Isoflavone Composition, Phenol Content, and Antioxidant Activity of Soybean Seeds from India and Bulgaria G. SAKTHIVELU, † M. K. AKITHA DEVI, † P. GIRIDHAR, † T. RAJASEKARAN, † G. A. RAVISHANKAR,* ,† M. T. NIKOLOVA, § G. B. ANGELOV, § R. M. TODOROVA, # AND G. P. KOSTURKOVA ⊥ Plant Cell Biotechnology Department, Central Food Technological Research Institute, Mysore 570020, Karnataka, India; Institute of Botany and Institute of Genetics, Bulgarian Academy of Sciences, Sofia 1113, Bulgaria; and Institute of Forage Crops, NCAS, Pavlikeni 5200, Bulgaria Isoflavone levels and isoflavone chemical composition in 11 cultivars of soybean, including 4 Indian and 7 genotypes of soybean grown in Bulgaria, were analyzed as determined by C 18 reversed phase high-performance liquid chromatography coupled with a photodiode array detector. Antioxidant activity of soybean extracts was assessed using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, and total phenolic compounds (TPC) were determined by using Folin-Ciocalteu reagent. The range of total isoflavones (TI) was 558.2-1048.6 µgg -1 of soy in Indian cultivars, and it was 627.9-1716.9 µgg -1 of soy in the case of Bulgarian cultivars. The highest and lowest total isoflavone contents were observed for Maus-2 (1048.6 µgg -1 of soy) and Hardee (558.2 µgg -1 of soy), respectively, for the Indian cultivars, and they were observed for Boryara (1716.9 µgg -1 of soy) and Line 5 (627.9 µgg -1 of soy) for the Bulgarian genotypes. DPPH radical scavenging activity did not differ significantly among the cultivars and did not correlate with TI, whereas TPC correlated well with TI and weakly with DPPH. Malonylglucoside of all the aglycones, total genistein (TGin), and total daidzein (TDin) showed strong correlation with total isoflavones, whereas acetylglucoside and aglycone levels did not significantly correlate with total isoflavone. Profiling of soybean isoflavone is helpful in understanding the regulation of isoflavone biosynthesis for greater improved resistance of crops to disease and greater health benefits for humans. This comparative study of soybean cultivars grown in India and Bulgaria throws light on their composition and nutraceutical value. KEYWORDS: Soybean cultivars; isoflavones; antioxidant; HPLC INTRODUCTION Soybean is known to be a complete food as it contains proteins, fats, essential amino acids, and beneficial secondary metabolites such as isoflavones and phenolic compounds. Soybean seeds contain isoflavones, which are bioactive mol- ecules of low molecular weight, hydrophobic peptides, or fatty acid components that are known to influence the physiological state in animals as well as in humans. Epidemiological studies have shown that consumption of soybeans and soy products reduces the risk of human cancer, osteoporosis, and cardiovas- cular diseases (1–3). Isoflavones are structurally similar to naturally occurring estrogens and show promise in protecting against hormone-dependent cancers (4). Therefore, increased consumption of soybeans and their processed products may be beneficial in preventing the incidence of degenerative diseases. In addition, isoflavones belong to a group of active plant defense compounds known as phytoalexins and thereby act as a repellant against insect feeding and pathogenic fungi (5). Isoflavones are also involved in nodulation of leguminous plants by inducing the expression of nodulation genes in rhizobial bacteria during symbiosis (6). The three isoflavone aglycones, namely,, genistein, daidzein, and glycitein, are each present in four glucosidic forms in soybeans and soy foods (Figure 1). In soybean seeds, the isoflavones occur primarily in their storage form as malonyl glucosides, whereas significant levels of glucoside and low levels of aglycones and acetyl glucosides are present. Isoflavone contents and distribution in soybean seeds are often altered by many factors, including cultivar, tissue type, and growth conditions such as planting location, crop year, temperature, soil nutrition, and storage durations (7–9). Low temperatures and high precipitation during seed development have been * Corresponding author (e-mail pcbt@cftri.res.in; telephone +91- 0821-2516501; fax 91-821-2517233). † Central Food Technological Research Institute. § Institute of Botany, Bulgarian Academy of Sciences. ⊥ Institute of Genetics, Bulgarian Academy of Sciences. # Institute of Forage Crops. 2090 J. Agric. Food Chem. 2008, 56, 2090–2095 10.1021/jf072939a CCC: $40.75  2008 American Chemical Society Published on Web 02/27/2008