New analytical techniques for soy phytochemicals: Saponins and isoflavones

Soy isoflavones and saponins are two major classes of health promoting phytochemicals in soybeans and soy products. An high-performance liquid chromatography/evaporative light scattering detection (HPLC/ELSD) method was developed to determine natural forms of soyasaponin Bs with (alphag, betag, betaa, gammag, gammaa) and without (V, I, II, III, IV) 2,3-dihydro-2,5-dihydroxy-6-methyl-4 H-pyran-4-one (DDMP) in soybean. The coefficient of variance of intra-day assays was < 9.51%, and that of inter-day assays was < 10.91%. The soyasaponin I was used as external standard for quantification of all soyasaponins, because it was established that their ELSD signal responses were essentially the same under the specific operating conditions. The extraction conditions were optimized and the extract storage conditions were established for analysis of soyasaponin Bs in their natural state.; A new procedure for simultaneous determination of isoflavones and soyasaponin Bs in soybeans using HPLC/UV/ELSD has been developed. This method has quantified twelve isoflavones, three non-DDMP soyasaponin Bs (V, I, and II) and five DDMP (2,3-dihydro-2,5-dihydroxy-6-methyl-4H-pyran-4-one) soyasaponin Bs (alphag, betag, betaa, gammag, and gammaa). Sample preparation for this method is unique and required significantly less time than previously published methods.; The mass balance of saponins during processing of soy protein isolates (SPIs) was established and the effects of precipitating and washing (P/W) temperatures (0°C, 10°C, 25°C, 40°C, and 50°C) on the retention of isoflavones and saponins were investigated also. Isoflavones and saponins were measured by a HPLC/UV/ELSD method. It was found that about 41% of total saponins in soy flour (SF) remained in SPIs during processing, while 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 SPIs when P/W was performed at 50°C. However, lowering the P/W temperature improved the isoflavone retention significantly. As much as 40% of total isoflavones can be retained in SPI, when P/W was conducted at 25°C, 10°C, or 0°C. (Abstract shortened by UMI.)...