Determination the minimum inhibitory concentration of zinc sulfate on growth and maximum biosorption in probiotics, Lactobacillus acidophilus and Candida utilis

Probiotics are non-pathogenic microorganisms that have beneficial effects on living organisms. Also, zinc as a micronutrient has useful properties and is essential for the body of living organisms. Probiotics and zinc can have a positive role in the health of living organisms with their synergistic effects. Small amounts of micronutrients are needed for the growth and development of living organisms, but large amounts of them can be toxic. Micronutrients are found in nature in two forms, inorganic and organic, which the organic form is less toxic. Bacteria and fungi are among the microorganisms that can convert minerals into organic forms and reduce their toxicity. Therefore, in this study, two probiotics, Lactobacillus acidophilus and Candida utilis, were selected and their ability to absorb and accumulate mineral zinc as well as the growth rate of the microorganisms were investigated. For this purpose, 9 different concentrations of zinc sulfate including 0.05, 0.2, 15, 10, 5, 25, 50, 75, and 100 mmol/l were used. Based on the results, the growth inhibition of L. acidophilus and C. utilis probiotics was obtained at 100 and above 50 mmol/L, respectively. The highest and lowest amounts of zinc absorption in L. acidophilus were 2364 and 498.8 ppm, respectively, and in C. utilis were 41830 and 13174 ppm, respectively. Based on the findings of the present study, it can be concluded that each of these two probiotics has specific capacities in zinc absorption and tolerance based on their cellular structure. The reason for that can be in the mechanism and mode of action and intracellular mechanisms and bacteria have a lower absorption rate than yeast due to the presence of a cell wall. Therefore, the selected bacteria and yeast can absorb zinc and they have various applications in the food and drug industry as a zinc-enriched probiotics.