Isoflavone Levels Research Articles

Analysis of isoflavone content in tempeh, a fermented soybean, and preparation of a new isoflavone-enriched tempeh

To produce a tempeh-like functional food containing a high level of isoflavone with a high absorptivity, we analyzed changes in the composition of isoflavone during tempeh fermentation and the difference in isoflavone content depending on the soybean variety and particular tissue. By adding soybean germ (hypocotyl) that contained a large amount of isoflavone, we prepared a new isoflavone-enriched tempeh in the form of a granular fermented soybean-based food, which can serve as a nutritious supplement for the elderly.

Identification of equol producers in a Japanese population by high-performance liquid chromatography with coulometric array for determining serum isoflavones

Using a method of high-performance liquid chromatography (HPLC) with coulometric array, we measured isoflavone levels in sera from seven volunteers before and after three days of ingesting Soyaflavone E (an isoflavones powder) and from 129 female farmers (Japanese Multiple Environmental Toxicants Study; JMETS). Results showed that the serum isoflavone concentrations rose dramatically after three days of ingesting Soyaflavone E in all subjects except for the serum equol concentrations in two subjects. The geometric mean concentrations of daidzein, genistein, and equol in the serum of 129 Japanese women were 25.0 ng/ml of daidzein, 94.1 ng/ml of genistein, and 9.6 ng/ml of equol. Interestingly, there existed two dominant groups in terms of serum equol concentrations in an independent manner of soy-derived product intake among the study participants.

Influences of dietary soy isoflavones on metabolism but not nociception and stress hormone responses in ovariectomized female rats

BackgroundIsoflavones, the most abundant phytoestrogens in soy foods, are structurally similar to 17beta-estradiol. Few studies have examined the nociception and stress hormone responses after consumption of soy isoflavones.MethodsIn this study, ovariectomized (OVX) female Long-Evans rats were fed either an isoflavone-rich diet (Phyto-600) or an isoflavone-free diet (Phyto-free). We examined the effects of soy isoflavones on metabolism by measuring body weights, food/water intake, adipose tissue weights as well as serum leptin levels. Also, circulating isoflavone levels were quantified. During chemically induced estrous, nociceptive thresholds were recorded. Then, the animals were subjected to a stressor and stress hormone levels were quantified.ResultsBody weights were significantly lower in Phyto-600 fed rats compared to Phyto-free values within one week and during long-term consumption of soy isoflavones. Correspondingly, Phyto-600 fed animals displayed significantly less adipose deposition and lower serum leptin levels than Phyto-free values. However, rats on the Phyto-600 diet displayed greater food/water intake compared to Phyto-free levels. No changes in thermal pain threshold or stress hormone levels (ACTH and corticosterone) were observed after activation of the hypothalamic-pituitary-adrenal (HPA) stress axis.ConclusionIn summary, these data show that consumption of soy isoflavones 1) increases metabolism, demonstrated by significantly decreased body weights, adipose tissue deposition and leptin levels, but 2) does not alter nociception or stress hormone responses, as indexed by thermal pain threshold, serum corticosterone and ACTH levels in chemically-induced estrous OVX rats.

Analysis of phenolic compounds and isoflavones in soybean seeds (Glycine max (L.) Merill) and sprouts grown under different conditions

Soybeans (Glycine max (L.) Merill) are popularly known as a healthy food in many Asian countries and are mostly consumed as soymilk, tofu, and fermented products such as miso, temph, and sufu. The objective of this study was to determine the variation and composition of phenolic compounds and isoflavone contents in soybean seeds [Glycine max (L.) Merill] and sprouts [Kongnamul] grown under dark conditions (producing yellow soybean sprouts) and in green and yellow boxes (producing green soybean sprouts). In seven soybean cultivars, the total phenolic content ranged from 6.67 μg−1 in Pureunkong to 72.33 μg−1 in Poongsannamulkong. The average total phenolic content in the green soybean sprouts (48.33 μg−1) was higher than in the yellow soybean sprouts (29.75 μg−1). The total phenolic content in the yellow soybean sprouts varied from 9.88 μg−1 to 47.71 μg−1, and the total phenolic content in the green soybean sprouts varied from 29.21 μg−1 to 79.70 μg−1. Only four phenolic compounds, p-hydroxybenzoic acid, salicylic acid, p-coumaric acid, and ferulic acid, were detected in all soybean cultivars. Syringic acid was not detected in yellow soybean sprouts, and myricetin was only detected in yellow soybean sprouts (4.65 μg−1) from the Pureunkong cultivar grown under dark conditions. The total isoflavone content in soybean seeds ranged from 2.1 μg−1 in Sowonkong to 33.0 μg−1 in Pureunkong, and the mean total isoflavones was 10.61 μg−1. Green soybean sprouts had higher average total isoflavones (1389.4 μg−1) than yellow soybean sprouts (559.2 μg−1), and the total isoflavone content was highest in the Pureunkong yellow soybean sprouts (756.3 μg−1) and the Sowonkong green soybean sprouts (2791.6 μg−1). In soybean sprouts, the higher the (malonyl)-daidzin or (malonyl)-genistein content, the higher the total isoflavone level. Our study suggests that producing soybean sprouts enriched in isoflavones under coloured-light sources is feasible.

