Factors Affecting Lactic Acid Bacteria Adsorption of Aflatoxin and the Effect of Adsorbed Toxin on Rats' Liver Tissues

Abstract

Aflatoxin adsorption property of lactic acid bacteria could be used as a detoxification method which is most appropriate for food and dairy products. Seven strains of lactic acid bacteria (Lactobacillus casei, Lactobacillus gasseri, Lactobacillus reuteri, Lactobacillus bulgaricus, Lactobacillus acidophilus, Streptococcus thermophilus, Bifidobacterium bifidium) plus two mixed commercial cultures FD-DVS YCX11 50U (Lactobacillus bulgaricus+ Streptococcus thermophilus) and FD-DVS ABT2 50U (Lactobacillus acidophilus+ Streptococcus thermophilus +Bifidobacterium bifidum) were tested for their AFB1 and AFM1 adsorption rate, Factors affecting such adsorption were studied. The bioavailability of the adsorbed toxin was determined by feeding rats with L. casei-AFB1, L. casei-AFM1 complexes, and both toxins and rats liver tissues were examined. Adsorption reaction was carried out in 1 ml of phosphate buffer saline containing 1µg of the toxin and about 1.7x10 11 CFU of bacteria at 37° C for 2 hrs and pH of 7.3. out of the tested strains,L. casei showed the highest toxin removal rate of 34.1% and 27.7% for AFB1 and AFM1, respectively. These rates were increased by reducing the toxin into 0.5µg /ml, lowering the reaction pH into acidic pH and using acid or heat killed cells. Moreover, the rate was increased by adapting L. casei to toxin adsorption by repeated exposure to toxin, the rate increased from 34.1% to 50% of AFB1. Toxin concentration higher than 0.5µg / ml reduced the adsorption and caused changes in cell morphology. Aflatoxin bound by bacteria showed no toxicity effect on rats. Liver tissues of rats fed on the toxin complex were normal structure as compared to tissues of rats fed on free toxins which showed macroviscular fatty change, hydropic degeneration and congested hepatic sinusoids. the toxin complex was not absorbed since it did not adhere to intestinal wall. Yoghurt and sweet cultured milk were processed from AFM1 contaminated milk using L. casei culture.