Retention of isoflavones and saponins during the processing of soy protein isolates

The mass balance of saponins during processing of soy protein isolates (SPI) was established, and the effects of precipitating and washing (P/W) temperatures (0, 10, 25, 40, and 50°C) on the retention of isoflavones and saponins were investigated in this study. About 41% of total saponins in soy flour (SF) were found to remain in SPI during processing, whereas 42% remained unextracted in the solid waste. None was detected in the whey or wash water. The study also revealed that only about 27% of total isoflavones from SF remained in the final SPI when P/W was performed at 50°C. As much as 40% of the total isoflavones could be retained in SPI when P/W was conducted at 25, 10, or 0°C. When the P/W temperature was 50°C, the percentages of total isoflavones lost during extraction, precipitation, and washing were 28, 22, and 6%, respectively. When the temperature was changed to 0°C, the percentages of isoflavones lost during extraction, precipitation, and washing were 28, 11, and 5%, respectively. The P/W temperatures did not affect the distribution of saponins in different streams during the processing of SPI. Lowering the P/W temperature did not significantly lower the protein content in SPI unless the temperature was reduced to 0°C.