Short-term stability of soy isoflavones extracts: Sample conservation aspects

Short-term storage stability of soy isoflavones was determined by evaluating the effects of storage duration, temperature, UV-Vis light and vial head space on individual isoflavone concentration. Concentration of isoflavones in ethanol-water extracts and standard solutions stored with temperatures between −20 and 10 °C remains unchanged up to one week. Degradation of malonyl isoflavones is affected by storage duration, temperature, incident UV-Vis light and vial head space. Glucoside isoflavones were not sensitive to the experimental storage conditions. Daidzein and glycitein were the only aglucones sensitive to UV-Vis light. Isoflavones must be kept at temperatures lower than 10 °C and protected from light. Using these conditions, the extracts can be stored up to one week with no significant degradation of isoflavones allowing better planning of routine analysis of large number of samples.