Tracking Isoflavones in Whole Soy Flour, Soy Muffins and Plasma after Consumption of Muffins by Healthy Adults

Abstract

The cardio‐protective effect of soy may be related to isoflavones. Research is needed to determine how isoflavones change during processing and digestion from a raw food ingredient to the biological fluid in order to better understand the relationship between isoflavone form, the food matrix, and the health effects conferred. This study tracked the abundance and transformation of soy isoflavones in: de‐fatted whole soy flour; a baked soy muffin; and plasma after regular consumption of soy muffins in a human clinical trial. Isoflavones were identified and quantified in soy flour and muffins by HPLC, and in plasma by LC‐MS/MS after participants (n=162) consumed soy muffins at doses of either 12.5g or 25g soy protein daily for 6 weeks. Soy muffins were sampled from 7 different production days (n=14) and analyzed for individual isoflavone isoforms and total isoflavone. Mean (±SEM) isoflavone content was 4.14±1.29 mg/g (DW) in soy flour and 1.10±0.04 mg/g (DW) in soy muffins. Soy flour and muffins contained similar proportions of isoflavone isoforms, but soy muffins contained overall lower absolute isoflavone content. Median total plasma isoflavone concentrations at week 6 for the low dose soy and the high dose soy groups were 91.0 and 333.7 ng/mL, respectively. Baking soy flour does not result in major changes in the relative proportion of isoflavones isoforms. Regular consumption of soy results in a dose‐related increase in plasma isoflavones with an approximate 4‐fold increase with a doubling of the dose. Funded through the Government of Canada Growing Forward I Science substantiation Program (RBPI#1746).