Beta-glycosidase activity toward different glycosidic forms of isoflavones

New insights into the off-flavor improvement of soymilk by three grinding processing: Dry-blanching grinding, wet-blanching grinding, and wet-anaerobic grinding

Advances in grinding strategies have been beneficial to eliminating the off-flavor of soymilk and improving the quality soy products. Herein, four grinding processing, dry-blanching grinding (D-BG), wet-blanching grinding (W-BG), wet-anaerobic grinding (W-AG) and traditional grinding (TG) were employed and found to impose a significant impact on off-flavor components, accompanied by changes of hydroperoxides and free radicals. The results showed that all three methods could significantly hinder the formation of C6 aldehydes. C8 Alcohols and (E)-2-heptenal could be removed by D-BG, but lipids in dehulled soybean were prefer to be oxidized during storage, resulting in the accumulation of hydroperoxides and radicals. W-BG and W-AG have higher levels of 1-octen-3-ol, and soaking at an alkaline pH and increasing the number of rinses is beneficial for its removal. Gas chromatography-olfaction-mass spectrometry (GC-O-MS) combined with sensory evaluation showed that off-flavor profile of d-BGS, W-BGS and W-AGS was different. D-BG and W-AG possessed better flavor quality.

Advances in Extraction, Purification, and Analysis Techniques of the Main Components of Kudzu Root: A Comprehensive Review

Kudzu root (Pueraria lobate (Willd.) Ohwi, KR) is an edible plant with rich nutritional and medicinal values. Over the past few decades, an ample variety of biological effects of Pueraria isoflavone have been evaluated. Evidence has shown that Pueraria isoflavone can play an active role in antioxidant, anti-inflammatory, anti-cancer, neuroprotection, and cardiovascular protection. Over 50 isoflavones in kudzu root have been identified, including puerarin, daidzein, daidzin, 3'-hydroxy puerarin, and genistein, each with unambiguous structures. However, the application of these isoflavones in the development of functional food and health food still depends on the extraction, purification and identification technology of Pueraria isoflavone. In recent years, many green and novel extraction, purification, and identification techniques have been developed for the preparation of Pueraria isoflavone. This review provides an updated overview of these techniques, specifically for isoflavones in KR since 2018, and also discusses and compares the advantages and disadvantages of these techniques in depth. The intention is to provide a research basis for the green and efficient extraction, purification, and identification of Pueraria isoflavone and offers investigators a valuable reference for future studies on the KR.

The neuromodulatory effects of flavonoids and gut Microbiota through the gut-brain axis

Recent investigations show that dietary consumption of flavonoids could potentially confer neuroprotective effects through a variety of direct and indirect mechanisms. Numerous flavonoids have been shown to cross the BBB and accumulate within the central nervous system (CNS). Some of these compounds purportedly counteract the accumulation and deleterious effects of reactive oxygen species, fostering neuronal survival and proliferation by inhibiting neuroinflammatory and oxidative stress responses. Moreover, several studies suggest that gut microbiota may participate in regulating brain function and host behavior through the production and modulation of bioactive metabolites. Flavonoids may shape gut microbiota composition by acting as carbon substrates to promote the growth of beneficial bacteria that produce these neuroprotective metabolites, consequently antagonizing or suppressing potential pathogens. By influencing the microbiota-gut-brain axis through this selection process, flavonoids may indirectly improve brain health. This review examines the current state of research into the relationship between bioactive flavonoids, gut microbiota, and the gut-brain axis.

Use of kefir-derived lactic acid bacteria for the preparation of a fermented soy drink with increased estrogenic activity

Fermented foods are receiving growing attention for their health promoting properties. In particular, there is a growing demand for plant-based fermented foods as dairy alternatives. Considering that soy is a vegetal food rich in nutrients and a source of the phytoestrogen isoflavones, the aim of this study was to select safe food microorganisms with the ability to ferment a soy drink resulting in a final product with an increased estrogenic activity and improved functional properties. We used milk kefir grains, a dairy source of microorganisms with proven health-promoting properties, as a starting inoculum for a soymilk. After 14 passages of daily inoculum in fresh soy drink, we isolated four lactic acid bacterial strains: Lactotoccus lactis subsp. lactis K03, Leuconostc pseudomesenteroides K05, Leuconostc mesenteroides K09 and Lentilactobacillus kefiri K10. Isolated strains were proven to be safe for human consumption according to the assessment of their antibiotic resistance profile and comparative genomics. Furthermore, functional characterization of the bacterial strains demonstrated their ability to ferment sugars naturally present in soybeans and produce a creamy texture. In addition, we demonstrated, by means of a yeast-based bioluminescence reporter system, that the two strains belonging to the genus Leuconostoc increased the estrogenic activity of the soybean drink. In conclusion, the proposed application of the bacterial strains characterized in this study meets the growing demand of consumers for health-promoting vegetal food alternatives to dairy products.

