Occurrence of isoflavones in soybean sprouts and strategies to enhance their content: A review

The pH acidity and nitrate accumulation by plasma discharge enhanced the growth and phytochemicals of soybean sprouts grown in reused water

This study investigated the effect of plasma treatment on reused water and evaluated the interactions of the plasma-treated water (PTW) with plants or microbes to determine the optimal PTW for reuse. The repeated treatment gradually accumulated nitrate (NO3-) in the PTW and lowered its pH; afterward, it led to the sprouted soybeans accumulating other inorganic ions in the PTW. The biomass of soybean sprouts was enhanced by the accumulated NO3- but decreased due to the pH effect. Meanwhile, the acidic pH reduced the microbial counts, but they increased after sprinkling the PTW over the sprouts. The optimal PTW in our study, which had a gradual increase of NO3- (≤321.8 mg·L-1) with an acceptable pH (≥pH 3), significantly enhanced the biomass by 4.2% compared to the untreated control. Additionally, it increased the total content of amino acids and isoflavones by 9% and 18% in the growing part, respectively.

Influence of malting procedure on the isoflavonoid content of soybeans

The goal of this study was to analyse, whether malting technique (consisting of seed hydration, germination and drying) can be used to modify concentration of various isoflavonoids in soybean seeds. Seeds of three soybean varieties were germinated by different lengths of time (from 24 to 120 h) and dried by two different methods, typically used to produce so-called 'light' and 'caramel' malts. It was determined, that malting decreases concentration of 7-O-β-D-glucosides such as daidzin, genisitin and glycitin, while at the same time increasing concentration of aglycones (daidzein, genistein and glycitein). Increasing time of the germination period increased concentration of aglycones. 'Caramel' type malts were characterised with higher concentration of most of the isoflavonoids (daidzin, daidzein, genistin, genistein and glycitein) than 'light' type malts. Results of this study suggest that soybean malts can be an interesting substrate in the production of various food products with increased aglycone content.

Evaluation of Total Isoflavones in Chickpea (Cicer arietinum L.) Sprouts Germinated under Precursors (p-Coumaric Acid and L-Phenylalanine) Supplementation

Cicer arietinum L. (Bengal gram, chickpea) is one of the major pulse crops and an important part of traditional diets in Asia, Africa, and South America. The present study was conducted to determine the changes in total isoflavones during sprouting (0, 3, and 7 days) along with the effect of two precursor supplementations, p-coumaric acid (p-CA) and L-phenylalanine (Phe), in C. arietinum. It was observed that increasing sprouting time up to the seventh day resulted in ≈1282 mg 100 g-1 isoflavones, which is approximately eight times higher than chickpea seeds. The supplementation of Phe did not affect the total length of sprouts, whereas the supplementation of p-CA resulted in stunted sprouts. On the third day of supplementation with p-CA (250 mg L-1), the increase in the total phenolic content (TPC) (80%), daidzein (152%), and genistin (158%) contents were observed, and further extending the supplementation reduced the growth of sprouts. On the seventh day of supplementation with Phe (500 mg L-1), the increase in TPC by 43% and genistin content by 74% was observed compared with non-treated sprouts; however, the total isoflavones content was found to be 1212 mg 100 g-1. The increased TPC was positively correlated with the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity (r = 0.787) and ferric-reducing antioxidant potential (FRAP) (r = 0.676) activity. This study suggests that chickpea sprouts enriched in TPC and antioxidants can be produced by the appropriate quantity of precursor supplementation on a particular day. The results indicated major changes in the phytochemical content, especially daidzein and genistin. It was also concluded that the consumption of 100 g of seventh-day sprouts provided eight times higher amounts of isoflavones in comparison to chickpea seeds.

