Recent advances in the microbial hydroxylation and reduction of soy isoflavones

Abstract

Soy isoflavones are naturally occurring phytochemicals, which are biotransformed into functional derivatives through oxidative and reductive metabolic pathways of diverse microorganisms. Such representative derivatives, ortho-dihydroxyisoflavones (ODIs) and equols, have attracted great attention for their versatile health benefits since they were found from soybean fermented foods and human intestinal fluids. Recently, scientists in food technology, nutrition and microbiology began to understand their correct biosynthetic pathways and nutraceutical values, and have attempted to produce the valuable bioactive compounds using microbial fermentation and whole-cell/enzyme-based biotransformation. Furthermore, artificial design of microbial catalysts and/or protein engineering of oxidoreductases were also conducted to enhance production efficiency and regioselectivity of products. This minireview summarizes and introduces the past year's studies and recent advances in notable production of ODIs and equols, and provides information on available microbial species and their catalytic performance with perspectives on industrial application.

Where to Look into the Puzzle of Polyphenols and Health? The Postbiotics and Gut Microbiota Associated with Human Metabotypes

“…From Uro‐M5, consecutive dehydroxylations finally lead to the main metabolites detected in vivo, which are the dihydroxy‐urolithins urolithin A (Uro‐A) and isourolithin A (IsoUro‐A) and 3‐hydroxy‐urolithin, also known as urolithin B (Uro‐B) ( Figure 1 ). [ 80–82 ]…”

“…For a detailed description of the pathways, see the studies by García‐Villalba et al. [ 81 ] for the catabolism of ellagic acid to urolithins; and Lee et al., [ 82 ] for the catabolism of isoflavones. The circles specifically enclose the final urolithins for each metabotype (red, UM‐B; blue, UM‐A).…”

Flavonoid Production: Current Trends in Plant Metabolic Engineering and De Novo Microbial Production

“…To date, hydroxylated flavonoid production remains a major challenge because P450-related enzymes of plants are not effectively expressed in microorganisms [ 130 ]. Moreover, the hydroxylation of flavonoids has been studied less, as compared to methylation and glycosylation processes [ 143 ]. Lv et al [ 130 ] used a modular approach for the construction, characterization, and optimization of flavonoid pathways in Yarrowia lipolytica for the synthesis of flavonoids and hydroxylated flavonoids.…”

“…After the removal of precursor pathway limitations and further optimization, their engineered strain produced 15.8-fold more naringenin (252.4 mg/L), 6.9-fold more eriodictyol (134.2 mg/L), and 8.8-fold more taxifolin (110.5 mg/L) from glucose in the flasks. Recent advancements in the hydroxylation of isoflavones by microbes have been reviewed elsewhere [ 143 ]. In recent years, more progress has been made toward increasing eriodictyol production and introducing metabolic pathways in various microbes.…”

The Oxidation of Equol by Tyrosinase Produces a Unique Di-ortho-Quinone: Possible Implications for Melanocyte Toxicity

“…Nevertheless, it has not yet been reported whether EQ 1 acts as a substrate for tyrosinase as does RD and RES. However, since tyrosinase has recently been adopted for efficient isoflavone hydroxylation in recombinant strains [28] and EQ 1 has a unique structure that has two phenolic groups, the oxidation of EQ 1 by tyrosinase is expected to give rise to EQ-quinone-A and -B as intermediates, which are then oxidized to EQ-quinone-C (Figure 1). These EQ-quinones can be identified after being reduced with NaBH 4 or L-ascorbic acid (AA) to their corresponding catechols, as was performed to identify the o-quinones of RD and RES [22,27].…”