Engineering of Leuconostoc citreum for Efficient Bioconversion of Soy Isoflavone Glycosides to Their Aglycone Forms

Soy isoflavones are phytochemicals that possess various beneficial physiological properties such as anti-aging, anti-tumor, and antioxidant properties. Since soy isoflavones exist in glycoside forms, their bioavailability requires initial hydrolysis of the sugar moieties bound to them to be efficiently absorbed through the gut epithelium. Instead of conventional chemical hydrolysis using acids or organic solvents, alternative strategies for enhancing the bioavailability of soy isoflavones using biological methods are gaining attention. Here, we engineered Leuconostoc citreum isolated from Korean kimchi for efficient bioconversion of soy isoflavone glycosides into their aglycone forms to enhance their bioavailability. We first constructed an expression module based on the isoflavone hydrolase (IH)-encoding gene of Bifidobacterium lactis, which mediates conversion of isoflavone glycosides to aglycone forms. Using a high copy number plasmid and bicistronic expression design, the IH was successfully synthesized in L. citreum. Additionally, we determined enzymatic activity of the IH using an in vivo β-glucosidase assay and confirmed its highly efficient bioconversion efficiency for various types of isoflavone glycosides. Finally, we successfully demonstrated that the engineered L. citreum could convert isoflavone glycosides present in fermented soymilk into aglycones.

Effect of pulsed electric field on soybean isoflavone glycosides hydrolysis by β-glucosidase: Investigation on enzyme characteristics and assisted reaction

This work aimed to investigate how pulsed electric field (PEF) technology as an alternative to enhance the enzymatic hydrolysis of soybean isoflavone glycosides (SIG). To achieve it, the effect of PEF treatment on the activity, kinetics, thermodynamics and structure of β-glucosidase (β-GLU) were evaluated. The parameters for PEF-assisted hydrolysis of soybean isoflavone glycosides were optimized by response surface methodology. The results showed that PEF treatment increased the relative activity and catalytic efficiency of β-GLU with moderate electric field intensity. Furthermore, PEF treatment induced the secondary and tertiary structural change of β-GLU, the α-helix content increased by 4.23% and the β-fold content decreased by 3.70%. The optimum conditions for PEF treatment were established as the highest yield of isoflavone aglycones achieved 94.58%. Therefore, these results indicated that PEF treatment could be used as an efficient process to improve the β-GLU properties, converting soybean isoflavone glycoside to their aglycones form.

Current perspectives on the beneficial effects of soybean isoflavones and their metabolites on plants

Soybeans have traditionally been a staple part of the human diet being highly rich in protein and lipid content. In an addition to the high nutritional components, soybeans have several functional components, like isoflavones, saponins, lecithin, and oligosaccharides. Soybeans emerge as a healthy functional food option. Isoflavones are most notable functional component of soybeans, exhibiting antioxidant activity while preventing plant-related diseases (e.g., antimicrobial and antiherbivore activities) and having positive effects on the life quality of plants. Isoflavones are thus sometimes referred to as phytochemicals. The latest research trends evince substantial interest in the biological efficacy of isoflavones in the human body as well as in plants and their related mechanisms. However, there is little information on the relationship between isoflavones and plants than beneficial human effects. This review discusses what is known about the physiological communication (transport and secretion) between isoflavones and plants, especially in soybeans.

Characterization of a novel isoflavone glycoside-hydrolyzing β-glucosidase from mangrove soil metagenomic library

For the beneficial pharmacological properties of isoflavonoids and their related glycoconjugates, there is increasingly interest in their enzymatic conversion. In this study, a novel β-glucosidase gene isolated from metagenomic library of mangrove sediment was cloned and overexpressed in Escherichia coli BL21(DE3). The purified recombination β-glucosidase, designated as r-Bgl66, showed high catalytic activity for soy isoflavone glycosides. It converted soy isoflavone flour extract with the productivities of 0.87 mM/h for daidzein, 0.59 mM/h for genistein and 0.42 mM/h for glycitein. The kcat/Km values for daidzin, genistin and glycitin were 208.73, 222.37 and 288.07 mM-1 s-1, respectively. In addition, r-Bgl66 also exhibited the characteristic of glucose-tolerance, and the inhibition constant Ki was 471.4 mM. These properties make it a good candidate in the enzymatic hydrolysis of soy isoflavone glycosides. This study also highlights the utility of metagenomic approach in discovering novel β-glucosidase for soy isoflavone glycosides hydrolysis.

