Phytochemicals in Soybeans

Bioactivity and Health Benefits

Yang Li, Baokun Qi, Yang Li, Baokun Qi

• Verlag: CRC Press
• Jahr: 2022
• ISBN:
  9781000533521
• Auflage: 1
• Thema: Technology & Engineering
• Thema: Food Science

Soybeans represent an excellent source of high-quality protein with a low content in saturated fat. They can be made into various foods, such as tofu, miso, breakfast cereals, energy bars, and soy cakes. Much research has been carried out on the positive health effects of soybeans, and increasing evidence shows that consumption of soybeans may reduce the risk of osteoporosis, have a beneficial role in chronic renal disease, lower plasma cholesterol, and decrease the risk of coronary heart disease.

Phytochemicals in Soybeans: Bioactivity and Health Benefits describes in detail the chemical characteristics of health-promoting components of soybeans and soybean products, their impacts on human health, and emerging technologies about soybean processing and new products. With 22 chapters containing the most recent information associated with soybean products, topics of the chapters include soybeans' role in human nutrition and health, their composition and physicochemical properties, action mechanism of their physiologic function, processing engineering technology, food safety, and quality control.

Key Features:

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• Promotes soybean products as functional food with advanced processing technology

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• Presents the basic research containing the experimental design, methods used, and a detailed description of the results.

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• Provides a systematic approach to the subject to facilitate a better comprehension of the subjects with illustrations and diagrams

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• Includes a comprehensive and up-to-date list of references

With contributions from authors around the world who are experts in their field, this book contains new information on the health impacts of soybean consumption, new product development, and alternative technologies of soybean processing, and will be useful for professors and researchers, as well as graduate and undergraduate students alike.

1 Health Perspectives on Soy Isoflavones

Mira Mikulić, Milica Atanacković Krstonošić, Darija Sazdanić, and Jelena Cvejić

DOI: 10.1201/9781003030294-1

Contents

1.1 Introduction

1.2 Mechanism of Action

1.2.1 Estrogenic and Anti-Estrogenic Activity

1.2.2 Antioxidant Activity

1.2.3 Anti-Inflammatory Activity

1.2.4 Other Mechanisms

1.3 Metabolism and Bioavailability

1.3.1 Bioactive Metabolites

1.3.2 Intestinal Microbiota Influence

1.4 Health Effects

1.4.1 Menopausal Symptoms

1.4.2 Cancer

1.4.3 Cardiovascular Disease

1.4.4 Osteoporosis

1.4.5 Cognitive Functions

1.4.6 Diabetes

1.4.7 Polycystic Ovary Syndrome

1.4.8 Skin

1.4.9 Other Effects

1.5 Sources and Exposure

1.5.1 Food

1.5.2 Dietary Supplements

1.5.3 Infant Formulas

1.6 Safety Aspects

1.6.1 Adverse Effects

1.6.2 Recommendations

1.7 Concluding Remarks

Acknowledgment

References

1.1 Introduction

Isoflavones represent a subclass of chemical compounds with estrogen-like activities, classified as phytoestrogens. They are usually found in different plant species of the Fabaceae family, being the most abundant in soybeans, red clover, alfalfa, kidney beans, chickpeas, or kudzu (Mortensen et al., 2009; Mazur et al., 1998). Soybeans (Glycine max [L.], Fabaceae) are generally considered the major source of isoflavones in the human diet (Messina et al., 2017).

Epidemiological investigations, especially in soy-consuming Asian countries, have provided much data relating to the interconnection between soy intake and lower incidence of certain chronic and hormone-dependent diseases (Messina, 2016; Applegate et al., 2018; Somekawa et al., 2001). The potential health benefits attributed specifically to soy isoflavones encompass cancer prevention and treatment, menopausal symptoms alleviation, as well as lowering the risk of osteoporosis, cardiovascular diseases, and some other chronic diseases (Messina, 2016; Xiao et al., 2017). The consumer interest in soy-based food products, as well as isoflavones-containing supplements, has increased significantly in recent decades. The reason is the higher awareness of a wide population related to the purported health benefits of isoflavones (Messina et al., 2017).

Isoflavones belong to a class of compounds called phytoalexins, which are synthesized and accumulated in plants during stress conditions, thus having a protective role (Boue et al., 2009). Furthermore, isoflavones are generated in plants by the same phenylpropanoid biosynthetic pathway as flavonoids. These compounds are synthesized from phenylalanine and four molecules of malonyl CoA through several reactions leading to a final formation of 3-phenyl-4H-1-benzopyran-4-one (3-phenylchromen-4-one IUPAC name) (Figure 1.1) (Barnes, 2010). Although nonsteroidal, such compounds bear remarkable similarity in structure to 17-β-estradiol and therefore are considered naturally occurring plant estrogens or phytoestrogens (Pilsakova et al., 2010).

FIGURE 1.1 General structure of isoflavones.

