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

RODRÍGUEZ, C.; PIERMARÍA; J., HAMET, F., DE VUYST, L., MOZZI, F., FONT DE VALDEZ, G., ABRAHAM, A.G

Egmond aan Zee, Holanda

Congreso; 9th Symposium on Lactic Acid Bacteria. Health, Evolution and Systems Biology. Federation of European Microbiological Societies and The Netherlands Society for Microbiology.; 2008

Federation of European Microbiological Societies and the Netherlands Society for Microbiology.

The rheology of the fermented milks are strongly influenced by the exopolysaccharide (EPS) structural properties (molecular mass, MM, and chain stiffness) and the biopolymer-producing lactic acid bacteria (LAB) [type of EPS produced: capsular (CPS)- or slime; ropiness, R, etc.]. The aim of this work was to evaluate the effect of EPS-producing LAB strains with ability to synthesize different EPS, on the rheological properties of fermented milks. Streptococcus thermophilus (2 strains) and Lactobacillus delbrueckii subsp. bulgaricus (5) were grown in sterilized low-fat milk at 37ºC for 16 h. The rheological properties of fermented milks were determined in shear and dynamic modes using a Haake RheoStress 600 rheometer coupled with a parallel-plate sensor at 20ºC. Apparent viscosity (happ) was determined at 300seg-1. Small-deformation oscillatory measurements were performed at stress of 0,1Pa and storage modulus (G’) and loss modulus (G”) at a frequency of 1Hz. All fermented milks (pH= 4.3-4.5) exhibited pseudoplastic thixotropic behaviour and gel-type structures with different consistencies. No clear correlation between the happ and the EPS concentration was found. S. thermophilus CRL638 (low EPS-producer, CPS-, high MM-EPS) showed the highest happ values (126,75 mPa.s) and a weak gel-type structure (G’:27.93Pa and G”:8.21Pa). L. delbrueckii subsp. bulgaricus CRL553 and CRL142, both CPS-, R- and low-MM polygalactan producers, displayed important happ values (82,32 and 74,33 mPa.s, respectively) and weak gel-type structures. Interestingly, L. delbrueckii subsp. bulgaricus CRL861, which synthesized scarce amounts of a low-MM EPS, showed high viscosity (80,83 mPa.s) and high G’ (74.7Pa) and G” (21.8Pa) values. Fermented milks using ropy strains displayed high viscosity values. The adequate in situ use of polymer-producing LAB in the dairy industry is strongly influenced by their EPS structure-function relationships.