Effect of extraction methods and UHT treatment conditions on the level of isoflavones during soymilk manufacture

The objective of this study was to compare the effect of hot and cold grinding as well as the effect of direct and indirect ultra high temperature (UHT) treatment conditions on the level of isoflavones during the manufacture of soymilk. Soymilks were manufactured from dehulled soybeans by hot grinding or cold grinding processes. After inactivation of lipoxygenase at 85 °C, the resulting slurries were decanted and supernatants were held at 120 °C for 80 s to inactivate the trypsin inhibitor. The decanted soya bases were cooled and subjected to different temperature/time regimes by direct and indirect UHT treatments. Samples were drawn at different points in the processing operation and a reversed phase high performance liquid chromatography method was used to determine the concentration of isoflavones. Results showed that hot grinding caused a higher extraction of isoflavones into the soymilk than the cold-grinding process. However, direct or indirect heating in the UHT process did not significantly influence the concentration of isoflavones.

Effect of different coagulants on the isoflavone levels and physical properties of prepared firm tofu

The objective of this study was to understand the effect of different coagulants in their ability to retain isoflavones in prepared firm tofu. Harovinton beans were processed to obtain soymilk and a specific amount of this soymilk was coagulated using different types of coagulants for the preparation of tofu. A reversed phase high performance liquid chromatographic method was used for determining the concentration of isoflavones in tofu and whey. Quality parameters such as the texture, color and moisture of tofu, prepared from different coagulants were also determined in this study. Tofus coagulated with different coagulants were found to contain different amounts of isoflavones. Calcium sulfate was found to be the most suitable coagulant for tofu making in terms of its high yield, retention of maximum amount of isoflavones and in obtaining a firm, but not hard texture of tofu.

Red Clover Trifolium pratense L. Phytoestrogens: UV-B Radiation Increases Isoflavone Yield, and Postharvest Drying Methods Change the Glucoside Conjugate Profiles

Isoflavone extracts of red clover Trifolium pratense L. (cv. Pawera) with dissimilar glucoside conjugate profiles were obtained by employing different postharvest drying methods. The most prominent isoflavones found were formononetin and biochanin A and their corresponding glucosides and malonyl glucoside esters. Postharvest freeze drying inhibited the conversion of the glycosides to the aglycones, while vacuum drying allowed for maximum conversion of the glycosides to their corresponding aglycones. Air drying produced a low level of the aglycones formononetin and biochanin A, and oven drying promoted decarboxylation of the malonyl glucosides to the acetyl glucosides. Exposure to enhanced UV-B radiation resulted in an increase in total formononetin and biochanin A isoflavone levels, indicating that harvest during a period of high ambient UV-B radiation may be appropriate for maximum yield. The levels of caffeic acid and flavonols also increased by about 40 and 250%, respectively, on exposure to enhanced UV-B radiation.

‘Grasslands HF1’ red clover (Trifolium pratense L.)—a cultivar bred for isoflavone content

‘Grasslands HF1’ red clover was bred from the tetraploid cultivar ‘Grasslands Pawera’, with selection aimed at increasing the concentration of the isoflavone group, formononetin plus its glyco‐side ononin. Selection for two generations resulted in the concentration in leaves being raised to about 50% above that of ‘Pawera’, when harvested from sown rows. The level of total isoflavones increased by about 17%. The levels of three other isoflavone groups were not changed significantly during the selection of ‘HF1’ from ‘Pawera’. However, comparisons with the cultivar ‘Grasslands G27’ bred earlier from ‘Pawera’ for decreased level of formononetin, showed larger and more significant differences between these two extreme cultivars in the levels of most isoflavones.

