained for each sample. The value of N was decreased by the removal of phytate, while the deamidation caused the value of N to increase. As hydrolysis proceeded, the value of N increased to a degree of hydrolysis of 32%, and then decreased. Based on this result, there seems to be an optimum molecular weight of hydrolyzed soybean globulins for the amount of bound calcium. In addition, the value of K for every soybean globulin sample was much lower than that of phytic acid, indicating that the globulins had proper calcium-binding properties for calcium absorption in the small intestine.