The principal chemical forms of isoflavones in soybean are their 6''-O-malonyl-beta-glucoside (6OMalGlc) conjugates. Experiments were carried out to determine the best conditions for extraction of isoflavones from soyfoods and the effects of commercial processing procedures and of cooking on isoflavone concentrations and composition. Hot alcohol extraction of ground soybeans deesterified 6OMalGlc conjugates. Although room temperature extraction slowed the conversion, extraction at 4 degrees C for 2-4 h led to the highest yield of 6OMalGlc conjugates and the lowest proportion of beta-glucoside conjugates. Analysis of soyfood products by reversed-phase HPLC-mass spectrometry revealed that defatted soy flour that had not been heat treated consisted mostly of 6OMalGlc conjugates; in contrast, toasted soy flour contained large amounts of 6''-O-acetyl-beta-glucoside conjugates, formed by heat-induced decarboxylation of the malonate group to acetate. Soymilk and tofu consisted almost entirely of beta-glucoside conjugates; low-fat versions of these products were markedly depleted in isoflavones. Alcohol-washed soy-protein concentrates contained few isoflavones. Isolated soy protein and textured vegetable protein consisted of a mixture of all 3 types of isoflavone conjugates. Baking or frying of textured vegetable protein at 190 degrees C and baking of soy flour in cookies did not alter total isoflavone content, but there was a steady increase in beta-glucoside conjugates at the expense of 6OMalGlc conjugates. The chemical form of isoflavones in foods should be taken into consideration when evaluating their availability for absorption from the diet.

Soy and its isoflavones are associated with a reduced risk of chronic disease. The mechanisms of action of isoflavones include their roles as weak estrogens, inhibitors of tyrosine kinase-dependent signal transduction processes and as cellular antioxidants. Although estrogen receptor beta binds genistein with an affinity close to that of 17beta-estradiol, it remains to be determined whether it is a mediator of genistein's activity in vivo. Genistein's inhibition of protein tyrosine kinases is not limited to direct effect on these kinases, but may result from alteration in kinase expression. Genistein is not a particularly good scavanger of cellular oxidants; however, it reacts vigorously with the prooxidant hypochlorous acid, produced by neutrophils as part of the inflammatory response. The chlorinated isoflavones may have altered biochemical and biological effects compared to their parent compounds and may provide increased protection against inflammatory disease.

Purpose: We performed a randomized double-blind crossover pilot study in elderly men with elevated prostate specific antigen (PSA) on the effects of the daily consumption of 2 soy beverages, each containing 20 gm. of isolated soy protein, on the isoflavone concentration in blood and urine, and on the 3 serum biomarkers cholesterol, PSA and the soluble p105 component of the p185erbB-2 proto-oncogene.Materials and Methods: A total of 34 men supplemented their diet by consuming 1 of 2 soy protein beverages assigned randomly twice daily for a 6-week period. In a second 6-week period they consumed the other soy protein beverage. The beverage ISPϩ provided 42 mg. of genistein and 27 mg. of daidzein daily, whereas the other beverage, ISPϪ, provided only 2.1 and 1.3 mg. of these isoflavones daily, respectively. Blood and 24-hour urine samples were obtained before the study, at 2-week intervals during the study and 2 weeks after study completion.Results: ISPϩ and to a lesser extent ISPϪ substantially increased the serum concentration and urinary output of the isoflavones and their metabolites. Serum cholesterol was significantly decreased by ISPϩ irrespective of the order in which the 2 soy beverages were administered and in apparent correlation with the total isoflavone concentration. There was no significant effect of the soy beverages on serum PSA and p105erbB-2 values.Conclusions: This study reveals that short-term exposure of elderly men with elevated serum PSA values to soy protein containing isoflavones decreases serum cholesterol but not the serum biomarkers PSA and p105erbB-2.KEY WORDS: prostate, prostate-specific antigen, soy proteins, biological markers, isoflavones Carcinoma of the prostate is a major health problem in American men. In 1998 there were more than 184,500 newly diagnosed cases and more than 39,000 deaths.1 Because there is no curative therapy for advanced prostate cancer, recent interest has focused on prostate cancer prevention. Several lines of evidence imply that dietary alterations in American men may decrease the risk for and incidence of prostate cancer. While it has been speculated that a diet with less than 30% fat may result in a decreased risk of prostate cancer, others believe that compliance with such a low fat diet would be poor. Other epidemiological studies indicate that the level of dietary soy consumption may be linked to a decreased risk of prostate cancer.2, 3 Soy contains large quantities of the isoflavone genistein (5,7,4í-trihydroxyisoflavone), a compound that is not present in other parts of the American diet ( fig. 1). 4 Men in southeast Asia, who consume 20 to 50-fold more soy daily than American men, have a 10-fold lower incidence of clinically significant prostate cancer and prostate cancer related death. 5,6 Thus, it has been hypothesized that American men may decrease the risk of prostate cancer by altering their diet to consume a higher level of soy proteins and, hence, genistein. 6Evidence that genistein is capable of inhibiting the human prostate growth wa...

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