Impact of processing technologies on isoflavones, phenolic acids, and antioxidant capacities of soymilk prepared from 15 soybean varieties

In the present study, soymilk samples were prepared from 15 soybean varieties by employing dry method-raw slurry filtration (D-BAF), dry method-cooked slurry filtration (D-BBF), wet method-raw slurry filtration (W-BAF), and wet method-cooked slurry filtration (W-BBF). Different varieties of soybean and processing techniques were found to impose a significant impact on total phenolics, total flavonoids, phenolic acids, isoflavones and antioxidant capacity of soymilk samples. Overall, the soymilk prepared by W-BAF exhibited a higher level of total phenolic content and antioxidant activity. The soymilk samples prepared by W-BBF presented higher values for total flavonoid content and ferric-reducing antioxidant power assay. The soymilk prepared by W-BBF presented higher subtotal values of phenolic acids. In comparison, the soymilk prepared by D-BAF exhibited high amount of total isoflavones followed by the soymilk processed by W-BAF. Overall, the wet method was found to be responsible for improved phenolic contents and antioxidant activity of soymilk sample.

Characterization of a GH3 halophilic β-glucosidase from Pseudoalteromonas and its NaCl-induced activity toward isoflavones

A novel β-glucosidase gene was isolated from Pseudoalteromonas sp. GXQ-1 and heterologously expressed in Escherichia coli. The activity of the encoded enzyme, PABGL, toward p-nitrophenyl-β-D-glucopyranoside was increased 8.74-fold by the presence of 3 M NaCl relative to the absence of added NaCl. PABGL hydrolyzed a variety of soy isoflavone substrates. For the conversion of daidzin to daidzein, the production rate was 1.44 mM/h. The addition of NaCl enhanced the hydrolytic activity of PABGL toward daidzin and genistein; the maximum activation by NaCl was 3.48- and 6.79-fold, respectively. This is the first report of a halophilic β-glucosidase from Pseudoalteromonas spp., and represents the β-glucosidase with the highest multiple of activation by NaCl. PABGL exhibits strong potential for applications in food processing and industrial production.

Bioconversion and bioaccessibility of isoflavones from sogurt during in vitro digestion

This study investigated the bioconversion and bioaccessibility of soy isoflavones produced in sogurt fermented with S. thermophilus and L. bulgaricus during in vitro digestion. The highest survivability of S. thermophilus (6.49 log cfu/mL) and L. bulgaricus (6.48 log cfu/mL) was in oral phase. In gastric phase, the total aglycones of sogurt (26.73 g/L) increased up to 20 times than control (1.21 g/L), with a significant increase in daidzein (17.05 g/L) and genistein (9.68 g/L). Addition of 8U of β-glucosidase into soymilk significantly increased the conversion of isoflavone in ENTII (daidzein: 0.46 g/L; genistein: 0.18 g/L) than in ENTI (daidzein: 0.33 g/L; genistein: 0.20 g/L). The particle size analysis and confocal micrographs of digesta also suggest the size of fat and protein in gastric phase to be smaller than in intestinal phase. The results indicate the prospective to develop soy-based fermented products capable of releasing high isoflavone in the digestive system.

Metabolic Engineering of Microorganisms for the Production of Flavonoids

Flavonoids are a class of secondary metabolites found in plant and fungus. They have been widely used in food, pharmaceutical, and nutraceutical industries owing to their significant biological activities, such as antiaging, antioxidant, anti-inflammatory, and anticancer. However, the traditional approaches for the production of flavonoids including chemical synthesis and plant extraction involved hazardous materials and complicated processes and also suffered from low product titer and yield. Microbial synthesis of flavonoids from renewable biomass such as glucose and xylose has been considered as a sustainable and environmentally friendly method for large-scale production of flavonoids. Recently, construction of microbial cell factories for efficient biosynthesis of flavonoids has gained much attention. In this article, we summarize the recent advances in microbial synthesis of flavonoids including flavanones, flavones, isoflavones, flavonols, flavanols, and anthocyanins. We put emphasis on developing pathway construction and optimization strategies to biosynthesize flavonoids and to improve their titer and yield. Then, we discuss the current challenges and future perspectives on successful strain development for large-scale production of flavonoids in an industrial level.

Deglycosylation patterns of isoflavones in soybean extracts inoculated with two enzymatically different strains of lactobacillus species

Microorganism selection is critical to deglycosylation in soybean fermentation for producing beneficial phytochemicals. This study investigated isoflavone bioconversion in soybean extract inoculated with Lactobacillus plantarum K2-12 and Lactobacillus curvatus JD0-31 exhibiting different enzyme activities. L. plantarum showed higher esterase (C4), esterase (C8), β-galactosidase, α-glucosidase, β-glucosidase, and N-acetyl-β-glucosaminase activities. We found that isoflavone bioconversion was distinguished into isoflavone backbone structure types. Malonyl- and acetyl- types of isoflavones except for malonyl daidzin were not significantly differed their contents between lactobacilli. Deglycosylating severity was observed in malonyl genistin in both lactobacilli, resulting mass production of genistein. On the other hand, daidzein glycosides were dependable to lactobacilli, in which L. plantarum efficiently degraded malonyl daidzin and daidzin in fast time. Glycitein was most degradable among the three aglycones by fermentation. These results suggest that efficient control of isoflavone deglycosylation by Lactobacillus species should be controlled to the inoculation period and select target isoflavones.

