Diversity of biopolymers produced by thermophilic lactic acid bacteria: effect on the rheology of feremnted milks

CECILIA RODRÍGUEZ; JUDITH PIERMARIA; FERNANDA HAMET; LUC DE VUYST; FERNANDA MOZZI; GRACIELA FONT DE VALDEZ; ANALÍA ABRAHAM

Egmond aan Zee, Holanda

Simposio; 9th Symposium on lactic acid bacteria. Health, Evolution and Systems Biology; 2008

Federation of European Microbiology Societies and the Netherlands Society for Microbiology

Diversity of biopolymers produced by thermophilic lactic acid bacteria: effect on the rheology of fermented milks Cecilia Rodríguez1, Judith Piermaria2, Fernanda Hamet2, Luc De Vuyst3, Fernanda Mozzi1, Graciela Font de Valdez1 and Analía Abraham2 1Centro de Referencia para Lactobacilos (CERELA-CONICET), Chacabuco 145, 4000-Tucumán, Argentina. 2Centro de Investigación y Desarrollo en Criotecnología de Alimentos (CIDCA), 47 y 116, 1900-La Plata, Argentina. 3Research Group of Industrial Microbiology and Food Biotechnology (IMDO), Department of Applied Biological Sciences and Engineering, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium Exopolysaccharide (EPS) production by lactic acid bacteria (LAB) in milk improves the viscosity and texture of fermented milks. The textural characteristics of the fermented milks are strongly influenced by the EPS structural properties [molecular mass (MM) and chain stiffness] and the sugar polymer-producing strains [type of EPS: capsular (CPS) or slime EPS; ropiness, R]. The aim of this work was to evaluate the effect of EPS-producing LAB strains with the ability to synthesize different EPS on the rheological properties of fermented milks. Selected Streptococcus thermophilus (2) and Lactobacillus delbrueckii subsp. bulgaricus (5) strains were grown in sterilized low-fat milk at 37ºC for 16 h. All fermented milks (pH = 4.3-4.5) exhibited a pseudoplastic thixotropic behaviour and gel-type textures with different consistencies. No clear correlation between the apparent viscosity (happ) and the EPS concentration of the fermented milks was found. S. thermophilus CRL638 (low EPS producer, CPS-, high MM-EPS) showed the highest happ value and a weak gel-type texture. L. delbrueckii subsp. bulgaricus CRL553 and CRL142, both CPS-, R-, and producing a low-MM polygalactan, displayed significant happ values and weak gel-type textures but firmer than that of strain CRL638. Interestingly, L. delbrueckii subsp. bulgaricus CRL861, which synthesized low amounts of a low-MM EPS, showed a strong gel-type texture with high viscosity. Ropy strains resulted in high-viscosity fermented milks. To conclude, adequate in situ use of sugar polymer-producing LAB in the fermented dairy industry is strongly influenced by their EPS structure-function relationships.