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Functional foods provide health benefits beyond basic nutrition. A relevant health aspect regards the equilibrium between nutrients and beneficial gut-flora, especially Bidifobacterium spp. and Lactobacillus spp. Flavonoids are biologically active polyphenols with high antioxidant properties and demonstrated role in prevention of not-heritable diseases (cardiovascular diseases and cancer). Flavonoids are present in legumes mainly as O-glycosides: generally intestinal enzymes cannot hydrolyze the bond between the sugar moiety and the bioactive compound thus avoiding its uptake and subsequent health benefits. However, for some human intestinal Bifidobacterium species beta-glycosidase activity on flavonoids has been described (Marotti et al., 2007). The aim of the present research is to extend the monitoring of beta-glycosidase activity to lactic acid bacteria (LAB) commonly used in the food sector. The first step was to optimize the beta-glucosidase assay in MRS substrates in order to tune the experimental conditions in a medium suitable for LAB growth. For the experimental conditions setting up, two Bifidobacterium species were chosen on the basis of the results obtained in a previous work (Marotti et al., 2007): one strain of B. pseudocatenutalum for its high beta-glucosidase activity and one strain of B. longum lacking detectable activity. The beta-glycosidase activity was assayed by adding p-NPG (p-nitrophenyl- beta-D-glucopyranoside) in the growth medium and evaluating the pNP (p-nitrophenol) concentration after 14-24 hrs of incubation. The beta-glycosidase activity in B. pseudocatenulatum was independent from the growing medium (TPY or MRS) and from cell density; but it was influenced by substrate concentration. The optimized protocol was applied to 15 strains of LAB, including the following species: L. fermentum, L. buchneri, L. fructivorans, L. helveticus , L. acidophilus, L. plantarum, L. kefiri, L. jugurti, L. lactis, L. bulgaricus. The maximal beta-glycosidase activity was observed for L. buchneri, L. acidophilus and L. plantarum. These strains were previously isolated from tomato sauce and milk derived foods: they are therefore good candidates for developing functional food. Further studies are in progress with the aim to confirm the beta-glycosidase activity of these strains on typical legume flavonoids. |