Circulating levels of isoflavones and markers of 5α-reductase activity are higher in Japanese compared with New Zealand males: What is the role of circulating steroids in prostate disease?

Epidemiological evidence implicates dietary isoflavone intake as protective against prostate disease. A putative mechanism is attenuated circulating androgen levels in male populations consuming an isoflavone rich diet. We investigated this hypothesis by collecting plasma from 60 Japanese and 60 New Zealand males aged between 21 and 31 years each consuming their traditional diets. We measured plasma testosterone, dihydrotestosterone (DHT), androstenedione, dehydroepiandrosterone sulfate (DHEAS), the combined levels of androsterone sulfate and epiandrosterone sulfate (AoS/epiAoS), sex hormone-binding globulin, and cortisol and corticosteroid-binding globulin as well as the isoflavones genistein and equol. Plasma genistein and equol levels were several times higher in Japanese males as would be expected from an isoflavone rich diet. However, androstenedione, DHEAS, calculated free testosterone and paradoxically markers of 5α-reductase, DHT and AoS/epiAoS were all also significantly higher in Japanese rather than the New Zealand male counterparts. All other comparisons were not significant. Plasma DHT and DHEAS correlated positively with plasma equol and plasma AoS/epiAoS correlated positively with genistein levels. Taken together the results suggest that, rather than reduced levels of steroidogenesis, Japanese males may have increased 5α-reductase activity and possibly altered 17β OH steroid dehydrogenase activity. Significantly the positive association between isoflavones levels and 5α-steroids is counter-intuitive to isoflavone intake offering prostate protection, unless this is postulated to occur through other mechanisms.

Comparative effect of seeds of Rhynchosia volubilis and soybean on MG-63 human osteoblastic cell proliferation and estrogenicity

The seeds of Rhynchosia volubilis (SRV) (Leguminosae) and soybean have been used in oriental folk medicine to prevent postmenopausal osteoporosis. Their beneficial effects are caused by a high content of isoflavone, which function as partial agonists or antagonists of estrogen. To compare the estrogenic effects of SRV and soybean on the MG-63 osteoblastic cell proliferation, 70% methanol extracts of SRV or soybean were treated on MG-63 cells. Although biphasic over a concentration range of 0.001 mg/ml–0.1 mg/ml, both SRV and soybean extracts increased MG-63 cell proliferation. However SRV was more effective at increasing the cell proliferation that paralleled with the greater estrogenic effects as determined by estrogen receptor α (ERα) expression, an estrogenic response element (ERE)-luciferase activity and the selective expression of insulin-like growth factor-I (IGF-I). SRV-induced IGF-I expression resulted from increases in the mRNA levels. Despite the increased expression of ERβ, ERE activity and IGF-I expression by soybean were lower than those by SRV. Furthermore, the comparable estrogenic effects between SRV and the combined treatment of genistein and daidzein standards at 0.5 × 10 − 8 M, which is a concentration of these two isoflavones similar to that of SRV at 0.001 mg/ml, demonstrate that the greater estrogenicity of SRV for MG-63 cell proliferation is mediated by the synergism of low levels of isoflavones for the selective expression of IGF-I.

Isoflavone Conjugates Are Underestimated in Tissues Using Enzymatic Hydrolysis

Many health effects of soy foods are attributed to isoflavones. Isoflavones upon absorption present as free form, glucuronide, and sulfate conjugates in blood, urine, and bile. Little is known about the molecular forms and the relative concentrations of soy isoflavones in target organs. Acid hydrolysis or enzymatic hydrolysis (glucuronidases and sulfatases) was used to study isoflavone contents in the heart, brain, epididymis, fat, lung, testis, liver, pituitary gland, prostate gland, mammary glands, uterus, and kidney from rats fed diets made with soy protein isolate. The heart had the lowest isoflavone contents (undetectable), and the kidney had the highest (1.8 +/- 0.6 nmol/g total genistein; 3.0 +/- 1.1 nmol/g total daidzein). Acid hydrolysis released 20-60% more aglycon in tissues than enzymatic digestion (p < 0.05), and both hydrolysis methods gave the same level of isoflavones in serum. Approximately 28-44% of the total isoflavone content within the liver was unconjugated aglycon, and the remainder was conjugated mainly as glucuronide. The subcellular distribution of total isoflavones was 55-60% cytosolic and 13-16% in each of the nuclear, mitochondrial, and microsomal fractions. These results demonstrated that (1) soy isoflavones distribute in a wide variety of tissues as aglycon and conjugates and (2) the concentrations of isoflavone aglycons, which are thought to be the bioactive molecules, are in the 0.2-0.25 nmol/g range, far below the concentrations required for most in vitro effects of genistein or daidzein.

