Evaluation of the isoflavone and total phenolic contents of kefir-fermented soymilk storage and after the in vitro digestive system simulation

•The isoflavone aglycone content doubled after the in vitro simulation.•The total phenolic content increased ninefold after the in vitro simulation.•Kefir-fermented soymilk promoted an increase in the isoflavones and total phenolics.•The aglycone and total phenolic and the kefir did not change during storage of soymilk.

This study aimed to evaluate the isoflavone and total phenolic contents in kefir-fermented soymilk storage and after the in vitro digestive system simulation (DSS). Soymilk was fermented with kefir culture (0.02 UC/L) at 25 °C for 15 h and stored at 4 °C for 4 days. After the fermentation and storage, the isoflavone and total phenolic contents were quantified by high performance liquid chromatography and spectrophotometry, respectively. The cell viability of lactic acid bacteria and yeast was evaluated. Fermentation promoted an increase of approximately 3 log CFU/g cycles of the microorganisms and the storage process did not alter the aglycone isoflavones and total phenolic contents. The content of aglycone isoflavones increased 2-fold, and the total phenolic content increased 9-fold. Therefore, kefir-fermented soymilk is a good source of aglycone isoflavones and phenolics, since the content of these substances was increased significantly after the in vitro digestive system simulation of the product.