Nature du caractère épaississant de certaines souches de Streptococcus thermophilus ; étude préliminaire

Abstract

RésuméTrois souches épaississantes de S. thermophilus et une non épaississante ont été comparées après culture, soit dans du lait à différentes températures, soit dans d'autres milieux: lait supplémenté ou dialysé, lactosérum et milieu Elliker à 44 oc.Les souches épaississantes se caractérisent par une augmentation de la viscosité qui ne se manifeste que dans le lait mais pas dans les autres milieux. Ces souches produisent plus de polysaccharides solubles que la souche non épaississante mais les quantités sont faibles (:% 40 mg/l) et pas en rapport avec les variations de viscosité observées. A 30 "C, les souches épaississantes produisent de 4 à 8 fois plus de glucides insolubles que la souche non épaississante mais, dans les autres cas, les différences sont beaucoup plus faibles. Quelles que soient les conditions de culture dans le lait, les profils électrophorétiques des caséines sont les mêmes pour les quatre souches.A partir de ces résultats il est difficile de conclure sur la nature possible du composé responsable des propriétés épaississantes de ces souches de S. thermophilus mais plusieurs hypothèses sont émises.Mots clés: S. thermophilus -Souches épaississantes -Viscosité -PolysaccharidesProtéolyse. Summary Nature of the viscous character of some Streptococcus thermophilus strains : a preliminary investigationThree ropy and one non ropy strains of S. thermophilus were compared after growth either in skim milk at various tempe ratures or in supplemented or dialyzed milk, whey and Elliker medium at 44 oc. Ropy strains exhibited increase in relative viscosity only in milk media but not in the other ones. They produced more soluble polysaccharides than the non ropy strain but the amounts were low (:% 40 mg/l) and not related to the viscosity. At 30 "C, ropy strains produced 4 to 8 times more insoluble glucides than the non ropy strain but in the other cases the differences were generally 286 G. GIRAFFA et l.L. BERGÈRE lower. Whatever the culture conditions in milk, electrophoretic pattern of caseins were quite similar for the four strains.From this results it is difficult to conclude on the nature of the viscous character of S. thermophilus but sorne hypothesis are postulated.

Heteropolysaccharides from lactic acid bacteria

“…However, contradictory results have been reported regarding the influence of physical and chemical factors on EPS production by LAB. Since no EPS production was initially observed in MRS or synthetic media, milk was the medium studied [18, 19, 21, 38, 43, 45, 60, 64, 87–90]. Also whey and whey‐based media have been studied [91].…”

Effects of starter culture and its exopolysaccharides on the gelation of glucono‐δ‐lactone‐acidified bovine and caprine milk

“…The polymers extracted from streptococci, however, were found to be produced at much lower yields e.g. 40–75 mg/L, 10,11 15–35 mg/mL 12 . They were excreted in the form of discrete capsules of material: either glycoproteins 10 or heteropolysaccharides of complex chemical composition (containing diacetyl, N‐acetylogalactosamine and lipoteichoic acid 13,14 or galactose, glucose and glucosamine 15 ).…”

Preparation of polysaccharide fromStreptococcus thermophilus using an enzymatic ultrafiltration reactor

“…These polysaccharide yields compare favorably with those obtained by Tsuchiya et al (1981) for MPS-80 polysaccharide isolated from whey powder solution inoculated with Streptococcus thermophilus.polysaccharide. We obtained about three times more polysaccharide thanCerning et al (1988) andGiraffa & Berg~re. (1987) with a different carbohydrate composition (glucose: i; galactose: 1 and minor others monosaccharides,CERNING et al 1988).…”

“…Streptococcus thermophilus and Lactobacillus bulgaricus used in Dairy starter cultures produced polysaccharides which have been studied by many authors (Schellhaass, 1983;Manca de nadra et al ,1985;Giraffa & Berg~re, 1987;Cerning et al ,1986Cerning et al , , 1988).…”