Soybean ultrasound pre-treatment prior to soaking affects β-glucosidase activity, isoflavone profile and soaking time

Ultrasound may convert conjugated isoflavones into their corresponding aglycones, the best form for absorption in the human body. However, ultrasound may also influence the activity of endogenous β-glucosidase. Therefore, the present work evaluated the effects of soybean ultrasound pre-treatment by applying the Box-Behnken design prior to soaking, a step that is important for industries to prepare certain soy products. Furthermore, a multi-response optimisation is provided. The best conditions for soybean ultrasound pre-treatment were established as temperature, X1 = 55 °C; exposure time, X2 = 5 min and ultrasound intensity, X3 = 19.5 W cm-2. Under these conditions, soybeans with higher contents of aglycones were obtained and β-glucosidase activity was kept as high as possible. A second experiment was conducted and confirmed that ultrasound pre-treatment results in a lower soaking time (2 h) to achieve the highest moisture content, lower hardness as well as increased content of aglycones.

Metabolism of the Strobilurin Fungicide Mandestrobin in Wheat

The metabolic fate of a new fungicide, mandestrobin, labeled with ¹⁴C at the phenoxy or benzyl ring was examined in wheat after a single spray application at 300 g/ha. Mandestrobin penetrated into foliage over time, with both radiolabels showing similar ¹⁴C distribution in wheat, and 2.8-3.3% of the total radioactive residue remained on the surface of straw at the final harvest. In foliage, mandestrobin primarily underwent mono-oxidation at the phenoxy ring to produce 4-hydroxy or 2-/5-hydroxymethyl derivatives, followed by their subsequent formation of malonylglucose conjugates. In grain, the cleavage of its benzyl phenyl ether bond was the major metabolic reaction, releasing the corresponding alcohol derivative, while the counterpart 2,5-dimethylphenol was not detected. The constant RS enantiomeric ratio of mandestrobin showed its enantioselective metabolism to be unlikely on/in wheat.

Characterization of two extracellular β-glucosidases produced from the cellulolytic fungus Aspergillus sp. YDJ216 and their potential applications for the hydrolysis of flavone glycosides

A cellulolytic fungus YDJ216 was isolated from a compost and identified as an Aspergillus sp. strain. Two extracellular β-glucosidases, BGL1 and BGL2, were purified using ultrafiltration, ammonium sulfate fractionation, and High-Q chromatography. Molecular masses of BGL1 and BGL2 were estimated to be 97 and 45 kDa, respectively, by SDS-PAGE. The two enzymes eluted as one peak at 87 kDa by Sephacryl S-200 chromatography, and located at similar positions in a zymogram after intact gel electrophoresis, suggesting BGL1 and BGL2 might be monomeric and dimeric, respectively. Both enzymes showed similar enzymatic properties; they were optimally active at pH 4.0-4.5 and 60 °C, and had similar half-lives at 70 °C. Two enzymes also preferred p-nitrophenyl glucose (pNPG) with the same K_m and hardly hydrolyzed cellobiose, suggesting both enzymes are aryl β-glucosidases. However, V_max for pNPG of BGL1 (953.2 U/mg) was much higher than those of BGL2 (66.5U/mg) and other β-glucosidases reported. When tilianin (a flavone glycoside of acacetin) was reacted with both enzymes, inhibitory activity for monoamine oxidase, relating to oxidation of neurotransmitter amines, was increased closely to the degree obtained by acacetin. These results suggest that BGL1 and BGL2 could be used to hydrolyze flavone glycosides to improve their inhibitory activities.

Effect of dietary supplementation with Lactobacillus acidophilus D2/CSL (CECT 4529) on caecum microbioma and productive performance in broiler chickens

This study examines the effects of the dietary supplementation with Lactobacillus acidophilus D2/CSL (CECT 4529) (LA) on productive performances, incidence of foot pad dermatitis and caecum microbioma in broiler chickens. A total of 1,100 one-day old male Ross 308 chicks were divided into 2 groups of 16 replicates with 25 birds each and reared from 1–41 d. One group was fed a basal diet (CON) and the other group the same diet supplemented with LA. Caecum contents were collected from 4 selected birds at day one and 5 selected birds at the end of the rearing period. Then, they were submitted to DNA extraction and whole DNA shotgun metagenomic sequencing. Overall, the LA supplementation produced a significant beneficial effect on body weight gain between 15–28 d and improved feed conversion rate in the overall period. On the contrary, litter moisture, pH and incidence of the foot pad lesions were not affected by LA. Birds treated with LA showed a lower occurrence of pasty vent at both 14 and 28 d. At the end of the rearing period, Lachanospiraceae were significantly higher in LA birds in comparison to CON (17.07 vs 14.39%; P = 0.036). Moreover, Ruminococcus obeum, Clostridium clostridioforme, Roseburia intestinalis, Lachnospiraceae bacterium 14-2T and Coprococcus eutactus were significantly higher in LA birds in comparison to CON. The relative abundance of Lactobacillus acidophilus was comparable between LA and CON groups. However, a positive effect was observed in relation to the metabolic functions in the treated group, with particular reference to the higher abundance of β-glucosidase. In conclusion, the LA supplementation improved broiler productive performances and metabolic functions promoting animal health.

