DOES THE LACTIC ACID BACTERIA FERMENTATION PLAYS A SIGNIFICANT ROLE ON TOFU PHENOLIC COMPOUNDS COMPOSITION?

Background and objectives: The high nutritional value and low cost of soybean products make them a suitable solution for malnutrition problems for poor people living on grain centred diets. Tofu, a fundamental part of Asian food culture, is a traditional oriental soybean food and it may be the most popular food made of soy worldwide. Thousands of studies (in vivo and in vitro, with animals and human subjects) have shown that soybeans and soy components have many health-promoting effects; some of them were attributed to the isoflavones. In particular, various forms of isoflavones have been shown to possess different antioxidant activities. The aim of the study was to investigate the effect of lactic acid bacteria (LAB) fermentation on the free and bound phenolic fraction of tofu. Methods: The fermentation process was established using specific strains of lactic acid bacteria. Free and bound phenolic compounds from soybean, traditional tofu and tofu obtained by soymilk fermentation were studied by HPLC-DAD-ESI-MS. Results: Important effects of fermentation were seen on isoflavone profile: in fact, isoflavones content of fermented tofu showed significant differences compared to soybean and to traditional tofu. In particular, fifteen isoflavones were identified as aglycones and glycosides: the aglycone forms were significantly higher in fermented tofu compared to the traditional one. The ratio of aglycones/glycosylated isoflavones was 0.34 and 2.55 for the traditional and fermented tofu, respectively. Soy and traditional tofu presented the same content of bound phenolic compounds (mainly phenolic acids), instead fermented tofu showed a bound phenolic content 34 % higher than traditional tofu. Conclusions: These results suggest that fermentation by LAB plays an essential role in the increase of the content of aglycone isoflavones and bound phenolic compounds with important biologically implications on human health.