Plants isoflavones

Fig. 54.3 Aggregate artificial biosynthetic pathway for plant isoflavone 13 production Ifom fiavanones 12 in microorganisms...

In plants, isoflavones play major roles in the defense response to pathogen attack (Rivera-Vargas et al., 1993), and in nodulation and nitrogen fixation (Pueppke, 1996). Isoflavones also impart negative taste components to foods (Okubo et al., 1992) and the reduction of isoflavone concentrations would be of value for other products. A benefit of manipulating isoflavone concentrations is that increased levels of isoflavones may increase resistance to various pathogens (Padmavati and Reddy,... 

In plants and, consequently, in soy food products, isoflavones occur in three main biologically active forms ... 

To obtain an updated set of data on the phytoestrogens content in foods and diets, we suggest checking the following websites http //www.venus-ca.org/database.htm (phytoestrogen database of the EU-funded project VENUS) http //www.nal.usda.gov/fhic/foodcomp/Data/isoflav/isoflav.html (USDA-Iowa State University database on the isoflavones content of foods) and http //www.ilf.bbsrc.ac.uk/phytochemicals/Links.htm (Institute of Food Research Database on the levels of bioactive compounds in plant foods). 

YU o, JUNG w, SHI J, CROES R A, FADER G M, MCGONIGLE B and ODELL J T (2000) Production of the isoflavones genistein and daidzein in non-legume dicot and monocot tissues. Plant Physiol. 124 (2) 781-94. 

Many higher plants synthesize flavanes, flavanones, flavones, and isoflavones with a wide range of structural complexity. They make a significant contribution to the food intake of both herbivores and humans, and they have aroused particular interest on account of their degradation by mammals that are mediated by intestinal bacteria. Most of them exist naturally as glycosides and these are readily hydrolyzed to the aglycones. 

Now that an haustorial inducing factor has been characterized in a host plant that could be grown in the laboratory, the levels of the compounds actually exuded could be analyzed. John Steffens and Rody Spivey focused on developing methods that would allow for suitable quantitation. Efforts were made to quantitate not only the terpenoid components, but also the flavanoid, genistein (4, 5,7-trihydroxyiso-flavone), which was found to be a major isoflavone of Lespedeza. Genistein was analyzed to gain an estimate of levels of phenylpro-... 

Leonard, E. and Koffas, M.A. (2007) Engineering of artificial plant cytochrome P450 enzymes for synthesis of isoflavones by Escherichia coli. Applied and Environmental Microbiology, 73, 7246—7251. 

Food and plant phenolics are commonly detected using DAD detectors (Tan and others 2008). Photodiode array detection allows collection of the entire UV spectrum during the elution of a chromatographic peak, which makes it possible to identify a phenolic compound by its spectra. Simple phenols, phenolic acids, flavanones, benzophenones, isoflavones, and flavan-3-ols have maximum absorbance at 280 nm, hydroxycinnamic acids at 320 nm, flavonols, flavones, and dihydroflavonols at 365 nm, and anthocyanins at 520 nm (Ibern-G6mez and others 2002 Merken Hand Beecher 2000). Hydrolyzable tannins show a characteristic shoulder at 300 nm, suitable for identifying them (Arapitsas and others 2007). For stilbenes, maximum absorbance of trans-forms are at 306 nm and at 285 nm for cA-forms (Lamuela-Raventos and others 1995). 

Cheng H, Yu O and Yu D. 2008. Polymorphisms of IFS1 and IFS2 genes are associated with isoflavone concentrations in soybean seeds. Plant Sci 175 505-512. 

Phytoestrogens are a diverse group of polyphenolic non-steroidal plant compounds that bind to human estrogen receptors (Cos et al., 2003). The best studied of these compounds are the isoflavones, the phytoestrogens present in soy and red clover. 

Red clover is a plant that contains isoflavones in a slightly different composition compared with soy. Red clover contains formononetin and biochanin A, which are not present in soy and may thus have additional biological activity. So far, four studies (Barber et ah, 1999 Knight et ah, 1999 van de Weijer, 2002 Tice et ah, 2003) have been performed using isoflavones derived from red clover (Table 4.3). These have used doses of isoflavones ranging from 40 to 160 mg. Three out of four of these studies did not show any effects, even in spite of a very large sample size (Tice et ah, 2003). Only one study showed a reduction in the number of hot flushes. The reduction, however, was small (van de Weijer and Barentsen, 2002). Red clover therefore does not appear to have much of an effect on the reduction of hot flushes. 

While fiavonoids have the 2-phenylchromen-4-one backbone, isoflavonoids (Fig. 8) have the 3-phenylchromen-4-one backbone, with no hydroxyl substitution at position 2 in the case of isofiavones. In contrast with the parent class of fiavonoids, the distribution of the isoflavonoid class in the plant kingdom is relatively limited, probably owing to the sporadic occurrence of isoflavone synthase. Isoflavonoids... 

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