Science Snippets!

Soybeans (Glycine max L.) and soy products are rich in protein and isoflavones. There is a lot of discussion on the availability of isoflavones to the human and animal body. In order for a human body to absorb the isoflavones the isoflavone glucosides (e.g. daidzin, genistin, and glycitin) need to be hydrolyzed to aglycones (e.g. daidzein, genistein, and glycitein). In the human or animal body intestinal bacteria are important in isoflavone hydrolysis.

Chun et al. (2007) working from previous research on bio-availability of isoflavones, designed an interesting study. Chun et al. (2007) were particularly interested in four specific lactic acid bacteria (Lactobacillus paraplantarum KM, Enterococcus durans KH, Streptococcus salivarius HM, and Weissela confusa JY) and how efficient these bacteria hydrolyzed isoflavone glucosides to aglycones. The authors isolated the four lactic acid bacteria from humans. The isolated bacteria were started to get a cell count of 106 to 107 CFU/ml. Starting with the same cell populations ruled out any discrepancies in hydrolysis due to varying populations of the four bacteria. The four individual bacteria were added to four batches of identical soymilk and fermentation was allowed to take place for 12 h at 37°C. Samples were taken every three hours samples to monitor the fermentation progress. The authors took data on acid production (indication of fermentation), bacteria cell number, and isoflavone content. Isoflavones were identified and quantified by HPLC.

Chun et al. (2007) found that the initial pH of the soymilk (pH=6.3) dropped quickly within the first six hours to pH=4.6. Soymilk with the L. paraplantarum KM strain showed the lowest pH (pH=4.1) after 12 h. These data showed that fermentation took place relatively quickly.

The isoflavone profile changed over time during fermentation. Chun’s et al. (2007) research showed that, in general, isoflavones in the glucoside form changed to isoflavones in the aglycone form—e.g. daidzin changed to daidzein. In the soymilk with L. paraplantarum KM this change in isoflavone profile occurred already after 6 h. (Chun et al., 2007). For example, for soymilk with L. paraplantarum KM daidzin content from 353.9 µmol/100g to 31.9 µmol/100g after 12 h of fermentation, while the daidzein content increased from 87.1 to 517.0 µmol/100g. Genistin and glycitin and their aglycones showed similar trends after 12 h fermentation with L. paraplantarum K. Taken together, these data suggest that fermentation of soymilk with specific lactic acid bacteria might make isoflavones more available to the human and animal body by converting them efficiently in the aglycone form.

Chun et al. (2007) conclude that bacteria strain L. paraplantarum KM shows promise in the fermentation of soymilk due to its high capacity in isoflavone conversion, high growth rate and rapid fermentation.

Reference:
Chun, J., G.M. Kim, K.W. Lee, I. D. Choi, G-H. Kwon, J-Y. Park, S-J Jeong, J-S Kim, and J. H. Kim. 2007. Conversion of isoflavone glucosides to aglycones in soymilk by fermentation with lactic acid bacteria. Journal of Food Science. 72:M39-M44.