Determination of unusual soya and non-soya phytoestrogen sources in beer, fish products and other foods

Abstract

Fish and fish products (14 samples), Indian foods and meals (10 samples), spices (30 samples) and beers (10 samples) were analysed for their phytoestrogen content, and a number of significant non-soya sources of dietary phytoestrogens were identified. No isoflavones were detected in unprocessed, farmed or ocean fish, but some samples of processed fish products contained soya isoflavones, which are assumed to come from coatings or protein addition. Additionally, some processed fish products contained, genistein glycocongugates not derived from soya. Genistein was detected in Indian meals such that, for example, a single portion of a vindalooo curry contained 11 mg genistein. The origin was most likely from the spices used, since the analysis of curry powders, chilli powder, crushed red chillies, garam masala and tandoori powder revealed that some contained genistein at more than 100 mg kg−1. Cumin was the most likely source material, although not all individual samples of cumin tested contained high levels of genistein. Prenylnaringenin phytoestrogens were determined in UK hop-based beers at mean concentrations of 0.21 mg−1 6-prenylnaringenin and 0.06 mg−1 8-prenylnaringenin. The beers also contained traces of daidzein, genistein and biochanin A. The significance of ‘hidden soya’ in processed foods and these non-soya sources of phytoestrogens is that UK dietary intake of phytoestrogens must be assumed to be higher than estimated previously and that some sources of phytoestrogens remain poorly characterized.