Protective actions of soy isoflavones and n-3 PUFAs on bone mass in ovariectomized rats

Ovariectomy (OVX) in female rats precipitates a marked reduction in endogenous estrogen concentrations and induces bone remodeling abnormalities that augment bone loss and increase the risk of developing osteopenia. This research examined the combined effects of two levels of soy isoflavones (IFs), trace (−IF) and high (+IF) (0.03 and 3.43 mg/g protein, respectively), and two levels of n-3 polyunsaturated fatty acids (PUFAs) on bone conservation in 2-month-old sexually mature OVX Sprague–Dawley rats. All dietary treatments provided 110.4 g/kg of fat from either safflower oil (N6) or a blend of safflower oil and menhaden oil (N3). OVX rats were randomly assigned to the N6−IF, N6+IF, N3−IF and N3+IF groups. The OVX and sham rats were euthanized after 12 weeks of feeding. Data for sequential femoral and tibial in vivo bone mineral density and bone mineral content (BMC) measurements were determined every 4 weeks. The hindlimb mineral data indicated a trend toward a positive bone mineral-sparing effect related to +IF. Among the OVX rats, those fed the N3+IF diet had a significantly higher value for tibial BMC. The concentration of serum pyridinoline cross-links was significantly lower in the N3+IF group. These findings indicate a complementary action of soy IFs and n-3 PUFAs for attenuating bone mineral reduction in OVX rats.

Bioavailability of isoflavone phytoestrogens in postmenopausal women consuming soya milk fermented with probiotic bifidobacteria

We investigated the effects of consuming an isoflavone aglycone-enriched soya milk containing viable bifidobacteria on urinary isoflavone excretion and percentage recovery. Sixteen postmenopausal women were randomly divided into two groups to consume either fermented or non-fermented soya milk. Each group participated in a double-blind, crossover study with three 14 d supplementation periods, separated by a 14 d washout. Subjects ingested three daily dosages of isoflavone via the soya milk and collected four 24 h pooled urine specimens per supplementation period. Soya milks were prepared with soya protein isolate and soya germ, followed by fermentation with bifidobacteria. Isoflavone levels were quantified using HPLC. Non-fermented soya milks at 20, 40 and 80 mg isoflavone/200 ml contained 10 %, 9 % and 7 % aglycone, respectively, with their fermented counterparts containing 69 %, 57 % and 36 % aglycone (P<0.001). A trend to a greater percentage urinary recovery of daidzein and glycitein was observed among women consuming fermented soya milk at a dosage of 40 mg isoflavone (P=0.13). A distinct linear dose response for the fermented soya milk group (R2=0.9993) compared with the non-fermented group (R2=0.8865) suggested less interindividual variation in isoflavone absorption. However, total urinary isoflavone excretion was similar for both groups (P>0.05), with urinary isoflavone recovery at approximately 31 %. Increasing the isoflavone dosage correlated positively with its urinary excretion, but urinary percentage recovery of isoflavone was inversely related to dosage level. Hence, a modest dosage ranging from 20 to 30 mg/d may provide the most bioavailable source of isoflavone, regardless of whether it is via an aglycone-rich fermented soya milk or a glucoside-rich soya milk.

Glyphosate-Tolerant Soybeans Remain Compositionally Equivalent to Conventional Soybeans (Glycine max L.) during Three Years of Field Testing

Previous studies have shown that the composition of glyphosate-tolerant soybeans (GTS) and selected processed fractions was substantially equivalent to that of conventional soybeans over a wide range of analytes. This study was designed to determine if the composition of GTS remains substantially equivalent to conventional soybeans over the course of several years and when introduced into multiple genetic backgrounds. Soybean seed samples of both GTS and conventional varieties were harvested during 2000, 2001, and 2002 and analyzed for the levels of proximates, lectin, trypsin inhibitor, and isoflavones. The measured analytes are representative of the basic nutritional and biologically active components in soybeans. Results show a similar range of natural variability for the GTS soybeans as well as conventional soybeans. It was concluded that the composition of commercial GTS over the three years of breeding into multiple varieties remains equivalent to that of conventional soybeans.

