Effects of Tempeh Fermentation on Soy Free and Bound Phenolics: Release, Transformation, and Stimulated Production

The fermentation of tempeh, a traditional source of protein originated in Indonesia, has been reported to enhance the health-promoting potentials of various grains, legumes, and beans. Tempeh fermentation on soybeans can modulate the bioavailability of phenolic compounds, particularly isoflavones, bioactive compounds that have been found to be protective against lung, prostrate, and colon cancers. However, the mechanism of the protective benefits was unknown. Using whole-food and in vitro models, this study addressed this research gap by investigating the effects of tempeh fermentation using various cultures on the compositions of soy free, bound, and minor phenolics, as well as their antioxidative, anti-inflammatory, and anticancer activities. These parameters were assessed using high-resolution liquid chromatography-mass spectrometry (LC-MS) analysis using Folin-Ciocalteu method, nitric oxide test on RAW 264.7 murine macrophage cells, and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test on HCT 116 human colorectal carcinoma cells, respectively. Phenolic extracts obtained using ethyl acetate extraction were used. Whole-food fermentation was conducted using 105 CFU of tempeh culture spores for every 100 g of soybeans. In vitro fermentation was conducted using 105 CFU of tempeh culture spores in every 1 mL of potato dextrose broth. The incubation settings for both models were 30°C for 30 h. Tempeh fermentation showed activities that modulate soy antioxidative, anti-inflammatory, and anticancer activities, as well as the compositions of soy free, bound, and minor phenolics in phenolic extracts. In the cases of increased phenolic content and bioactivities, tempeh fermentation showed release, transformation, and stimulated production of fiber-bound phenolics, glycosides and aglycones, and minor phenolics, respectively. Increases in the levels of free and bound phenolics suggest the conversion of bound phenolics to loosely-bound phenolics and free phenolics. This study concludes that tempeh fermentation can enhance the health-promoting potential of soybeans by modulating phenolic composition through release, transformation, and stimulated production