6832

6374

كارشناسي ارشد

علوم و صنايع غذايي

اصفهان: دانشگاه صنعتي اصفهان، دانشكده كشاورزي

1390

ده،99ص.: مصور،جدول،نمودار

ص.ع.به فارسي و انگليسي

صبيحه سليمانيان زاد، محمود شيخ زين الدين

محمد هادي اسكندري

19/4/91

علي نصيرپور، مسعود علي خاني

مهندسي كشاورزي

ID6374

به فارسي و انگليسي: قابل رويت در نسخه ديجيتالي

Screening of Lactobacilli Isolated from Traditionally Isfahan Zone Yoghurts for Bacteriocin Formation and Characterization of Produced BacteriocinExtended Abstract Nowadays consumers are increasingly demanding food that is free from pathogens withminimal processing and fewer chemical preservatives but with an unimpaired sensorial qualityand maximal shelf life Various suggestions are presented to achieving this aim and most ofthem are implying to biopreservation Biopreservation has gained increasing attention as meansof naturally controlling the shelf life and safety of foods with organisms especiallymicroorganisms or their products In the food industry Lactic acid bacteria LAB are widelyused as starter cultures LABs have some advantages that nominate them as a good choice forusing in biopreservation They have an important role in the inhibition of food borne pathogenicand spoilage microorganisms with antimicrobial metabolites They produce differentantimicrobial components in their defense system including lactic acid and other organic acids hydrogen peroxide di acetyl CO2 and bacteriocins Bacteriocins are ribosomally synthesizedpeptides or proteins usually antagonistic to closely related bacteria to producer Sincebacteriocins produced by LAB are considered to be Generally Recognized as Safemicroorganisms they are receiving much attention At the first part of our study we compared 3methods used for measuring bacteriocinegic activity of LABs including Spot on the lawn Agarwell diffusion assay AWDA and Photometric assay PA We showed Spot on the lawn methodwas introduced as more reproducible rapid and easy to score than Agar well diffusion andPhotometric assay Also the Photometric assay is more accurate than other 2 methods At thesecond part of our study 42 strains of lactobacillus delberueckii subsp bulgaricus that had beenisolated from conventional yoghurt were screened in terms of bacteriocinegic activity by Spot onthe lawn method and K41 strain showed the most inhibition activity against indicators Listeriamonocytogenes and Escherichia coli O157 H7 As most of the Bacteriocin like substancessecreted by LAB s are secondary metabolites the antimicrobial activity of the componentreleased by K41 was initially detected in the late exponential phase of growth and the maximumlevels of antimicrobial activity were found at the stationary phase This antibacterial peptide wasextremely heat stable 15 min at 121 C and was active over a wide pH range pH 2 10 It wasfound to be sensitive to proteolytic enzymes trypsin pepsin and proteinase K but resistant toamylase and lipase also the mode of its action was identified as bactericidal The inhibitoryspectrum of this peptide was tested against 10 food borne pathogenic and spoilagemicroorganisms including 5 G and 5 G bacteria and it exhibited a narrow range of inhibitoryactivity against G bacteria with extremely anti listerial activity on the other hand it was almostineffective against G bacteria In addition this study showed that non ionic detergents Tween 20 Tween 80 and Triton X100 had no effect on antimicrobial activity of produced peptide Toour knowledge this Bacteriocin Like Inhibitory Substance BLIS is related to class IIabacteriocins These characters suggest that BLIS of Lactobacillus bulgaricus subsp K41 is anovel Class II Bacteriocin with a narrow inhibitory spectrum and might be applicable in the foodindustries Keywords Biopreservative Bacteriocin Lactobacillus bulgaricus Screening Characterization

صبيحه سليمانيان زاد، محمود شيخ زين الدين

محمد هادي اسكندري

علي نصيرپور، مسعود علي خاني