The role of Bifidobacterium lactis and the effect of the addition of inulin and lactulose on the viscosity of a functional fermented milk product have been investigated. The effect of chosen starter and prebiotics on the properties of the functional fermented milk was significant for the apparent viscosity. Generally the viscosity of analyzed products was lower than the viscosity of classical fermented milk products, such as yoghurt, kefir or others. The viscosity was strongly affected by the content of total solids of the analyzed products: with an increase in the total solids there was increase in the viscosity. Among analyzed fermented milk samples, sample with 5% of lactulose had the highest viscosity. In general, inulin did not seem to have an effect on the viscosity of the analyzed product samples compared with the control sample. Bifidobacterium lactis has a weak proteolytic activity; therefore the structure and consistency of functional fermented milk product were characterized as weak, too. It is known that inulin is not only dietary fibre or prebiotic, it has the functions of food additives, too. Inulin is added to food formulations to modify products' texture or viscosity and sweetness of products. Comparison of the obtained results shows that the viscosity of the functional fermented milk product with various concentrations of lactulose or inulin is different. This suggests that the role of inulin in a food matrix is bi-functional. Inulin does not increase the viscosity of a milk product but gives a richer texture to liquid products and spreads.

Fermentation of milk with probiotics and prebiotics has been shown to increase the concentration of B group vitamins in fermented milk products. The task of the study was to investigate the influence of prebiotics on the increasing of thiamin and riboflavin concentrations in milk during fermentation by Bifidobacterium lactis. Lactulose (Duphilac, Netherlands) and inulin (Raftiline, Belgium) were added (1, 2, 3, 4 and 5%) into 100 g of milk. The milk samples were inoculated with Bifidobacterium lactis (BB-12, Chr. Hansen, Denmark) and incubated at 38 deg C for 16 hours. The amount of thiamine and riboflavin was determined by fluorometric method. Laboratory studies have shown that the increasing of thiamin and riboflavin concentrations in milk depends on the concentration of lactulose and inulin. Data on the final thiamin and riboflavin concentrations in fermented milk indicates that increasing the lactulose concentration from 1% to 3% enhanced the production of thiamin and riboflavin. The similar data was obtained with inulin. Increasing of inulin concentration from 1% to 4% enhanced the production of vitamins thiamin and riboflavin. The present results furthermore indicate that finding optimal combination of prebiotics and probiotic pairs where the prebiotic would benefit the specific probiotic strain, e.g. during production and formulation into foods, is one of the research priority for functional foods.

In this work the combinations of commercial lactic acid bacteria starters and acetic acid bacteria strain were used for production of fructans in substrate, both with and without sucrose additive, and studied their potential in maintaining technological properties of yoghurt and fermented milk. The objective of this study was to assess the effect of fructans producing starter cultures on milk coagulation technique, the amount of secreted fructans and viscosity of fermented milk samples. An amount of fructans synthesized by starter cultures and Gluconobacter sp. B35, pH and viscosity of samples were measured using appropriate standards and analytical methods. Results showed that the addition of acetic acid bacteria did not influence the pH dynamics of fermented milk samples. Increasing sucrose concentration in samples significantly influences fructans production potential. The application of such technology in fermented dairy product production would have potential from microbiological exopolysaccharides increasing position with the aim to promote functionality of dairy foods and to substitute commercial stabilisers etc. The addition of acetic acid bacteria in milk showed negative impact on viscosity of the evaluated samples. The viscosity was liquid in all analyzed samples with acetic acid bacteria, the addition of sucrose helped to make the consistency of yoghurt and fermented milk more liquid. We concluded that the structure of synthesized fructans could not help to improve the textural properties of fermented dairy products. From this point of view, the studied acetic acid bacteria strain should have the potential as prebiotic.