Kinetic study of application of graphene oxide as a catalyst to accelerate extraction of total flavonoids from Radix Scutellaria

A new kinetic model, So's three-step kinetic model, was used to study the kinetics of graphene oxide (GO)-assisted ethanol reflux extraction (GERE).

Effect of Cooking on Isoflavones, Phenolic Acids, and Antioxidant Activity in Sprouts of Prosoy Soybean (Glycine max)

Soy sprouts possess health benefits and is required to be cooked before consumption. The effects of cooking on the phenolic components and antioxidant properties of soy sprouts with different germination days were investigated. A food-grade cultivar Prosoy with a high protein content was germinated for 1, 2, 3, 5, and 7 d and cooked till palatable for 20, 20, 5, 5, and 7 min, respectively. Total phenolic content (TPC), total flavonoids content (TFC), condensed tannins content (CTC), individual phenolic acids, isoflavones, DPPH, ferric-reducing antioxidant power (FRAP), and oxygen radical absorbance capacity (ORAC) of raw and cooked sprouts were measured. Cooking caused significant losses in phenolic content and antioxidant activities, and maximum loss was on day 3 > 5 > 7, including TPC (32%, 23%, and 15%), TFC (50%, 44%, and 20%), CTC (73%, 47%, and 12%), DPPH (31%, 15%, and 5%), FRAP (34%, 25%, and 1%), and ORAC (34%, 22%, 32%), respectively. Cooking caused significant losses in most individual phenolic acid, benzoic group, cinnamic group, total phenolic composition, individual isoflavones, and total isoflavones. The losses of phenolic acids such as gallic, protocatechuic, hydroxybenzoic, syringic, chlorogenic, or sinapic acids during cooking were not compensated by the increases in trihydroxybenzoic, vanillic or coumaric acids on certain days of germination. Cooking caused minimal changes in phenolic acid composition of day 1 and 2 sprouts compared to 3, 5, and 7 d sprouts.

Effect of Monascus aged vinegar on isoflavone conversion in soy germ by soaking treatment

Soy germ rich in isoflavones has attracted much attention for health-promoting characteristics. An effective approach via Monascus aged vinegar soaking was adopted to enhance the aglycone amount. The profiles and interconversion of soy germ isoflavones via Monascus aged vinegar soaking were investigated, and the distribution in vinegars were also explored. The aglycones were dramatically increased by 40.76 times. Concomitantly, β-glycosides and malonylglycosides were significantly decreased. The proportion of aglycones presented a sharp increase with the endogenous β-glucosidase activity at the initial 4h incubation. There appeared to be correlations between β-glucosidase activity and the hydrolysis of conjugated isoflavones. The results demonstrated that the reactions of decarboxylation, de-esterification and de-glycosylation were involved in the Monascus aged vinegar soaking, supporting synergistic effects of enzymolysis by endogenous β-glucosidase from soy germ and acid hydrolysis of vinegars. Soaking by vinegar is a promising pathway for preparing aglycone-rich soy germ.

Changes in soymilk during fermentation with kefir culture: oligosaccharides hydrolysis and isoflavone aglycone production

The objective of this study was to evaluate the changes in oligosaccharides and isoflavone aglycone content in soymilk during fermentation with commercial kefir culture. Soymilk was fermented with kefir culture at 25 °C for 30 h. The counts of lactic acid bacteria, Lactococcus lactis, Leuconostoc sp and yeasts; measurements of pH, acidity, α-galactosidase and β-glucosidase activity, sugar and isoflavone contents were performed at the intervals of time. In the fermented soymilk, the lactic acid bacteria counts increased from 7.6 log to 9.1 CFU g(-1), pH reached to 4.9 and lactic acid reached 0.34 g 100  g(- 1). The α-galactosidase was produced (0.016 AU g(-1)) with 100% raffinose and 92% stachyose hydrolysis being observed after the depletion of galactose, glucose and sucrose. Kefir culture produced β-glucosidase (0.0164 AU g(-1)), resulting in 100% bioconversion of glycitin and daidzin and 89% bioconversion of genistin into the corresponding aglycones. The fermented soymilk presented 1.67 μmol g(-1) of daidzein, 0.28 μmol g(-1) of glicitein and 1.67 μmol g (-1) of genistein.

