مقالات رزومه دکتر ماندانا محمودی

In this study, milk fermentation capability by 6 isolates of lactic acid bacteria, proteolytic activity of lactic acid bacteria in milkby ortho-phthaldialdehyde (OPA)reagentand antifungal property of lactic acid bacteria in MRS broth and skim milk against Aspergillus flavus and Candida albicanswere studied. L. brevis KMJC1, L. acidipiscis KMJC2, L. curvatus KMJC3 and L. plantarum KMJC4 isolated from Jug cheese, L. helveticus KMCH1 isolated from camel doogh (Chal) and Lac. lactis KMCM3 isolated from camel milk were used. The results showed thatamong the isolates,L. plantarum KMJC4after 48 h, Lac. lactis KMCM3 after 16 hand L. helveticus KMCH1 after 60 hhad milk fermentation capability. The measurement of proteolysis rate performed infermented milk by mentioned isolates using OPA reagent indicated that the proteolytic activity of L. helveticus KMCH1, Lac. lactis KMCM3 and L. plantarum KMJC4 were 0.34, 0.26 and 0.22 mg/ml, respectively. In study of the antifungal effect of supernatant resulting from the activity of lactic isolates, it was found that supernatant obtained from culture in MRS broth had a more inhibitory effect (MIC= 25 and 50 mg/ml) than the supernatant obtained from the culture in the skim milk, as the MIC was not observed for the supernatant obtained from fermented milk. In the end, it can be concluded that Lac. lactis KMCM3 was able to ferment lactose in milk in comparisonwith other isolates in shorter time (16 h). The highest proteolytic activity of the isolates in milk was related to the isolate of L. helveticus KMCH1 (0.34 mg/ml). L. plantarum KMJC4 isolated from Jug cheese was as the best isolate for the preparation of supernatant resulting from MRS broth with the antifungal property.

 Today, despite improved food safety, nearly a quarter of the population is at risk for foodborne diseases. Therefore, the use of lactic acid bacteria and their metabolites due to their potential health benefits, safety and production of natural antimicrobial compounds is an appropriate solution to reduce microbial spoilage of food.

   In this research, lactic isolates were first identified by PCR method and Micro-dilution method was used to evaluate the antimicrobial activity of the Cell Free spent Medium (CFSM).

   The sequencing of PCR products showed that the species identified were Lactobacillus and Enterococcus species. The results of the evaluation of the antibacterial properties of the CFSM on the growth of Gram-positive bacteria showed that all isolates were able to prevent the growth of these pathogens and their inhibitory percentages varied from 86.81 to 38.81 percent. The results of inhibitory effects of lactic isolates on the growth of two gram-negative bacteria of Escherichia coli and Salmonella enterica also showed that the inhibitory levels of the isolates were varied from 2.43 to 36.43 percent and 14.1 to 31.97 percent, respectively. Comparison of the inhibitory effect of lactic isolates on pathogenic bacteria showed that the inhibitory effect of all lactic isolates on gram positive bacteria was significantly (P <0.05) more than their effect on gram negative bacteria.

  The results of this study showed that native dairy lactic acid isolates and their metabolites can be used as biological preservatives or in combination with synthetic preservatives in the food and drug industry.