Comparative Effect of Soy Protein, Soy Isoflavones, and 17β-Estradiol on Bone Metabolism in Adult Ovariectomized Rats

This study provided a comprehensive investigation on the effect of soy protein and soy isoflavones on both calcium and bone metabolism in virgin adult rats. The measurements included bone histology, calcium kinetic modeling, calcium balance, bone densitometry, and whole body densitometry. Results confirmed the bone-preserving effect of estrogen but did not support a bone-sparing role of soy isoflavones. Several animal and short-term human studies have indicated that soy protein isolate enriched with isoflavones may be used as an alternative therapy to estrogen replacement therapy. However, none of the previous studies have investigated this estrogenic effect on both calcium and bone metabolism in animals or humans, which is essential in ascertaining the mode of action of isoflavones. This study was designed to determine the effects of soy protein versus isoflavones on calcium and bone metabolism in an ovariectomized rat model. Unmated 6-month-old ovariectomized and sham-operated female Sprague-Dawley rats were randomly assigned to nine groups (16 rats/group) and pair-fed soy- or casein-based diets with or without isoflavones for 8 weeks. A reference group was administered estrogen through subcutaneous implants (20-35 pg/liter plasma). Bone densitometry, histomorphometry, and mechanical testing were used to study bone metabolism and quality. Calcium metabolism was studied using calcium tracer balance and kinetics. After ovariectomy, estrogen prevented bone loss in trabecular bone and suppressed formation on both trabecular and cortical bone surfaces. Isoflavones given as enriched soy protein isolate or supplements did not prevent trabecular bone loss. Combining isoflavones with estrogen had no additional benefits over estrogen alone. There were no differences in response to isoflavones caused by protein source. None of the treatments significantly affected either total Ca balance or (45)Ca absorption. However, soy protein showed significant effects on reducing urinary loss of Ca in animals, irrespective of isoflavone level, perhaps because of the lower amount of sulfur-containing amino acids in soy protein. Estrogen, but not isoflavones at the levels tested, suppressed bone remodeling in both trabecular and cortical bone after ovariectomy.

Comparison of regulative functions between dietary soy isoflavones aglycone and glucoside on lipid metabolism in rats fed cholesterol

The effects of dietary soy isoflavones aglycone and glucoside on lipid metabolism were compared in male Sprague–Dawley rats (4 weeks old) given purified diets containing 0.3% cholesterol. The rats were fed a diet supplemented with either isoflavone aglycone-rich powder (IF-A group) or isoflavone glucoside-rich powder (IF-G group) or isoflavone-free diet (control group) for 40 days. The additional level of isoflavone aglycone moiety in the diet was prepared to the same level (approximately 0.096 g/100 g: approximately 0.1% in diet). The activity of hepatic cholesterol 7α-hydroxylase tended to be slightly higher in the rats fed isoflavones than in those fed the isoflavone-free diet. On the other hand, the activity of hepatic Δ6 desaturase in the IF-A group was lower than that of the control group. Reflecting this effect, the Δ6 desaturation indices [(20:3n-6+20:4n-6)/18:2n-6] in liver phospholipids of the IF-A group were lower than those in the control group. Liver and serum total cholesterol levels and liver TG level were also reduced by consumption of isoflavone aglycone. Moreover, serum TG level was lowered by consumption of both isoflavones aglycone and glucoside. The level of serum total isoflavones in the IF-A group was significantly higher than that in the IF-G group. Therefore, we speculate that the absorption speed of isoflavone aglycones might be faster than that of isoflavone glucosides in rats. This study suggests that dietary soy isoflavones, particularly their aglycone form, may exert a beneficial effect on lipid metabolism in rats fed cholesterol.

