A recent increase in adverse effects on the reproductive capabilities of animals and humans has been observed. Reduced sperm count and increased testicular and breast cancer are of particular concern. The cause of these observations is likely the disruption of the endocrine system. One such endocrine disruptor is genistein, abundant in soy and a common addition to everyday foods such as bread and tofu. It has been shown that isoflavone levels alter throughout the bread making process, with the total amount decreasing and inter-conversion between different isoflavones as well as different glycoside and aglycone forms occurring. A possible explanation for this may be the metabolic activity of Saccharomyces cerevisiae or bacteria in the case of sour dough, causing modification or the breakdown of these compounds. This may result in the health effects of baked bread being not simply a sum of the health effects of the breads ingredients. Yeast metabolism of these compounds has not been looked at before and could be a significant factor unaccounted for. Isoflavone transformations throughout food preparation and processing can play a large role in the context of functional foods as the isoflavone aglycone is more bioactive and bioavailable than the naturally occurring sugar conjugate, which is responsible for the pharmacological activity and thus the changes to health that may occur. While release of the aglycones during food manufacturing processes increases the functionality of isoflavone containing fermented foods, the potential metabolic inter-conversion of isoflavones is likely a far more important factor, as different isoflavones have different levels of pharmacological activity, while the microflora in our digestive tract are also capable of releasing the aglycone. For this reason bacterial metabolic conversion from an isoflavone with higher estrogenicity (e.g. genistein; EQ = 2.6 x 10-4) to lower estrogenicity (e.g. daidzein; EQ = 1.1 x 10-4) during the food manufacturing process might reduce functionality. An example of this could be women eating soy bread as a post-menopausal pseudo-hormone replacement but not receiving as much benefit from it as initially thought. My project involves determining what metabolism or interconversion of isoflavones occurs during the bread making process. This helps lead to a better understanding of the level of estrogenic effects caused by the addition of soy to bread.