Abstract

In the present study, soymilk is fermented with lactic acid bacteria (Streptococcus thermophilus BCRC 14085, Lactobacillus acidophilus BCRC 14079) and bifidobacteria (Bifidobacterium infantis BCRC 14633, B. longum B6) individually, and in combination. The change in the content of various isoflavones (aglycones, glucoside, acetyl- and malonyl-glucosides) and the β-glucosidase activity in soymilk during fermentation is investigated.

It is observed that fermented soymilk contains a lower total isoflavone content (81.94–86.61 μg/ml) than soymilk without fermentation (87.61 μg/ml). Regardless of starter organism employed, fermentation causes a major reduction in the contents of glucoside, malonylglucoside and acetylglucoside isoflavones along with a significant increase of aglycone isoflavones content. The level of change in the content of various isoflavones and β-glucosidase activity after fermentation varies with the starter organism. Among all the fermented soymilks tested, soymilk fermented with S. thermophilus showed the highest β-glucosidase activity and the greatest increase in the contents of aglycones. The percentage of daidzein, genistein and glycitein to total isoflavone content in S. thermophilus-fermented soymilk increases from an initial 14.24%, 6.89% and 2.45%, respectively, to 36.20%, 28.80% and 12.44% after 24 h of fermentation. Finally, the increase of aglycones and decrease of glucoside isoflavones during fermentation coincides with the increase of β-glucosidase activity observed in fermented soymilk.

Keywords: Fermented soymilk; Isoflavone; Lactic acid bacteria; Bifidobacteria

Article Outline

1. Introduction

2. Material and methods

2.1. Starter organism, preparation and fermentation of soymilk

2.2. Extraction of isoflavones from soymilk

2.3. HPLC analysis

2.4. Assay of β-glucosidase activity

2.5. Statistical analysis

3. Results and discussion

3.1. Isoflavones content in soymilk fermented with various lactic acid bacteria and bifidobacteria

3.2. Changes of isoflavone content during fermentation

3.3. β-Glucosidase activity in fermented soymilk

3.4. Changes of β-glucosidase activity, aglycone and glucoside isoflavone contents during fermentation

4. Conclusion

Further Reading

References