Antioxidant Properties of Soybean Isoflavone Extract and Tofu in Vitro and in Vivo

Isoflavones in soybean were extracted in the crude form using 80% food-grade ethanol at 80 degrees C for 6 h and followed by concentration and dehydration. The soy extract contained isoflavones primarily in the forms of glucosides. In vitro antioxidant activities of the soy extract containing 20-500 ppm isoflavones were conducted using a Rancimat method. The results showed that soy isoflavone extract had strong in vitro antioxidant activity. There was a dose-dependent response for the in vitro antioxidant activity at the lower concentrations but not at the higher concentrations. In vivo antioxidant property was determined by measuring the antioxidant enzymes, superoxide dismutase, and catalase in various organs of rats that were fed with diets containing partially oxidized oil and various levels of isoflavones for up to 24 weeks. Neither short-term (8 weeks) feeding nor low isoflavone content (50 ppm) induced changes in superoxide dismutase or catalase activities in rats. Only diets containing high isoflavone contents (150 and 250 ppm) showed obvious elevated enzymatic levels in various organs. In addition, a laboratory-prepared tofu containing approximately 50 ppm isoflavones had better effects than the soy extract with the 250 ppm isoflavone group, which indicated that molecules other than isoflavones may have a synergistic effect on in vivo antioxidant enzyme inductions of tofu.

Effect of Temperature, Elevated Carbon Dioxide, and Drought during Seed Development on the Isoflavone Content of Dwarf Soybean [Glycine max (L.) Merrill] Grown in Controlled Environments

The effects of elevated temperature, carbon dioxide, and water stress on the isoflavone content of seed from a dwarf soybean line [Glycine max (L.) Merrill] were determined, using controlled environment chambers. Increasing the temperature from 18 degrees C during seed development to 23 degrees C decreased total isoflavone content by about 65%. A further 5 degrees C increase to 28 degrees C decreased the total isoflavone content by about 90%. Combining treatments at elevated temperature with elevated CO(2) (700 ppm) and water stress to determine the possible consequences of global climate change on soybean seed isoflavone content indicated that elevated CO(2) at elevated temperatures could partially reverse the effects of temperature on soybean seed isoflavone content. The addition of drought stress to plants grown at 23 degrees C and elevated CO(2) returned the total isoflavone levels to the control values obtained at 18 degrees C and 400 ppm CO(2). The promotive effects of drought and elevated CO(2) at 23 degrees C on the 6' '-O-malonygenistin and genistin levels were additive. The individual isoflavones often had different responses to the various growth conditions during seed maturation, modifying the proportions of the principal isoflavones. Therefore, subtle changes in certain environmental factors may change the isoflavone content of commercially grown soybean, altering the nutritional values of soy products.

Quantification of Isoflavones in Soymilk and Tofu from South East Asia

The concentration and distribution of isoflavones in commonly used soybean foods were evaluated by high-performance liquid chromatography. The different forms of isoflavone glucoside esters were converted to their corresponding glucosides by a mild saponification of the extracts. Isoflavone levels were reported as microgram aglycone equivalents per gram of soy food. The total isoflavone concentrations in soymilk and tofu ranged from 76 to 199 µg/g and 162 to 312 µg/g respectively, on a wet weight basis. A comparison of isoflavone levels in soymilk and tofu, prepared by a standard procedure with the commercially available packaged soymilk and tofu samples were also carried out. Even though different types of tofu had different isoflavones concentrations, each type had similar values compared to those produced by the standard procedure.

Analysis of isoflavone concentration and composition in soybean [Glycine max (L.)] seeds between the cropping year and storage for 3�years

The objective of this study was to examine the relation between storage period and isoflavone concentration and composition in soybean [Glycine max (L.) Merrill] seeds. Total isoflavones varied from 470.0 to 878.1 µg g−1 over the three cropping years and there were significant differences between the soybean cultivars. Generally, the malonyl conjugates were in higher concentrations than were the other compounds, and the individual isoflavones varied with each cropping year. The Myeongjunamul (1998: 936.7 µg g–1, 1999: 727.0 µg g–1, 2000: 807.8 µg g–1) cultivar had the highest concentration, on average. Regarding changes in isoflavones with storage period, the concentration decreased by 91.7 to 171.1 µg g–1. Malonyldaidzin and malonylgenistin concentrations also decreased, and the concentration of glucosides increased slightly over the 3 years. Acetyldaidzin, acetylglycitin and glycitein could not be detected or were only found in very small concentrations. Pureun (−66.2 µg g–1) and Myeongjunamul (−77.4 µg g–1) cultivars showed little variation in isoflavone levels, whereas the concentration in Muhan (–295.4 µg g–1) decreased markedly on average over the three storage years. There were also significant differences between the cultivars. Our study suggests that it might be feasible to improve the storage methods of soybeans to preserve them for longer periods, which would have benefits for both their import and their export.