Red and blue light-specific metabolic changes in soybean seedlings

Red and blue artificial light sources are commonly used as photosynthetic lighting in smart farm facilities, and they can affect the metabolisms of various primary and secondary metabolites. Although the soybean plant contains major flavonoids such as isoflavone and flavonol, using light factors to produce specific flavonoids from this plant remains difficult because the regulation of light-responded flavonoids is poorly understood. In this study, metabolic profiling of soybean seedlings in response to red and blue lights was evaluated, and the isoflavone-flavonol regulatory mechanism under different light irradiation periods was elucidated. Profiling of metabolites, including flavonoids, phenolic acids, amino acids, organic acids, free sugars, alcohol sugars, and sugar acids, revealed that specific flavonol, isoflavone, and phenolic acid showed irradiation time-dependent accumulation. Therefore, the metabolic gene expression level and accumulation of isoflavone and flavonol were further investigated. The light irradiation period regulated kaempferol glycoside, the predominant flavonol in soybeans, with longer light irradiation resulting in higher kaempferol glycoside content, regardless of photosynthetic lights. Notably, blue light stimulated kaempferol-3-O-(2,6-dirhamnosyl)-galactoside accumulation more than red light. Meanwhile, isoflavones were controlled differently based on isoflavone types. Malonyl daidzin and malonyl genistin, the predominant isoflavones in soybeans, were significantly increased by short-term red light irradiation (12 and 36 h) with higher expressions of flavonoid biosynthetic genes, which contributed to the increased total isoflavone level. Although most isoflavones increased in response to red and blue lights, daidzein increased in response only to red light. In addition, prolonged red light irradiation downregulated the accumulation of glycitin types, suggesting that isoflavone's structural specificity results in different accumulation in response to light. Overall, these findings suggest that the application of specific wavelength and irradiation periods of light factors enables the regulation and acquisition of specialized metabolites from soybean seedlings.

Identification of New Fusarium sulawense Strains Causing Soybean Pod Blight in China and Their Control Using Carbendazim, Dipicolinic Acid and Kojic Acid

Soybean plants are highly susceptible to Fusarium species, which significantly reduce soybean production and quality. Several Fusarium species have been reported to synthesize mycotoxins, such as trichothecene, which have been related to major human diseases. In November 2021, soybean pods in Nantong municipality, China, showed black necrotic lesions during the harvest stage. The disease incidence reached 69%. The pathogen was identified as Fusarium sulawense via morphological analysis and sequencing of ITS, EF1-α and RPB2 genes. A PCR assay with primers targeting the trichothecene biosynthesis genes suggested that the three isolates could synthesize trichothecenes. The effectiveness of fungicide carbendazim and natural metabolites dipicolinic acid and kojic acid was screened for the management of F. sulawense on postharvest soybean pods. The highest efficacy was obtained when combining 3.8 mg/mL carbendazim and 0.84 mg/mL dipicolinic acid (curative efficacy: 49.1% lesion length inhibition; preventive efficacy: 82.7% lesion length inhibition), or 1.9 mg/mL carbendazim and 0.71 mg/mL kojic acid (preventive efficacy: 84.9% lesion length inhibition). Collectively, this report will lead to a better understanding of the safety hazards found in soybean products in China and reveals the application of dipicolinic and kojic acids to reduce the use of carbendazim.

In the Search for Novel, Isoflavone-Rich Functional Foods—Comparative Studies of Four Clover Species Sprouts and Their Chemopreventive Potential for Breast and Prostate Cancer

Despite a significant amount of research, the relationship between a diet rich in isoflavones and breast and prostate cancer risk is still ambiguous. The purpose of the current study was to pre-select the potential candidate for functional foods among red, white, crimson, and Persian clover sprouts, cultured for different periods of time (up to 10 days), with respect to the isoflavone content (determined by HPLC-UV-VIS), and to verify their impact on hormone-dependent cancers in vitro. The red clover sprouts were the richest in isoflavones (up to 426.2 mg/100 g dw), whereas the lowest content was observed for the crimson clover. Each species produced isoflavones in different patterns, which refer to the germination time. Hormone-insensitive MDA-MB-231 breast cancer cells were more resistant to the tested extracts than estrogen-dependent MCF7 breast cancer cells. Regarding prostate cancer, androgen-dependent LNCap cells were most susceptible to the tested sprouts, followed by androgen-insensitive, high metastatic PC3, and low metastatic DU145 cells. The observed cytotoxic impact of the tested sprouts is not associated with isoflavone content, as confirmed by chemometric analysis. Furthermore, the sprouts tested revealed a high antioxidant potential, and were characterized by high safety for normal breast and prostate cells.