[Potential ability of probiotics isolated from Iranian local yogurts to produce lactacins]

Lactic acid bacteria are microorganisms with ability to produce a wide range of chemical compounds that affect the shelf-life of foods. The objective of this study was to determine the potential ability of probiotics isolated from Iranian local yogurts to produce lactacins and assess their antimicrobial activity. Samples were prepared from 20 kinds of local yogurts [Arak, Sarein, Shahandasht, and Damavand] to isolate and purify lactic acid bacteria in an MRS agar medium and compare them with 3 isolated probiotics strains, i.e., L. casei [PTCC 1608], L. reuteri [PTCC 1655] and L. rhamnosus [PTCC 1637]. The inhibition of growth zone was tested, by the well diffusion agar method, on 5 gram-positive and gram-negative bacterial strains. The maximum amount of antimicrobial substance produced was determined by comparing the growth curves, and extraction purification of the lactacins was done by dialysis. In each stage the amount of protein extracted was determined by the Lowry method, and the recovery percent, total protein, unit activity, specific activity, purification fold, and bacteriocin field were calculated. The molecular weight of the extracted protein was determined by the SDS-PAGE method. A total of 21 lactic acid bacterial strains were isolated. The maximum antimicrobial components were found to be produced by Ln11 and Ld17 during the logarithmic phase of growth curve. The results of SDS-PAGE showed lactacins with molecular weights ranging from 48 to 57 KD. Considering the antimicrobial properties of the bacterial strains isolated from the local yogurts, they can be used as local probiotic strains in production of fermented foods in preference to the 3 standard strains