Soy isoflavones include three groups of compounds in four chemical forms: Aglycones genistein (5,7,4’-trihydroxyisoflavone), daidzein (7,4’-dihydroxyisoflavone) and glycitein (7,4’-dihydroxy-6-methoxyisoflavone); the corresponding 7-O-β-glucosides (genistin, daidzin, glycitin), malonyl glycosides (6’’-O-malonylgenistin, 6’’-O-malonyldaidzin, 6’’-O-malonylglycitin), and acetyl glycosides (6’’-O-acetylgenistin, 6’’-O-acetyldaidzin, 6’’-O-acetylglycitin) (Lee et al., 2004) (Figure 1.2).

FIGURE 1.2 Chemical structures of soy isoflavones: Aglycones, 7-O-β-glycosides, acetyl glycosides, and malonyl glycosides.

Total isoflavone content in soybeans varies greatly, and authors from different regions reported values from 0.4 up to 9.5 mg/g of soybean seed, with usual average values ranging from 1 to 4 mg/g (Chiari et al., 2004; Cvejić et al., 2009; Lee et al., 2003; Wiseman et al., 2002). Regarding the isoflavone composition, from 12 different isoflavones generally present in soybeans, malonyl daidzin and malonyl genistin are the compounds usually found in the highest concentration (Bursać et al., 2017; Cvejić et al., 2011). Malonyl forms are known to be dominant in raw and unprocessed seeds. Actually, it is reported that the sum of ß-glucosides and malonyl glucosides represents 90% or more of the total isoflavones (Bursać et al., 2017; Lee et al., 2010). Hence, the least present forms in soybeans are aglycons or acetyl glucosides. Among three isoflavone types (compounds derived from the same aglycone) present in soy, daidzeins, or genistens are the most abundant, while glyciteins are generally the least present isoflavone type (on average 5–15% of total isoflavones) (Cvejić et al., 2011; Tepavčević et al., 2010).

It is known that various factors like genotype, environmental factors, location, and crop season can influence this characteristic (Hoeck et al., 2000; Tsai et al., 2007; Riedl et al., 2007). Namely, genetic factors are recognized as the most important ones, and it is indicated that phytoestrogen content and composition in soy could be inheritable traits (Cvejić et al., 2011; Miladinović et al., 2019), implying that breeding of cultivars with desirable isoflavone concentration is possible.

1.2 Mechanism of Action

1.2.1 Estrogenic and Anti-Estrogenic Activity

The occurrence of plant-derived compounds that are able to exert estrogenic and anti-estrogenic activities has been known since the 1940s when it was observed that animals fed with isoflavone-rich subterranean clover developed symptoms of diverse reproductive disorders (Bennetts et al., 1946).

Even though isoflavones are non-steroidal compounds, due to their molecular structure and weight similar to endogenous estrogen (17ß-estradiol) (Figure 1.3), they are able to bind to estrogen receptors (ER) and therefore are referred to as estrogen-like molecules or diphenolic non-steroidal estrogens (Pilsakova et al., 2010).

FIGURE 1.3 Structural similarity of estradiol and genistein.

When discussing the structural similarity of isoflavones (e.g. genistein) to 17ß-estradiol, one of the usual presentations of genistein used for comparison is orientation A in Figure 1.3. Barnes (2010) suggested that the proper way of genistein orientation is actually B (Figure 1.3), according to results obtained by crystallographic study (Pike et al., 1999). A significant characteristic of isoflavones is the presence of a phenolic ring in the structure, which principally represents a prerequisite for binding to the estrogen receptors (Setchell, 1998).

Estrogen receptors are intranuclear binding proteins and members of the nuclear steroid receptor superfamily, which act as ligand-dependent transcription factors. There are two estrogen receptor subtypes, alpha and beta (ERα and ERβ). Estrogen receptor subtypes are highly homologous, with the overall homology of the proteins’ ligand binding sites being 55% (Kuiper et al., 1996). However, a divergence of a few amino acids of the receptors induces different affinities toward various ligands (Kuiper et al., 1997).

Upon binding to a ligand, ER undergoes conformational changes and dimerizes, allowing the receptor-ligand complex to attach to specific DNA regulatory sequences, the estrogen response elements (ERE) in the promoter region of target genes. Through this action, ER modulates the rate of transcription of various specific target genes (Kuiper et al., 1997; Zhao et al., 2008; Welboren et al., 2009).

In addition, ERα can bind indirectly to the DNA in the nonclassical pathway through binding to other transcription factors, such as specificity protein 1 (Sp1) or nuclear factor kappa b (NF-κB) (Welboren et al., 2009).

Isoflavones can bind to both estrogen receptor subtypes, alpha (ERα) and beta (ERβ), with significantly higher binding and transactivation affinity toward ERβ isoform (Kuiper et al., 1996; Kuiper et al., 1998; Hwang et al., 2006). Moreover, the structural features of isoflavone molecules, such as the particular position and number of hydroxyl groups, seem to govern the binding affinity rate. Particularly, the elimination of one hydroxyl group leads to the decreased binding affinity of daidzein compared to genistein (Kuiper et al., 1998).

Isoflavones exert dual biological function depending on coexisting estrogen concentrations since isoflavones compete with endogenous estrogen for binding to ER. At the physiologic levels of estrogen, binding of less potent isoflavones to ER represses full estrogen activity and therefore they act as antagonists. Furthermore, such an inhibitory...