Isoflavone levels and the effect of processing on the content of isoflavones during the preparation of soymilk and tofu

Abstract

Soybeans and soy foods are abundant sources of isoflavones. The initial objective of this study was to develop a reversed phase high performance liquid chromatography method for the quantification of isoflavones in soy products. Different extraction and processing methods are used for the preparation of soymilk and the effect of processing on the content of isoflavones in soymilk was further determined. Hot grinding caused a higher extraction of isoflavones than cold grinding, while a direct or indirect UHT process did not cause a difference in the content of isoflavones in soymilk prepared. The effect of different coagulants on the retention of isoflavones in the tofu prepared showed calcium sulphate as producing a firm tofu with better textural properties and it retained higher amounts of isoflavones than many of the other coagulants of study. The HPLC method developed proved a simple, rapid and reproducible method for the precise quantification of isoflavones in soy-based products.