Development of an Assay for Soy Isoflavones in Women’s Hair

Abstract

Soy isoflavones, at adequate dosages, have estrogenic and anti-thyroidal effects in animals and humans, which can either be beneficial or adverse, depending on the consumer’s physiological status. Hence, this study presents an assay of soy isoflavones in hair, aiming to give new information about a person’s exposure to isoflavones, when health issues related to estrogenic or thyroidal effects are observed. Aqueous or organic extraction procedures following acidic, basic, or enzymatic digestions were tested on 60 hair samples (from volunteers) from a hairdresser, and a clinical trial 2017T2-29. The acidic digestion method was the most efficient regarding isoflavones. A specific inquiry was developed to assess the dietary habits of French consumers based on the analysis of 12,707 food labels from France. It was used to check for the reliability of the new assay method. A score for the consumer exposures to isoflavones was built considering, among other parameters, soy-based diets and foodstuff containing soy as an ingredient, i.e., “hidden-soy”. The correlation between this score and isoflavone measurements in hair reached 0.947; p < 0.001. Therefore, providing that relevant data are considered to assess isoflavone exposure, hair that smoothens daily isoflavone intake variations, is a relevant tissue to assess human isoflavone exposure for subsequent health analyses.

Validation of ELISAs for Isoflavones and Enterolactone for Phytoestrogen Intake Assessment in the French Population

“…Indeed, based on measurements in the urine samples, 56.52% of the volunteers had detectable EQ concentrations, while based on plasma samples, 49.12% were defined as EQ-producers. These proportions were lower than those established in [ 30 ] on the same population and based on EQ measurements in hair (61.82%). This discrepancy was most probably explained because hair keeps a trace of previous exposures and metabolic transformations.…”

Traditional and Domestic Cooking Dramatically Reduce Estrogenic Isoflavones in Soy Foods

“…Despite recommendations from the French Food Safety Agency in 2005 [19], declaration of isoflavones content in soy-based foodstuffs is still not mandatory in France. However, considering the functional value of these substances, ELISAs were developed by our team in the late 1990s and have since been used to analyze these polyphenols in foods, biological fluids [20], and recently in hair [21]. This technique was validated in an international ring test monitored by TNO (Nederlandse Organisatie voor Toegepast Natuurwetenschappelijk Onderzoek, The Netherland) and results can be found in the work of Bennetau-Pelissero et al [20].…”

“…Nevertheless, data obtained using ELISA appeared reliable and comparable to the best chromatographic techniques challenged in this trial when aglycone forms were considered. Additionally, ELISAs have been validated in two studies designed to test food-frequency questionnaires assessing recent [22] and usual soy intakes [21]. To date, there is no legal technique for isoflavones determination in France.…”

Nondestructive Quantification of Isoflavones in Cotyledons by Near-Infrared Spectroscopy and Potential and Limits for Sustainable Soybean Breeding

“…Isoflavones are commonly quantified after separation by HPLC, followed by mass spectrometry or UV detection. Capillary electrophoresis and/or testing by enzyme-linked immunosorbent assay may also be applied [25][26][27][28]. These methods are widely used to quantify each isoflavone separately in various media such as seeds, tofu, milk, or flour.…”