抄録
Utilization and requirement of soy protein isolate (SPI) and SPI-rice combination were examined in twenty-five female students. After 1 day on protein-free diet, each subject received a low-protein diet for 10 days. The protein sources were SPI for ten subjects and SPI-rice combination, in which the ratio of two proteins was 6:4, for fifteen subjects. The nitrogen intakes were about 45, 65 and 85mg/kg in both the two series of experiments. Energy intake was at an approximate maintenance level of 36.1±3.0 kcal/kg. Apparent nitrogen balance improved with increase in nitrogen intake. The regression equations between nitrogen intake (X, mg/kg) and balance (Y, mg/kg) are shown in the following:
SPI: Y=0.411X-40.8 (n=10, r=0.812)
SPI and rice protein: Y=0.392X-32.7 (n=15, r=0.739) From the above equations, the maintenance intakes of SPI and SPI-rice combination for an apparent nitrogen equilibrium were calculated to be 99 and 83 mg N/kg, respectively. Digestibilities were 98.2±5.0% for SPI and 93.1 ±6.10 for SPI-rice combination. The NPUs of SPI at intake levels of 40, 60 and 80mg N/kg were 47±24 (n=4), 49 (n=2) and 44±3 (n=4), respectively. The NPUs of SPI and rice mixed protein at intake levels of 45, 70 and 90 mg N/kg were 67±13 (n=5), 51±7 (n=5) and 54±12 (n=5), respectively. It was concluded from the present study that both SPI and the SPI-rice combination had a high nutritive efficiency comparable with that of egg protein.
