Year: 2006
Type: dissertation
Abstract: Kefir is a traditional fermented milk that is carbonated, has a sharp acidic taste, yeasty flavour and contains a low percentage alcohol (less than 2% (v/v)).The beverage is manufactured by fermenting milk with Kefir grains, comprised of microorganisms, polysaccharides and milk proteins.The microbial population of Kefir grains primarily include lactic acid bacteria (LAB), namely lactococci and lactobacilli, yeasts, Acetobacter and filamentous fungi.Kefir exhibits antimicrobial activity in vitro against some fungi, and Grampositive and Gram-negative bacteria.Although the exact cause of this inhibition in Kefir is not known, the ability of LAB to inhibit the growth of closely related bacteria is well known.This inhibition of pathogenic and spoilage microbes may be due to the production of organic acids, hydrogen peroxide, acetaldehyde, diacetyl, carbon dioxide or bacteriocins.Acid is not the only contributor to the antimicrobial activity of Kefir and Kefir grains, and bacteriocins may play a role in the inhibitory activity.The bacteriocin producer Lactobacillus plantarum ST8KF, isolated from Kefir and Kefir grains, produces a bacteriocin 3.5 kDa in size.The mode of activity of bacteriocin ST8KF (bacST8KF) is thought to be bacteriostatic in exponential cultures of Enterococcus faecalis E88, Lactobacillus casei LHS, Lactobacillus curvatus DF38, Lactobacillus sakei DSM 20017, Lactobacillus salivarius 241 and Listeria innocua F and LMG 13568.The peptide is sensitive to proteolytic enzymes and does not adsorb to the surface of the producer cell.The bacteriocin is stable between pH 2.0 and 10.0, and for 20 min at 121°C.Maximum bacteriocin activity was observed in modified MRS medium supplemented with glucose or saccharose, meat extract, KH 2 PO 4 , glycerol, thiamine or cyanocobalamin, or in modified MRS medium without tri-ammonium citrate.Maximum levels of adsorption of bacST8KF (80%) to Lb. casei LHS and Lb.sakei DSM 20017 were recorded.Adsorption (80%) of the bacteriocin to Lactobacillus paraplantarum ATCC 700211 T and Streptococcus caprinus ATCC 700066, which are not sensitive to the bacteriocin was also recorded.Optimal adsorption to E. faecalis E88 was recorded at 25°C at pH 2.0, and to L. innocua LMG 13568 at 4°C, 10°C and 25°C at pH 6.0.Potassium ions, MgCl 2 , Tris, NH 4citrate, Na-acetate, Na 2 CO 3 , EDTA and SDS led to decreased adsorption to both UITTREKSEL Kefir is 'n tradisioneel-gefermenteerde en gekarboneerde melk drankie.Dit het 'n skerp suur smaak, gis aroma en het 'n lae alkohol inhoud (minder as 2% v/v).Die drankie word vervaardig deur melk met Kefir korrels te fermenteer.Die korrels bestaan uit mikro-organismes, polisakkariede en melk proteïene.Die mikrobiese populasie van Kefirkorrels sluit hoofsaaklik melksuur bakterieë (LAB), naamlik lactococci en lactobacilli, giste, Acetobacter en miseliêre fungi in.Kefir toon antimikrobiese aktiwiteit, in vitro, teen sommige fungi, en Grampositiewe en -negatiewe bakterieë.Alhoewel die presiese oorsaak vir hierdie inhibisie onbekend is, is die vermoë van LAB om groei in naverwante baketerieë te inhibeer bekend.Die produksie van organiese sure, waterstofperoksied, asetaldehied, diasetiel, koolstofdioksied en/of bakteriosiene kan lei tot die inhibisie van patogene en bederf mikrobes.Dit is gewys dat suur nie die enigste bydrae tot die antimikrobale aktiwiteit van Kefir en Kefir korrels lewer nie.Bakteriësiene mag ook 'n rol in die inhibisie speel.Die bakteriosien produseerder, Lactobacillus plantarum ST8KF, is geïsoleer uit Kefir en Kefirkorrels, en produseer 'n bakteriosien (bacST8KF) van 3.5 kDa.Dit word gedink dat hierdie bakteriosien bakteriostaties is, en dus effektief teen eksponënsie kulture van Enterococcus faecalis E88, Lactobacillus casei LHS, Lactobacillus curvatus DF38, Lactobacillus sakei DSM20017, Lactobacillus salivarius 241 en Listeria innocua F en LMG 13568 is.BacST8KF is sensitief vir proteolitiese ensieme en absorbeer nie aan die oppervlakte van die produseeder sel nie.Die bakteriosien is stabiel tussen pH 2.0 en 10.0, en teen 121°C vir 20 min.Maksimum bakteriosien aktiwiteit is gevind in gemodifiseerd MRS-medium wat verryk is met glukose of sukrose, vleis-ekstrak, KH 2 PO 4 , gliserol, tiamien of sianokobalamien, of in gemodifiseerd MRS-medium sonder tri-ammonium sitraat.Maksimum vlakke van adsorpsie van bacST8KF (80%) aan Lb. casei LHS en Lb. sakei DSM 20017 is gevind.Absorpsie (80%) van die bakteriosien aan Lactobacillus paraplantarum ATCC 700211 T en Streptococcus caprinus ATCC 700066, wat nie sensitief teenoor die bakteriosien is nie, was ook gevind.'n pH van 2.0 en 20°C het gelei tot die beste adsorpsie aan E. faecalis E88, en 4°C, 10°C en 25°C by pH 6.0 was die beste vir absorpsie aan L. innocua LMG 13567.Kalium ione, MgCl 2 , Tris, NH 4 -sitraat, Na-asetaat, Na 2 CO 3 , EDTA en SDS het swakker absorpsie tot gevolg gehad, terwyl NaCl en -merkapto-ehanol 'n afname in absorpsie aan E. faecalis E88, maar nie tot L. innocua LMG 13568, getoon het.Metanol het swakker adsorpsie aan L. innocua LMG 13568 getoon, maar nie aan E. faecalis E88 nie.Triton X-100 en Triton X-114 het die adsopsie van bacST8KF met 40% verhoog, terwyl etanol en chloroform geen effek op bakteriosien adsorpsie getoon het nie.Die behandeling van L. innocua E88 en E. faecalis LMG 13568 met bacST8KF het 'n daling van twee log siklusse tot gevolg gehad, en die groei van Lb. plantarum ST8KF en L. innocua LMG 13568 in 'n gemengde kultuur het 'n toename in bacST8KF produksie tot gevolg gehad.Die venietiging
Author: Jillian E. Powell
Language: English
Subfield: Food Science
Domain: Life Sciences
SDG: Zero hunger
Open Access status: green
OpenAlex ID: W2155031247