Genotypic and Phenotypic Characterization of Exopolysaccharide-producing Lactobacillus strains isolated from kefir grains

GANGOITI, M.V. ; HAMET, M. F.; MEDRANO, M.; PUERTAS, A. I.; PIERMARIA, J.; DUEÑAS, M. T. ; ABRAHAM, A. G.

San Miguel de Tucumán

Simposio; IV International Symposium on Lactic Acid Bacteria Food, Health and Applications; 2013

Some!lacSc!acid!bacteria!(LAB)!isolated!from!kefir!grains,!exert!the!ability!to!develop!ropy!colonies! when! growing! in! MRS8Agar,! that! could! be! associated! to! exopolysaccharide! (EPS)! producing! bacteria.!EPS!producing!LAB!have! the!ability! to!synthesize!in&situ&these!biopolymers,!which!could! act! as! natural! thickening! agents,! improving! texture! on! fermented! products.! This! ability,! and! the! GRAS!status! that!LAB!possesses,!confers! these!microorganisms!an!addiSonal!value! to!be!used!on! dairy! industry.! The! aim! of! the! present! study! was! to! conduct! a! genotypic! and! phenotypic! characterizaSon! of! the! EPS! producSon! of! 3! Lactobacillus& paracasei! strains! (CIDCA! 8339,! CIDCA! 83123,! CIDCA! 83124)! and! 2! L.& kefiranofaciens! strains! (CIDCA! 83118,! CIDCA! 83119)! isolated! from! kefir! grains.! For! genotypic! characterizaSon,! the! presence! of! the! priming! enzyme! glycosyl! transferase! (pGT)! 8essenSal! for! heteropolysaccharides! synthesis8! was! determined! by! PCR.! The! obtained!products!were!amplified!and!sequenced,!finding!that!the!pGT!gen!was!present!in!all!the! studied!strains.!For!phenotypic!characterizaSon,!all!the!microorganisms!were!grown!in!milk!under! their! respecSve!opSmal!culture!condiSons,!and!EPS!producSon!was!characterized.!EPS!produced! by! these! strains!was!between!140!and!301,9!mg/l.!Molecular!weight!of!EPSs!was!determined!by! high! pressure! liquid! chromatography! (HPLC)! using! a!molecular! exclusion! column! associated! to! a! refracSon!index!detector.!Different!fracSons!were!found,!with!molecular!weights!between!1048106 Da!for!EPSs!produced!by!L.¶casei!and!1028105!Da!for!those!produced!by!L. kefiranofaciens.!To! conduct! all! the! determinaSons,! two! EPS! producing! strains! were! used! as! posiSve! controls:! L.& delbrueckii&subsp!bulgaricus&CIDCA!332!and!L.&kefiranofaciens&subsp!kefiranofaciens&JCM!6985.!The! evaluaSon! of! the! flow! curves! of! the! fermented! products! of! all! the! studied! strains! showed! a! pseudoplasSc!fluid!behavior,!and!presented!apparent!viscosity!values!and!hysteresis!areas!higher! to! acid! milk! gels! obtained! by! chemical! acidificaSon! of! milk! with! δ8gluconolactona.! It! can! be! concluded! that! Lactobacillus! studied! possess! the! gen! encoding! enzyme! responsible! for! heteropolysaccharide!synthesis.!The!phenotypic!expression!of!this!gen!results!in!the!producSon!of! EPSs!that!modify!rheological!behavior!of!fermented!milks.!Taking!into!account!the!present!results! these! strains! and! the! EPSs! they! produce! are! interesSng! candidates! for! their! applicaSon! in! food! industry.