Malonylglucoside conjugates of isoflavones are much less bioavailable compared with unconjugated β-glucosidic forms in rats

Despite considerable interest in the physiologic effects of isoflavones, the in vivo bioavailability of the most common isoflavone forms, malonylglucoside conjugates, has not been determined. Differences in the bioavailability of malonylglucosides compared with the nonconjugated β-glucoside forms may explain the inconsistent findings regarding the physiologic effects of isoflavones. Therefore, our objective was to determine the effect of malonyl- conjugation on isoflavone bioavailability in an animal model. Malonylgenistin and malonyldaidzin, and their corresponding nonconjugated glucosides, were extracted from soy grits and purified using liquid chromatography. Purity of the isolated forms was confirmed by nuclear magnetic resonance analysis. Male rats were gavaged with malonylgenistin, genistin, malonyldaidzin, or daidzin at a dose of 100 μmol/kg body weight. Blood and urine samples were collected at time intervals ranging from 0 to 48 h. Isoflavone metabolites in plasma and urine were determined using stable isotope dilution-liquid chromatography/mass spectrometry. Comparisons of pharmacokinetic variables were made between nonconjugated and conjugated glucosides and over time of plasma collection. The areas under the time-concentration curve of the metabolites in the plasma obtained after the administration of nonconjugated β-glucosides were 1 to 6 times higher than those of their respective malonylglucosides (P ≤ 0.05). Additionally, maximum plasma concentration and urinary excretion of isoflavone metabolites were significantly higher (1-9 times; P ≤ 0.05) after the administration of nonconjugated β-glucosides. To our knowledge, these results demonstrated, for the first time, that nonconjugated β-glucosides are relatively more bioavailable than their respective malonylglucosides. These differences in the bioavailability of conjugated and nonconjugated β-glucosides should be considered in future studies focused on the bioactivity of isoflavones.

Malonyl isoflavone glucosides are chiefly hydrolyzed and absorbed in the colon

Malonyl isoflavone glucosides are water-soluble derivatives of soybean hypocotyls. This study compared the hydrolysis and absorption of malonyl isoflavone glucosides and nonmalonyl isoflavone glucosides in rats. Plasma concentrations of isoflavones were measured after oral administration of malonyl isoflavone glucosides or isoflavone glucosides. After fasting, the duodenum, jejunum, ileum, and colon were excised, and homogenates were prepared. The extent of hydrolysis of each glucoside by each intestinal homogenate was measured. Plasma levels of isoflavone aglycones, such as daidzein and glycitein, were higher in rats administered malonyl isoflavone glucosides than in those administered isoflavone glucosides. The area under the curve of daidzein in plasma of rats administered malonyl isoflavone glucosides was also significantly greater than that in those administered isoflavone glucosides. A transport experiment using Caco-2 cells suggested that degradation of malonyl glucosides to aglycones is necessary for intestinal absorption. Malonyl isoflavone glucosides were hydrolyzed only in the colon, whereas hydrolysis of isoflavone glucosides occurred in the jejunum, ileum, and colon. These results indicated more effective absorption of malonyl isoflavone glucosides than of nonmalonyl isoflavone glucosides. Moreover, effective absorption of malonyl isoflavone aglycones in the colon contributed to the significant increase in plasma isoflavone levels.

Deglycosylation of isoflavones in isoflavone-rich soy germ flour by Aspergillus oryzae KACC 40247

Aspergillus oryzae KACC 40247 was selected as an efficient daidzein-producing fungus from strains of the genus Aspergillus by using 5% (w/v) soy germ flour (SGF) as an isoflavone-glycoside-rich medium. The culture conditions, including SGF concentration, agitation speed, initial pH, temperature, and time, were optimized as follows: 7% (w/v) SGF, initial pH 6.0, 33 °C, 300 rpm, and 24 h in a 100 mL baffled flask. The determined amount of isoflavone aglycons in SGF using 50% ethyl acetate was the highest among the solvent systems tested and it was 3.7-fold higher than that using 70% methanol. Under the optimized conditions, the content and concentration of daidzein were 134 mg/g of SGF and 9.4 g/L, respectively, with a productivity of 391 ± 2.8 mg/L/h, and those of isoflavone aglycons were 165 mg/g of SGF and 11.5 g/L, respectively, with a productivity of 479 mg/L/h. Optimization of culture conditions increased the content, concentration, and productivity of isoflavone aglycons by 3.1-, 3.0-, and 3.7-fold, respectively. To our knowledge, this is the highest production of isoflavone aglycons reported to date.

Optimisation of soy flour fermentation parameters to produce β-glucosidase for bioconversion into aglycones

The solid state fermentation (SSF) parameters of defatted soybean flour (DSF) with Aspergillus oryzae IOC 3999/1998 or Monascus purpureus NRRL 1992 was evaluated using a rotational central composite experimental design to optimise the production of β-glucosidase and convert glycosidic isoflavones in aglycones. Variables investigated were initial pH of DSF, volume of water added to 10 g of DSF and incubation temperature. β-Glucosidase activity was measured using the synthetic substrate, p-nitrophenyl-β-D-glucoside. The content of isoflavones was determinate by ultra performance liquid chromatography. The highest production of β-glucosidase for both strains occurred when adding 10 mL of water to the DSF, incubating at 30 °C and using 6.0 as the initial DSF pH. A. oryzae IOC 3999/1998 expressed β-glucosidase activity at 10.7 times higher than M. purpureus NRRL 1992. The DSF fermentation was more efficient in converting isoflavones with M. purpureus NRRL 1992.

