Daidzein and genistein content of fruits and nuts

doi:10.1016/S0955-2863(00)00085-1

The Journal of Nutritional Biochemistry

Volume 11, Issue 6, June 2000, Pages 326-331

https://doi.org/10.1016/S0955-2863(00)00085-1 Get rights and content

Abstract

Dietary phytoestrogens such as the isoflavones daidzein and genistein are thought to protect against chronic diseases that are common in Western societies, such as cancer, osteoporosis, and ischemic heart disease. In addition, there are concerns regarding the deleterious effects of hormone-like compounds, especially with respect to the development of infants. However, there is little information regarding the phytoestrogen content of foods, and therefore epidemiologic investigations of phytoestrogens are limited. As part of a study quantifying the consumption of phytoestrogens, the objective of this work was to assess the daidzein and genistein content of fruits and nuts commonly eaten in Europe. Eighty different fruits and nuts were sampled, prepared for eating, and freeze-dried. Daidzein and genistein were extracted from the dried foods, and the two isoflavones were quantified after hydrolytic removal of any conjugated carbohydrate. Completeness of extraction and any procedural losses of the isoflavones were accounted for using synthetic daidzin (7-O-glucosyl-4′-hydroxyisoflavone) and genistin (7-O-glucosyl-4′5-dihydroxyisoflavone) as internal standards. Of the 80 foods assayed, 43 contained no detectable daidzein or genistein, at a limit of quantification of 1 μg/kg dry weight of food. Nine foods contained more than 100 μg of the two isoflavones combined per kilogram wet weight, and 28 contained less than this amount. Currants and raisins were the richest sources of the isoflavones, containing 2,250 μg and 1,840 μg of the two isoflavones combined per kilogram of wet weight of food. Although fruits and nuts are not as rich in isoflavone phytoestrogens as are soy and other legumes, this is the first documentation of levels of daidzein and genistein occurring in these foods.

Introduction

Daidzein and genistein are isoflavones that form part of a diverse group of natural constituents of foods, which, because of their estrogenic activity in humans, are known as phytoestrogens. Phytoestrogens bear a structural resemblance to 17β-estradiol, and in vivo can interfere with mechanisms controlled by the hormone through competition for its receptors. In addition, phytoestrogens can have nonestrogen receptor mediated effects. Phytoestrogens may be important antioxidants.1, 2 They perturb the action of DNA topoisomerase II and ribosomal S6 kinase, which could explain their observed effects on cell cycle, differentiation, proliferation, and apoptosis. In addition, genistein is a potent tyrosine kinase inhibitor.3, 4 It has been proposed that through such mechanisms phytoestrogens protect against a wide range of ailments including breast, prostate, bowel, and other cancers, cardiovascular disease, osteoporosis, and menopausal symptoms.3, 5, 6, 7, 8, 9 However, apart from soy and a few other legumes, little is known of the phytoestrogen content of foods.7, 10 As part of our work to determine the levels of phytoestrogens in foods, we report here the concentrations of daidzein and genistein in a variety of fruits and nuts commonly eaten in Europe.

The method used to assay fruits and nuts for daidzein and genistein has been published previously.11 It was developed using mixtures of bleached white wheat flour and soy flour with a known isoflavone composition. Daidzein and genistein are present in soy mainly as three types of glycosidic conjugate, linked either to glucose, malonyl, or acetyl derivatives of glucose. However, it is likely that other carbohydrate residues are linked in substitution of the glucose and that positions other than the carbon seven hydroxyl group of the isoflavone are used for a glycosidic bond. The carbohydrate component of the isoflavones is removed by the action of bacteria in the gut, producing the aglycones and other metabolites. Therefore, measurement of the total daidzin and genistin (the glucose derivatives) content of a food may underestimate the total daidzein and genistein content of a food after digestion and bacterial action. The assay procedure used in this article employs enzymes from Aspergillus niger, collectively known as cellulase, to hydrolyze the glycosidic bond and yield the aglycones daidzein and genistein. We have previously shown that this enzyme preparation works quantitatively with the various glycosides present in soya, and in the absence of knowledge of the identity and possession of reference standards of other glycosides, we have assumed that it hydrolyzes these with equal efficiency.11 The data on the concentration of daidzein and genistein in foodstuffs reported in this article can be used in epidemiologic studies to assess the dietary intake of these compounds.

Section snippets

Collection and preparation of food samples

Representative samples of each food were obtained by purchasing five samples of each from different sources in the Cambridge area, typically two market stalls and three supermarkets. The food was weighed, and any inedible matter was removed, weighed, and discarded. If the food was normally eaten raw, each sample was placed in separate sealed plastic bags and frozen at −20°C on the day of purchase for later freeze drying. Freeze drying typically took 1 week or more. Thereafter the samples were

Results

Eighty examples of fruits and nuts were analyzed for their daidzein and genistein content, of which 36 contained measurable quantities. In addition, raspberry tinned in syrup contained trace quantities of the isoflavones, but due to interference by other compounds these could not be measured. Table 1 shows the daidzein and genistein content of all foods (by both dry and wet weight) corrected for losses of the internal standards. The foods are listed in the order of the codes given in Holland et

Discussion

The foods selected for this study were chosen because they are common items in the European diet. There are no other published values for the amounts of daidzein and genistein in fruits and nuts. Published analytical data relating to the concentration of phytoestrogens is in the most part restricted to a small number of foods, most of which are relatively rich sources. Sources of low concentrations of phytoestrogens may be more common in particular dietary combinations, and cumulatively the low

Acknowledgements

The authors would like to thank the following people for their technical assistance: Mrs. M. Harding, Mr. K. Jones, Miss N. Duffy, Miss E. Neeley, Miss C. Jeffray, Miss L. Keppel, Miss A. Lam, and Miss S. Barker.

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^☆: This work was supported by the United Kingdom Medical Research Council, Ministry of Agriculture Fisheries and Food (contract FS2034), and the United States Army (contract DAMD17-97-1-7028).

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Research communicationDaidzein and genistein content of fruits and nuts☆

Abstract

Introduction

Section snippets

Collection and preparation of food samples

Results

Discussion

Acknowledgements

J. Biol. Chem.

Anal. Biochem.

J. Nutr. Biochem.

Antioxidant activity of phytoestrogenic isoflavones

Free Radic. Res.

Antioxidant and antipromotional effects of the soybean isoflavone genistein

Proc. Soc. Exp. Biol. Med.

Dietary phytoestrogens

Annu. Rev. Nutr.

Soy intake and cancer riskA review of the in vitro and in vivo data

Nutr. Cancer

Short-term effects of phytoestrogen-rich diet on postmenopausal women

Menopause

Phyto-oestrogens and Western diseases

Ann. Med.

Research communication
Daidzein and genistein content of fruits and nuts☆