Cholesterol-lowering effect of soybean protein isolate in chicks is partly lost by microbial protease digestion.

Effects of soybean protein isolate (SPI) and its enzymatic hydrolysate (HYS) on the serum and liver cholesterol concentrations were compared in chicks. Seven-day-old chicks were fed the experimental diets containing 0.5% cholesterol for 10 days. Various nitrogen sources isonitogenously replaced SPI in the control diet (20% crude protein). HYS treated with endo-type protease alone (HYS-A) or in combination with exo-type protease (HYS-B) for 5h did not cause any changes in the serum and liver cholesterol concentrations as compared with SPI. On the other hand, HSY-C treated with endo- and exo-type proteases for 24h lowered the HDL-cholesterol concentrations and the ratio of HDL-cholesterol to total cholesterol concentrations in the serum, but increased the liver cholesterol concentrations. Digested soluble fraction after removing the sediment from HYS-C and amino acid mixture simulating SPI further increased the serum total cholesterol and liver cholesterol concentrations. These results indicate that the conformation of protein plays an important role in the cholesterol-lowering effect of SPI.

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