A family 3 glycosyl hydrolase of Dickeya dadantii 3937 is involved in the cleavage of aromatic glucosides

Dickeya dadantii is a phytopathogenic bacterium secreting a large array of plant-cell-wall-degrading enzymes that participate in the infection and maceration of the host plant tissue. Sequencing of the D. dadantii 3937 genome predicted several genes encoding potential glycosidases. One of these genes, bgxA, encodes a protein classified in family 3 of glycosyl hydrolases. Inactivation of bgxA and the use of a gene fusion revealed that this gene is not essential for D. dadantii pathogenicity but that it is expressed during plant infection. The bgxA expression is induced in the presence of glycosidic or non-glycosidic aromatic compounds, notably ferulic acid, cinnamic acid, vanillic acid and salicin. The BgxA enzyme has a principal β-d-glucopyranosidase activity and a secondary β-d-xylopyranosidase activity (ratio 70 : 1). This enzyme activity is inhibited by different aromatic glycosides or phenolic compounds, in particular salicin, arbutin, ferulic acid and vanillic acid. Together, the induction effects and the enzyme inhibition suggest that BgxA is mostly involved in the cleavage of aromatic β-glucosides. There is evidence of functional redundancy in the D. dadantii β-glucoside assimilation pathway. In contrast to other β-glucoside assimilation systems, involving cytoplasmic phospho-β-glucosidases, the cleavage of aromatic glucosides in the periplasmic space by BgxA may avoid the release of a toxic phenolic aglycone into the cytoplasm while still allowing for catabolism of the glucose moiety.

Phytochemical composition of Potentilla anserina L. analyzed by an integrative GC-MS and LC-MS metabolomics platform

Potentilla anserina L. (Rosaceae) is known for its beneficial effects of prevention of pre-menstrual syndrome (PMS). For this reason P. anserina is processed into many food supplements and pharmaceutical preparations. Here we analyzed hydroalcoholic reference extracts and compared them with various extracts of different pharmacies using an integrative metabolomics platform comprising GC-MS and LC-MS analysis and software toolboxes for data alignment (MetMAX Beta 1.0) and multivariate statistical analysis (COVAIN 1.0). Multivariate statistics of the integrated GC-MS and LC-MS data showed strong differences between the different plant extract formulations. Different groups of compounds such as chlorogenic acid, kaempferol 3-O-rutinoside, acacetin 7-O-rutinoside, and genistein were reported for the first time in this species. The typical fragmentation pathway of the isoflavone genistein confirmed the identification of this active compound that was present with different abundances in all the extracts analyzed. As a result we have revealed that different extraction procedures from different vendors produce different chemical compositions, e.g. different genistein concentrations. Consequently, the treatment may have different effects. The integrative metabolomics platform provides the highest resolution of the phytochemical composition and a mean to define subtle differences in plant extract formulations.

Effects of food formulation and thermal processing on flavones in celery and chamomile

Flavones isolated from celery varied in their stability and susceptibility to deglycosylation during thermal processing at pH 3, 5, or 7. Apigenin 7-O-apiosylglucoside was converted to apigenin 7-O-glucoside when heated at pH 3 and 100°C. Apigenin 7-O-glucoside showed little conversion or degradation at any pH after 5h at 100°C. Apigenin, luteolin, and chrysoeriol were most stable at pH 3 but progressively degraded at pH 5 or 7. Chamomile and celery were used to test the effects of glycosidase-rich foods and thermal processing on the stability of flavone glycosides. Apigenin 7-O-glucoside in chamomile extract was readily converted to apigenin aglycone after combination with almond, flax seed, or chickpea flour. Apigenin 7-O-apiosylglucoside in celery leaves was resistant to conversion by β-glucosidase-rich ingredients, but was converted to apigenin 7-O-glucoside at pH 2.7 when processed at 100°C for 90min and could then be further deglycosylated when mixed with almond or flax seed. Thus, combinations of acid hydrolysis and glycosidase enzymes in almond and flax seed were most effective for developing a flavone-rich, high aglycone food ingredient from celery.

