Optimization of the Bioactivation of Isoflavones in Soymilk by Lactic Acid Bacteria

Jon Kepa Izaguirre,Itziar Alkorta,Luis M Quirós,Leire Barañano,Sonia Castañón,Carlos Garbisu

doi:10.3390/pr9060963

Abstract

Soybeans and soy-based products contain isoflavones which can be used for nutraceutical and medical applications. In soybeans and in unfermented soy foods, isoflavones are normally present as glycosides. Isoflavone glycosides can be enzymatically converted to isoflavone aglycones, thus releasing the sugar molecule. The effective absorption of isoflavones in humans requires the bioconversion of isoflavone glycosides to isoflavone aglycones through the activity of the enzyme β-glucosidase. The objective was to assess the capacity of 42 bacterial strains (belonging to Lactobacillus, Streptococcus and Enterococcus) to produce β-glucosidase activity. The strain that showed the highest β-glucosidase activity (Lactobacillus plantarum 128/2) was then used for the optimization of the bioconversion of genistin and daidzin present in commercial soymilk to their aglycone forms genistein and daidzein. The contribution of process parameters (temperature, inoculum size, time) to the efficiency of such bioactivation was tested. Lactobacillus plantarum 128/2 was able to completely bioactivate soymilk isoflavones under the following conditions: 25 °C temperature, 2% inoculum size and 48 h process time. These results confirm the suitability of lactic acid bacteria for the bioactivation of isoflavones present in soymilk and provide an interesting candidate (L. plantarum 182/2) for food industries to perform this transformation.

Highlights

Isoflavones are a group of flavonoids similar in structure and biological activity to endogenous 17β-estradiol [1]
The consumption of isoflavones has long been linked to a variety of health benefits such as, for instance, lower risk of cardiovascular disease and breast and prostate cancer, attenuated menopausal symptoms, prevention of bone loss, osteoporosis, etc. [1,3,4,5]
Isoflavones have been reported as potential endocrine disruptors and, with the capacity to cause adverse effects on human health [5,6]

Summary

Introduction

Isoflavones are a group of flavonoids similar in structure and biological activity to endogenous 17β-estradiol [1] Due to this structural similarity to the human female hormone 17β-estradiol, isoflavones can bind to estrogen receptors and show estrogen-like activities. There are growing concerns about an excessive exposure of humans to isoflavones owing to their estrogen-like properties [7,8]. At this time, there seems to be a consensus regarding the need for more studies on this issue, in order to confirm, rule out or put into context the potential health benefits (possibly, modest effects) linked to the consumption of soy isoflavones [2,9]

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Conclusion