Abstract
Estrogenic isoflavones were found, in the 1940s, to disrupt ewe reproduction and were identified in soy-consumers’ urine in 1982. This led to controversy about their safety, often supported by current Asian diet measurements, but not by historical data. Traditional Asian recipes of soy were tested while assaying soy glycosilated isoflavones. As these compounds are water-soluble, their concentration is reduced by soaking. Pre-cooking or simmering time-dependently reduces the isoflavone:protein ratio in Tofu. Cooking soy-juice for 15 or 60min decreases the isoflavone:protein ratios in Tofu from 6.90 to 3.57 and 1.80, respectively (p<0.001). Traditional Tempeh contains only 18.07% of the original soybean isoflavones (p<0.001). Soy-juice isoflavones were reduced by ultra-filtration (6.54 vs 1.24 isoflavone:protein; p<0.001). Soy-protein and isoflavones are dissociated by water rinsing and prolonged cooking, but these have no equivalent in modern processes. As regards human health, a precise definition of the safety level of isoflavone intake requires additional studies.
Highlights
Soy has constituted a significant part of the Western human and animal diet since its industrialised processing started in the 1940s (Barnes, 2010, with references)
If isoflavones passed into the water at the second cooking stage, they remained in the soy-juice and Okara
The results indicated, that the longer the pre-cooking step, the lower the isoflavone content in the resulting soy-juice
Summary
Soy has constituted a significant part of the Western human and animal diet since its industrialised processing started in the 1940s (Barnes, 2010, with references). Soy isoflavones have undoubtedly become the most prevalent and potent xenoestrogens in human food (Omoruyi, Kabiersch, & Pohjanvirta, 2013). Xenoestrogens are known to impair reproduction efficiency It has been argued since the late 1950s, that reproductive endocrine disruption could reduce human fertility, resulting in fewer births in industrialised countries (Lang & Nuevo-Chiquero, 2012). Several scientists are hypothesising an adverse effect of environmental endocrine disruption that triggers reduced sperm count (Splingart et al, 2012), or increased incidence of spontaneous early miscarriages (Lang & Nuevo-Chiquero, 2012). At least partly, responsible for this situation, isoflavones, as the most prevalent xenoestrogens since the late 1950s in the human diet, should be considered as additional potential endocrine disruptors
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