Design and selection of soy breads used for evaluating isoflavone bioavailability in clinical trials

To modulate isoflavone aglycone composition within a soy functional food, soy ingredients were processed and evaluated in a soy bread system intended for clinical trials. A soy flour/soy milk mixture (SM) was boiled, fermented, steamed, or roasted prior to dough preparation. The isoflavone compositions of five processed SM and their corresponding breads combined with and without β-glucosidase-rich almonds were examined using HPLC. Isoflavone malonyl-glucosides (>80%) were converted into acetyl and simple glucoside forms (substrates more favorable for β-glucosidase) in steamed and roasted SM. Their corresponding breads had isoflavones predominately as aglycones (∼75%) with soy-almond bread with steamed SM being more consumer acceptable than roasted. Isoflavone composition in soy bread was stable during frozen storage and toasting. A suitable glycoside-rich soy bread (31.6 ± 2.1 mg aglycone equiv/slice) using unprocessed SM and an aglycone-rich soy-almond bread (31.1 ± 1.9 mg aglycone equiv/slice) using steamed SM were developed to evaluate fundamental questions of isoflavone bioavailability in clinical trials.

Isoflavone retention during processing, bioaccessibility, and transport by Caco-2 cells: effects of source and amount of fat in a soy soft pretzel

The impact of source and amount of lipid used to prepare a soy soft pretzel on the bioaccessibility and transport of isoflavones was investigated using the coupled in vitro digestion/Caco-2 human cell model. Pretzels were prepared without or with 2.9 or 6.0% exogenous lipid from either shortening, canola oil, ground almond, or ground hazelnut. The isoflavone backbone structure was stable during pretzel production, although there was partial conversion from malonyl and acetyl glucosides to simple glucosides and aglycones. Endogenous β-glucosidase activity in ground almond facilitated partial conversion of simple glucosides to aglycones during proofing, resulting in a slight decrease in bioaccessibility of isoflavones as compared with other sources of lipid. Amount and source of lipid did not affect bioaccessibility or uptake and metabolism of isoflavones by Caco-2 cells, although transport across the monolayer was greater with the lesser amount of shortening. These results suggest that the isoflavone structure, but not source or amount of lipid in a soy pretzel, may affect bioavailability of isoflavones.

Evaluation of biological activities of a groundnut (Apios americana Medik) extract containing a novel isoflavone

Groundnut (Apios americana Medik) contains a novel isoflavone, genistein-7-O-gentiobioside. In the present study, we examined the biological activities of an alcohol extract of groundnut containing genistein-7-O-gentiobioside as the main component. Although the groundnut extract by itself did not show antioxidative activity, it drove the antioxidative system in cells. Pretreatment of human breast carcinoma MCF-7 cells for 24 h with the groundnut extract and soybean isoflavone increased gene expression of heme oxygenase-1 (HO-1), a major antioxidative stress enzyme. These groundnut extract-treated cells showed antioxidative activity against free radicals derived from a radical initiator. Pretreatment of cells with 100 μg/mL groundnut extract prevented the depletion of glutathione by the radical initiator; however, treatment with 100 μg/mL of soybean isoflavone injured the cell membrane, indicating that glutathione might be released to the extracellular environment. These results suggest that the groundnut extract had isoflavone-like activity. Like soybean, groundnuts are a good source of isoflavones.

Molecular cloning and characterization of a novel β-glucosidase with high hydrolyzing ability for soybean isoflavone glycosides and glucose-tolerance from soil metagenomic library

A novel β-glucosidase (Bgl1269) was identified from a metagenomic library of mangrove soil by activity-based functional screening. Sequence analysis revealed that Bgl1269 encodes a protein of 422 amino acids. After being overexpressed in Escherichia coli and purified, the enzymatic properties of Bgl1269 were investigated. The recombinant enzyme displayed a pH optimum of 6.0 and a temperature optimum of 40°C, and the addition of most common metal ions (1 or 10mM) increased the enzymatic activity evidently. In addition, the enzyme showed high hydrolyzing ability for soybean isoflavone glycosides, and 0.8unit of enzyme could completely converted daidzin and genistin (0.5mg/mL) to daidzein and genistein at 40°C for 0.5h. Interestingly, Bgl1269 also exhibited a very high glucose-tolerance, with the highest inhibition constant K(i) (4.28M) among β-glucosidases reported so far. These properties make it a good candidate in the production of soybean isoflavone aglycones after further study.

Separation of soybean isoflavone aglycone homologues by ionic liquid-based extraction

The separation of a compound of interest from its structurally similar homologues is an important and challenging problem in producing high-purity natural products, such as the separation of genistein from other soybean isoflavone aglycone (SIA) homologues. The present work provided a novel method for separating genistein from its structurally similar homologues by ionic liquid (IL)-based liquid-liquid extraction using hydrophobic IL-water or hydrophilic IL/water-ethyl acetate biphasic systems. Factors that influence the distribution equilibrium of SIAs, including the structure and concentration of IL, pH value of the aqueous phase, and temperature, were investigated. Adequate distribution coefficients and selectivities over 7.0 were achieved with hydrophilic IL/water-ethyl acetate biphasic system. Through a laboratory-scale simulation of fractional extraction process containing four extraction stages and four scrubbing stages, genistein was separated from the SIA homologues with a purity of 95.3% and a recovery >90%.