Abstract
In the previous paper, it was indicated that a water-extracted soybean protein heated at high temperature in minutes is efficiently utilized as protein source by rats. Since this protein fraction contains 0.49-0.52% of phytin-phosphorus (64-68% of total phosphorus), the present paper is concerning with the availability of phytin-phosphorus of soybean.
The low phytin protein was prepared by precipitation of Ca phytate at pH 8.5 from the aqueous solution of the soybean protein and the following spray drying. When fed to young rats for 29 days the diet of the low phytin soybean protein supplemented with Na phytate, Ca phytate and inorganic phosphorus at a total phosphorus level of 0.25% of the diet (0.20% of phytic acid phosphorus), respectively, the phytic acid phosphorus was inferior to inorganic phosphorus for bone calcification, namely 78 or 85% in weight of femur ash. When the phytin-phosphorus diet was supplemented with a small amount of inorganic phosphorus (0.06%), the bone calcification was improved.
In the absence of vitamin D, the availability of phytic acid phosphorus for the bone formation was decreased, but also that of inorganic phosphorus in the lesser degree and the phytase activity of the small intestine were almost equally reduced from 2.5 and 2.8mg (in the presence of vitamin D) to 1.9 and 1.7mg P/g/30min.
