Development and Validation of an HPLC–DAD Method for Analysis of the Six Major Isoflavones in Extracts from Soybean Processing

Changes in Isoflavone Profile from Soybean Seeds during Cheonggukjang Fermentation Based on High-Resolution UPLC-DAD-QToF/MS: New Succinylated and Phosphorylated Conjugates

In this study, thirty-eight isoflavone derivatives were comprehensively identified and quantified from the raw, steamed and fermented seeds of four selected soybean cultivars based on UPLC-DAD-QToF/MS results with reference to the previously reported LC-MS library and flavonoid database, and summarized by acylated group including glucosides (Glu), malonyl-glucosides (Mal-Glu), acetyl-glucosides (Ac-Glu), succinyl-glucosides (Suc-Glu) and phosphorylated conjugates (Phos) in addition to aglycones. Among them, Suc-Glu and Phos derivatives were newly generated due to fermentation by B. subtilis AFY-2 (cheonggukjang). In particular, Phos were characterized for the first time in fermented soy products using Bacillus species. From a proposed roadmap on isoflavone-based biotransformation, predominant Mal-Glu (77.5-84.2%, raw) decreased rapidly by decarboxylation and deesterification into Ac-Glu and Glu (3.5-8.1% and 50.0-72.2%) during steaming, respectively. As fermentation continued, the increased Glu were mainly succinylated and phosphorylated as well as gradually hydrolyzed into their corresponding aglycones. Thus, Suc-Glu and Phos (17.3-22.4% and 1.5-5.4%, 36 h) determined depending on cultivar type and incubation time, and can be considered as important biomarkers generated during cheonggukjang fermentation. Additionally, the changes of isoflavone profile can be used as a fundamental report in applied microbial science as well as bioavailability research from fermented soy foods.

Isolation of naturally occurring novel isoflavonoids: an update

This review covers the literature concerning the isolation and identification of new naturally occurring isoflavonoids from Leguminosae and non-Leguminous species between 2012–2017.

The isoflavone content of two new alfalfa-derived products for instant beverage preparation

The frequent use of plant-based products to promote health leads to the search for scientific information related to efficacy and safety of those products for human consumption. Two alfalfa-derived products (ADP), freeze-dried juice (FDJ) and dehydrated powder (DP), from alfalfa harvested in Mexico, are being developed as new possible nutraceuticals. To the best of our knowledge, any study reports the real composition of such products used to prepare instant beverages in what concerns isoflavone contents. Seven isoflavones (glycitein, formononetin, biochanin A, daidzein, genistein, daidzin and genistin) were assessed by HPLC-DAD analysis as well as its variation in five different batches of these products. Different solvents were tested in order to choose the best one to extract isoflavones. The results showed the presence of daidzein, genistein, genistin and daidzin in most samples while glycitein, formononetin and biochanin A were not detected. Significant differences between isoflavone contents were found with different solvent systems. Water was the best option to extract daidzein (0.40-1.08 mg per unit and 1.30-4.90 mg per unit for DP and FDJ, respectively) whereas the water-methanol-formic acid mixture was efficient to extract genistein (0.19-0.43 mg per unit and 0.15-0.72 mg per unit for DP and FDJ, respectively). In all cases, the total isoflavone content was higher in freeze-dried juices than in dehydrated powders. Genistein and daidzein were the more abundant isoflavones quantified. Further physiological and nutritional studies are needed to complete the validation of effectiveness and safety of these products.

Determination of free and bound phenolic compounds in soy isoflavone concentrate using a PFP fused core column

In the last years, the consumption of soy-based foods has increased due to the health benefits related to soy bioactives like phenolic compounds. Thus, in the present study, a new chromatographic method using reverse-phase high performance liquid chromatography coupled to diode array detection (RP-HPLC/DAD) was developed using a fused core pentafluorophenyl (PFP) column. The established method allowed the determination of twenty-one free phenolic compounds and eleven bound phenolics in a soy isoflavone concentrate. The method was validated in terms of precision and recovery. Intra and inter-day precision were less than 5% (% RSD) and the recovery was between 97.4% and 103.6%. Limits of quantification (LOQs) ranged between 0.093 and 0.443 μg/mL. Because of that, PFP stationary phase can be easily applied for routine determination of phenolic compounds in soy based foods.

High resolution LC-ESI-TOF-mass spectrometry method for fast separation, identification, and quantification of 12 isoflavones in soybeans and soybean products

A high resolution LC-ESI-TOF-MS analytical method was established for the rapid isolation, identification, and quantification of 12 isoflavones in soybean and soybean products. Individual isoflavones were identified on the basis of the accurate mass data of their respective protonated mass ions, Na or K adduct ions, fragment ions, and isotope ion patterns. The protonated mass ions of isoflavones were extracted for their quantification in soybean products. Twelve different isoflavones in the soybean products were fully separated, identified and quantified within 12min separation time. The established LC-TOF/MS was an effective analytical method for the simultaneous characterization and quantification of isoflavones with exceptionally short analytical time, high selectivity, a high linearity (r(2)>0.992) in a wide range, low LOD and LOQ, high precision, inter-and intra-day repeatability, and no significant matrix effect. Furthermore, it requires simple sample preparation procedure (solvent extraction, dilution, and syringe filtration).

Identification and quantification of the main isoflavones and other phytochemicals in soy based nutraceutical products by liquid chromatography-orbitrap high resolution mass spectrometry

The specific phytochemicals composition of soy nutritional supplements is usually not labelled. Hence, 12 dietary supplements were analyzed in order to detect and identify the main phytochemicals present in these samples, using a database containing 60 compounds. Ultra-high performance liquid chromatography coupled to single-stage Orbitrap high resolution mass spectrometry (UHPLC-Orbitrap-MS) has been used. Two consecutive extractions, using as extraction solvent a mixture of methanol:water (80:20, v/v), were employed, followed by two dilutions (10 or 100 times depending on the concentration of the components in the sample) with a mixture of an aqueous solution of ammonium acetate 30mM:methanol (50:50, v/v). The method was validated, obtaining adequate recovery and precision values. Limits of detection (LODs) and quantification (LOQs) were calculated, ranging from 2 to 150μgL(-1). Isoflavones were the predominant components present in the analyzed supplements with values higher than 93% of the total amount of phytochemicals in all cases. The aglycones (genistein, daidzein, glycitein and biochanin A) as well as their three conjugated forms, β-glucosides (genistin, daizin and glycitin) were detected and quantified, being daidzein the isoflavone detected at higher concentration in 8 out of 12 samples reported, with values ranging from 684 to 35,970mgkg(-1), whereas biochanin A was detected at very low concentrations, ranging from 18 to 50mgkg(-1). Moreover, other phytochemicals as flavones, flavonols, flavanones and phenolic acids were also detected and quantified.