Investigation of lead and cadmium binding properties of lactic acid bacteria and yoghurt in in vitro conditions

The main purpose of this study is to investigate the heavy metal (Pb and Cd) binding and binding stability properties of lactic acid bacteria (LAB), to examine the heavy metal biosorption potential of yoghurts containing different LAB combinations and to determine biosorption effects in iv vitro model digestion system. Experiments are conducted under 3 main groups. In the first part, biosorption performances of 7 different commercial cultures of LAB were tested against factors such as temperature, incubation time, biomass and heavy metal concentration and pH. Thus, biosorption capacity of LAB strains under different conditions was determined. The data obtained from experiments were fitted into the Langmuir adsorption isotherm. Maximum binding capacities are calculated with this method and allowed us to compare biosorption capacities of different LAB cultures. It is observed that the most indicative parameter in the heavy metal biosorption of LABs is the pH. As an overall trend, as the pH values decreases, the biosorption capacity decreases as well; and is very limited at pH 3 and more acidic pH values. Although the temperature was seen to affect biosorption, this effect was limited in the range of 4 - 37 ° C. Experiments with different incubation times showed that the biosorption process takes place rapidly on the surface, largely in the first 5-30 minutes. But over a longer time, different mechanisms other than surface bonding may have took place. In the experiment of binding priority in which lead and cadmium were in the same environment, lead had been bound more. It has been found that probiotic LAB strains generally have a higher binding capacity (qmax) when examining biosorption capacities in conditions close to ideal. qmax value of the probiotic strain Lactobacillus acidophilus NCFM was found 75.1 mg/g (viable) and 68.2 mg/g (non-viable) for Pb; 16.4 mg/g (viable) and 28.1 mg/g (non-viable) for Cd. In the second part, biosorption performances of some strains (individually) and strain combinations that were found to perform well in the first experiments were examined in the yogurt matrice. It is determined that components other than the microorganisms found in yoghurt had an enhancing effect of biosorption capacity, and yoghurt prepared with higher binding strains performed better at binding heavy metals. In the third part, in vitro model digestive system was used to test the binding performance of strains which were found to have higher biosorption capacity in the previous experiments and certain matrices in conditions close to human digestive system (pH, duration, temperature, digestive fluids). It is determined that yoghurts containing LAB and probiotic strains have a significant potential to bind heavy metals via biosorption and reduce the absorption of heavy metals in the body.